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    <title>erl_nif</title>
    <prepared>Sverker Eriksson</prepared>
    <responsible>Sverker Eriksson</responsible>
    <docno>1</docno>
    <approved></approved>
    <checked></checked>
    <date>2009-11-17</date>
    <rev>PA1</rev>
    <file>erl_nif.xml</file>
  </header>
  <lib>erl_nif</lib>
  <libsummary>API functions for an Erlang NIF library</libsummary>
  <description>
    <p>A NIF library contains native implementation of some functions
    of an Erlang module. The native implemented functions (NIFs) are
    called like any other functions without any difference to the
    caller. Each NIF must also have an implementation in Erlang that
    will be invoked if the function is called before the NIF library
    has been successfully loaded. A typical such stub implementation
    is to throw an exception. But it can also be used as a fallback
    implementation if the NIF library is not implemented for some
    architecture.</p>     
    <marker id="WARNING"/>
      <warning><p><em>Use this functionality with extreme care!</em></p>
      <p>A native function is executed as a direct extension of the
      native code of the VM. Execution is not made in a safe environment.
      The VM can <em>not</em> provide the same services as provided when
      executing Erlang code, such as preemptive scheduling or memory
      protection. If the native function doesn't behave well, the whole
      VM will misbehave.</p>
      <list>
	<item><p>A native function that crash will crash the whole VM.</p></item>
	<item><p>An erroneously implemented native function might cause
	a VM internal state inconsistency which may cause a crash of the VM,
	or miscellaneous misbehaviors of the VM at any point after the call
	to the native function.</p></item>
	<item><p>A native function that do <seealso marker="#lengthy_work">lengthy
	work</seealso> before returning will degrade responsiveness of the VM,
	and may cause miscellaneous strange behaviors. Such strange behaviors
	include, but are not limited to, extreme memory usage, and bad load
	balancing between schedulers. Strange behaviors that might occur due
	to lengthy work may also vary between OTP releases.</p></item>
      </list>
      </warning>

    <p>A minimal example of a NIF library can look like this:</p>
      <p/>
      <code type="none">
/* niftest.c */
#include "erl_nif.h"

static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
    return enif_make_string(env, "Hello world!", ERL_NIF_LATIN1);
}

static ErlNifFunc nif_funcs[] =
{
    {"hello", 0, hello}
};

ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)
</code>

    <p>and the Erlang module would have to look something like
    this:</p>
      <p/>
      <code type="none">
-module(niftest).

-export([init/0, hello/0]).

init() ->
      erlang:load_nif("./niftest", 0).

hello() ->
      "NIF library not loaded".
</code>
    <p>and compile and test something like this (on Linux):</p>
      <p/>
      <code type="none">
$> gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/
$> erl

1> c(niftest).
{ok,niftest}
2> niftest:hello().
"NIF library not loaded"
3> niftest:init().
ok
4> niftest:hello().
"Hello world!"
</code>

     <p>A better solution for a real module is to take advantage of
     the new directive <seealso
     marker="doc/reference_manual:code_loading#on_load">on_load</seealso> to automatically
     load the NIF library when the module is loaded.</p>
     <note><p>A NIF does not have to be exported, it can be local to the module.
     Note however that unused local stub functions will be optimized
     away by the compiler causing loading of the NIF library to fail.</p>
    </note>
     <p>A loaded NIF library is tied to the Erlang module code version
     that loaded it. If the module is upgraded with a new version, the
     new Erlang code will have to load its own NIF library (or maybe choose not
     to). The new code version can however choose to load the exact
     same NIF library as the old code if it wants to. Sharing the same
     dynamic library will mean that static data defined by the library
     will be shared as well. To avoid unintentionally shared static
     data, each Erlang module code can keep its own private data. This
     private data can be set when the NIF library is loaded and
     then retrieved by calling <seealso marker="#enif_priv_data">enif_priv_data</seealso>.</p>
    <p>There is no way to explicitly unload a NIF library. A library will be
     automatically unloaded when the module code that it belongs to is purged
     by the code server.</p>

  </description>
  <section>
  <title>FUNCTIONALITY</title>
  <p>All functions that a NIF library needs to do with Erlang are
      performed through the NIF API functions. There are functions
      for the following functionality:</p>
    <taglist>
      <tag>Read and write Erlang terms</tag>
      <item><p>Any Erlang terms can be passed to a NIF as function arguments and
      be returned as function return values. The terms are of C-type
      <seealso marker="#ERL_NIF_TERM">ERL_NIF_TERM</seealso>
      and can only be read or written using API functions. Most functions to read
      the content of a term are prefixed <c>enif_get_</c> and usually return
      true (or false) if the term was of the expected type (or not).    
      The functions to write terms are all prefixed <c>enif_make_</c> and usually
      return the created <c>ERL_NIF_TERM</c>. There are also some functions
      to query terms, like <c>enif_is_atom</c>, <c>enif_is_identical</c> and
      <c>enif_compare</c>.</p>
      <p>All terms of type <c>ERL_NIF_TERM</c> belong to an environment of type
      <seealso marker="#ErlNifEnv">ErlNifEnv</seealso>. The lifetime of a term is
      controlled by the lifetime of its environment object. All API functions that read
      or write terms has the environment, that the term belongs to, as the first
      function argument.</p></item>
      <tag>Binaries</tag>
      <item><p>Terms of type binary are accessed with the help of the struct type
      <seealso marker="#ErlNifBinary">ErlNifBinary</seealso>    
      that contains a pointer (<c>data</c>) to the raw binary data and the length
      (<c>size</c>) of the data in bytes. Both <c>data</c> and <c>size</c> are
      read-only and should only be written using calls to API functions.
      Instances of <c>ErlNifBinary</c> are however always allocated by the user
      (usually as local variables).</p>
      <p>The raw data pointed to by <c>data</c> is only mutable after a call to
      <seealso marker="#enif_alloc_binary">enif_alloc_binary</seealso> or
      <seealso marker="#enif_realloc_binary">enif_realloc_binary</seealso>.
      All other functions that operates on a binary will leave the data as read-only.
      A mutable binary must in the end either be freed with
      <seealso marker="#enif_release_binary">enif_release_binary</seealso>
      or made read-only by transferring it to an Erlang term with
      <seealso marker="#enif_make_binary">enif_make_binary</seealso>.
      But it does not have to happen in the same NIF call. Read-only binaries
      do not have to be released.</p>
      <p><seealso marker="#enif_make_new_binary">enif_make_new_binary</seealso>
      can be used as a shortcut to allocate and return a binary in the same NIF call.</p>
      <p>Binaries are sequences of whole bytes. Bitstrings with an arbitrary
      bit length have no support yet.</p>
       </item>
      <tag>Resource objects</tag>
      <item><p>The use of resource objects is a safe way to return pointers to
      native data structures from a NIF. A resource object is
      just a block of memory allocated with
      <seealso marker="#enif_alloc_resource">enif_alloc_resource</seealso>.
      A handle ("safe pointer") to this memory block can then be returned to Erlang by the use of
      <seealso marker="#enif_make_resource">enif_make_resource</seealso>.
      The term returned by <c>enif_make_resource</c>
      is totally opaque in nature. It can be stored and passed between processes
      on the same node, but the only real end usage is to pass it back as an argument to a NIF.
      The NIF can then call <seealso marker="#enif_get_resource">enif_get_resource</seealso>
      and get back a pointer to the memory block that is guaranteed to still be
      valid. A resource object will not be deallocated until the last handle term
      has been garbage collected by the VM and the resource has been
      released with <seealso marker="#enif_release_resource">enif_release_resource</seealso>
      (not necessarily in that order).</p>      
      <p>All resource objects are created as instances of some <em>resource type</em>.
      This makes resources from different modules to be distinguishable. 
      A resource type is created by calling
      <seealso marker="#enif_open_resource_type">enif_open_resource_type</seealso>
      when a library is loaded. Objects of that resource type can then later be allocated
      and <c>enif_get_resource</c> verifies that the resource is of the expected type.
      A resource type can have a user supplied destructor function that is
      automatically called when resources of that type are released (by either
      the garbage collector or <c>enif_release_resource</c>). Resource types
      are uniquely identified by a supplied name string and the name of the
      implementing module.</p>
      <marker id="enif_resource_example"/><p>Here is a template example of how to create and return a resource object.</p>
      <p/>
      <code type="none">
    ERL_NIF_TERM term;
    MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct));

    /* initialize struct ... */

    term = enif_make_resource(env, obj);

    if (keep_a_reference_of_our_own) {
        /* store 'obj' in static variable, private data or other resource object */
    }
    else {
        enif_release_resource(obj);
        /* resource now only owned by "Erlang" */
    }
    return term;
    </code>
      <p>Note that once <c>enif_make_resource</c> creates the term to
      return to Erlang, the code can choose to either keep its own
      native pointer to the allocated struct and release it later, or
      release it immediately and rely solely on the garbage collector
      to eventually deallocate the resource object when it collects
      the term.</p> 
      <p>Another usage of resource objects is to create binary terms with
      user defined memory management.
      <seealso marker="#enif_make_resource_binary">enif_make_resource_binary</seealso>
      will create a binary term that is connected to a resource object. The
      destructor of the resource will be called when the binary is garbage
      collected, at which time the binary data can be released. An example of
      this can be a binary term consisting of data from a <c>mmap</c>'ed file.
      The destructor can then do <c>munmap</c> to release the memory
      region.</p>
      <p>Resource types support upgrade in runtime by allowing a loaded NIF
      library to takeover an already existing resource type and thereby
      "inherit" all existing objects of that type. The destructor of the new
      library will thereafter be called for the inherited objects and the
      library with the old destructor function can be safely unloaded. Existing
      resource objects, of a module that is upgraded, must either be deleted
      or taken over by the new NIF library. The unloading of a library will be
      postponed as long as there exist resource objects with a destructor
      function in the library.
      </p>
      </item>
      <tag>Threads and concurrency</tag>
      <item><p>A NIF is thread-safe without any explicit synchronization as
      long as it acts as a pure function and only reads the supplied
      arguments. As soon as you write towards a shared state either through
      static variables or <seealso marker="#enif_priv_data">enif_priv_data</seealso>
      you need to supply your own explicit synchronization. This includes terms
      in process independent environments that are shared between threads.
      Resource objects will also require synchronization if you treat them as
      mutable.</p>
      <p>The library initialization callbacks <c>load</c>, <c>reload</c> and
      <c>upgrade</c> are all thread-safe even for shared state data.</p>
      </item>

      <tag><marker id="version_management"/>Version Management</tag>
      <item><p>
      When a NIF library is built, information about NIF API version
      is compiled into the library. When a NIF library is loaded the
      runtime system verifies that the library is of a compatible version.
      <c>erl_nif.h</c> defines <c>ERL_NIF_MAJOR_VERSION</c>, and
      <c>ERL_NIF_MINOR_VERSION</c>. <c>ERL_NIF_MAJOR_VERSION</c> will be
      incremented when NIF library incompatible changes are made to the
      Erlang runtime system. Normally it will suffice to recompile the NIF
      library when the <c>ERL_NIF_MAJOR_VERSION</c> has changed, but it
      could, under rare circumstances, mean that NIF libraries have to
      be slightly modified. If so, this will of course be documented.
      <c>ERL_NIF_MINOR_VERSION</c> will be incremented when
      new features are added. The runtime system uses the minor version
      to determine what features to use.
      </p><p>
      The runtime system will normally refuse to load a NIF library if
      the major versions differ, or if the major versions are equal and
      the minor version used by the NIF library is greater than the one
      used by the runtime system. Old NIF libraries with lower major
      versions will however be allowed after a bump of the major version
      during a transition period of two major releases. Such old NIF
      libraries might however fail if deprecated features are used.
      </p></item>

      <tag><marker id="time_measurement"/>Time Measurement</tag>
      <item><p>Support for time measurement in NIF libraries:</p>
      <list>
	<item><seealso marker="#ErlNifTime"><c>ErlNifTime</c></seealso></item>
	<item><seealso marker="#ErlNifTimeUnit"><c>ErlNifTimeUnit</c></seealso></item>
	<item><seealso marker="#enif_monotonic_time"><c>enif_monotonic_time()</c></seealso></item>
	<item><seealso marker="#enif_time_offset"><c>enif_time_offset()</c></seealso></item>
	<item><seealso marker="#enif_convert_time_unit"><c>enif_convert_time_unit()</c></seealso></item>
      </list>
      </item>

      <tag><marker id="lengthy_work"/>Long-running NIFs</tag>

      <item><p>
	As mentioned in the <seealso marker="#WARNING">warning</seealso> text at
	the beginning of this document it is of <em>vital importance</em> that a 
	native function return relatively quickly. It is hard to give an exact
	maximum amount of time that a native function is allowed to work, but as a
	rule of thumb a well-behaving native function should return to its caller
	before a millisecond has passed. This can be achieved using different
	approaches. If you have full control over the code to execute in the
	native function, the best approach is to divide the work into multiple
	chunks of work and call the native function multiple times. In some
	cases this might however not always be possible, e.g. when calling
	third-party libraries.</p>
	
	<p>The
	<seealso marker="#enif_consume_timeslice">enif_consume_timeslice()</seealso>
	function can be used to inform the runtime system about the length of the
	NIF call. It should typically always be used unless the NIF executes very
	quickly.</p>

	<p>If the NIF call is too lengthy one needs to handle this in one of the
	following ways in order to avoid degraded responsiveness, scheduler load
	balancing problems, and other strange behaviors:</p>

	<taglist>
	  <tag>Yielding NIF</tag>
	  <item>
	    <p>
	      If the functionality of a long-running NIF can be split so that
	      its work can be achieved through a series of shorter NIF calls,
	      the application can either make that series of NIF calls from the
	      Erlang level, or it can call a NIF that first performs a chunk of
	      the work, then invokes the
	      <seealso marker="#enif_schedule_nif">enif_schedule_nif</seealso>
	      function to schedule another NIF call to perform the next chunk.
	      The final call scheduled in this manner can then return the
	      overall result. Breaking up a long-running function in
	      this manner enables the VM to regain control between calls to the
	      NIFs.
	    </p>
	    <p>
	      This approach is always preferred over the other alternatives
	      described below. This both from a performance perspective and
	      a system characteristics perspective.
	    </p>
	  </item>

	  <tag>Threaded NIF</tag>
	  <item>
	    <p>
	      This is accomplished by dispatching the work to another thread
	      managed by the NIF library, return from the NIF, and wait for the
	      result. The thread can send the result back to the Erlang
	      process using <seealso marker="#enif_send">enif_send</seealso>.
	      Information about thread primitives can be found below.
	    </p>
	  </item>

	  <tag><marker id="dirty_nifs"/>Dirty NIF</tag>
	  <item>

	    <note>
	      <p>
		<em>The dirty NIF functionality described here
		is experimental</em>. Dirty NIF support is available only when
		the emulator is configured with dirty schedulers enabled. This
		feature is currently disabled by default. The Erlang runtime
		without SMP support do not support dirty schedulers even when
		the dirty scheduler support has been enabled. To check at
		runtime for the presence of dirty scheduler threads, code can
		use the
		<seealso marker="#enif_system_info"><c>enif_system_info()</c></seealso>
		API function.
	      </p>
	    </note>

	    <p>
	      A NIF that cannot be split and cannot execute in a millisecond or
	      less is called a "dirty NIF" because it performs work that the
	      ordinary schedulers of the Erlang runtime system cannot handle cleanly.
	      Applications that make use of such functions must indicate to the
	      runtime that the functions are dirty so they can be handled
	      specially. This is handled by executing dirty jobs on a separate
	      set of schedulers called dirty schedulers. A dirty NIF executing
	      on a dirty scheduler does not have the same duration restriction
	      as a normal NIF.
	    </p>

	    <p>
	      It is important to classify the dirty job correct. An I/O bound
	      job should be classified as such, and a CPU bound job should be
	      classified as such. If you should classify CPU bound jobs
	      as I/O bound jobs, dirty I/O schedulers might starve ordinary
	      schedulers. I/O bound jobs are expected to either block waiting
	      for I/O, and/or spend a limited amount of time moving data.
	    </p>

	    <p>
	      To schedule a dirty NIF for execution, the appropriate
	      <c>flags</c> value can be set for the NIF in its
	      <seealso marker="#ErlNifFunc"><c>ErlNifFunc</c></seealso>
	      entry, or the application can call
	      <seealso marker="#enif_schedule_nif"><c>enif_schedule_nif</c></seealso>,
	      passing to it a pointer to the dirty NIF to be executed and
	      indicating with the <c>flags</c> argument whether it expects the
	      operation to be CPU-bound or I/O-bound. A job that alternates
	      between I/O bound and CPU bound can be reclassified and
	      rescheduled using <c>enif_schedule_nif</c> so that it executes on
	      the correct type of dirty scheduler at all times. For more
	      information see the documentation of the <c>erl</c> command line
	      arguments <seealso marker="erl#+SDcpu"><c>+SDcpu</c></seealso>,
	      and <seealso marker="erl#+SDio"><c>+SDio</c></seealso>.
	    </p>

	    <p>
	      While a process is executing a dirty NIF some operations that
	      communicate with it may take a very long time to complete.
	      Suspend, or garbage collection of a process executing a dirty
	      NIF cannot be done until the dirty NIF has returned, so other
	      processes waiting for such operations to complete might have to
	      wait for a very long time. Blocking multi scheduling, i.e.,
	      calling
	      <seealso marker="erlang#system_flag_multi_scheduling"><c>erlang:system_flag(multi_scheduling,
	      block)</c></seealso>, might also take a very long time to
	      complete. This since all ongoing dirty operations on all
	      dirty schedulers need to complete before the block
	      operation can complete.
	    </p>

	    <p>
	      A lot of operations communicating with a process executing a
	      dirty NIF can, however, complete while it is executing the
	      dirty NIF. For example, retrieving information about it via
	      <c>process_info()</c>, setting its group leader,
	      register/unregister its name, etc.
	    </p>

	    <p>
	      Termination of a process executing a dirty NIF can only be
	      completed up to a certain point while it is executing the
	      dirty NIF. All Erlang resources such as its registered name,
	      its ETS tables, etc will be released. All links and monitors
	      will be triggered. The actual execution of the NIF will
	      however <em>not</em> be stopped. The NIF can safely continue
	      execution, allocate heap memory, etc, but it is of course better
	      to stop executing as soon as possible. The NIF can check
	      whether current process is alive or not using
	      <seealso marker="#enif_is_current_process_alive"><c>enif_is_current_process_alive</c></seealso>.
	      Communication using
	      <seealso marker="#enif_send"><c>enif_send</c></seealso>,
	      and <seealso marker="#enif_port_command"><c>enif_port_command</c></seealso>
	      will also be dropped when the sending process is not alive.
	      Deallocation of certain internal resources such as process
	      heap, and process control block will be delayed until the
	      dirty NIF has completed.
	    </p>

	    <p>Currently known issues that are planned to be fixed:</p>
	    <list>
	      <item>
		<p>
		  Since purging of a module currently might need to garbage
		  collect a process in order to determine if it has
		  references to the module, a process executing a dirty
		  NIF might delay purging for a very long time. Delaying
		  a purge operation implies delaying <em>all</em> code
		  loading operations which might cause severe problems for
		  the system as a whole.
		</p>
	      </item>
	    </list>

	  </item>
	</taglist>

      </item>
    </taglist>
  </section>
  <section>
    <title>INITIALIZATION</title>
    <taglist>
      <tag><marker id="ERL_NIF_INIT"/>ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, reload, upgrade, unload)</tag>
      <item><p>This is the magic macro to initialize a NIF library. It
      should be evaluated in global file scope.</p>
      <p><c>MODULE</c> is the name of the Erlang module as an
      identifier without string quotations. It will be stringified by
      the macro.</p>
      <p><c>funcs</c> is a static array of function descriptors for
      all the implemented NIFs in this library.</p>
      <p><c>load</c>, <c>reload</c>, <c>upgrade</c> and <c>unload</c>
      are pointers to functions. One of <c>load</c>, <c>reload</c> or
      <c>upgrade</c> will be called to initialize the library.
      <c>unload</c> is called to release the library. They are all
      described individually below.</p>
      <p>If compiling a nif for static inclusion via --enable-static-nifs you
      have to define STATIC_ERLANG_NIF before the ERL_NIF_INIT declaration.</p>
      </item>

      <tag><marker id="load"/>int (*load)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)</tag>
       <item><p><c>load</c> is called when the NIF library is loaded
        and there is no previously loaded library for this module.</p>
        <p><c>*priv_data</c> can be set to point to some private data
           that the library needs in order to keep a state between NIF
           calls. <c>enif_priv_data</c> will return this pointer.
           <c>*priv_data</c> will be initialized to NULL when <c>load</c> is
           called.</p> 
        <p><c>load_info</c> is the second argument to <seealso
           marker="erlang#load_nif-2">erlang:load_nif/2</seealso>.</p>
        <p>The library will fail to load if <c>load</c> returns
           anything other than 0. <c>load</c> can be NULL in case no
           initialization is needed.</p> 
       </item>

      <tag><marker id="upgrade"/>int (*upgrade)(ErlNifEnv* env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info)</tag>
       <item><p><c>upgrade</c> is called when the NIF library is loaded
        and there is old code of this module with a loaded NIF library.</p>
        <p>Works the same as <c>load</c>. The only difference is that
        <c>*old_priv_data</c> already contains the value set by the
         last call to <c>load</c> or <c>reload</c> for the old module
         code. <c>*priv_data</c> will be initialized to NULL when <c>upgrade</c>
         is called. It is allowed to write to both *priv_data and *old_priv_data.</p> 
        <p>The library will fail to load if <c>upgrade</c> returns
           anything other than 0 or if <c>upgrade</c> is NULL.</p>
      </item>

      <tag><marker id="unload"/>void (*unload)(ErlNifEnv* env, void* priv_data)</tag>
       <item><p><c>unload</c> is called when the module code that
       the NIF library belongs to is purged as old. New code
       of the same module may or may not exist. Note that <c>unload</c> is not
       called for a replaced library as a consequence of <c>reload</c>.</p>
      </item>

      <tag><marker id="reload"/>int (*reload)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)</tag>
     
       <item>
         <note><p>The reload mechanism is <em>deprecated</em>. It was only intended
         as a development feature. Do not use it as an upgrade method for
         live production systems. It might be removed in future releases. Be sure
         to pass <c>reload</c> as <c>NULL</c> to <seealso marker="#ERL_NIF_INIT">ERL_NIF_INIT</seealso>
         to disable it when not used.</p>
         </note>
        <p><c>reload</c> is called when the NIF library is loaded
        and there is already a previously loaded library for this
        module code.</p>
        <p>Works the same as <c>load</c>. The only difference is that
        <c>*priv_data</c> already contains the value set by the
        previous call to <c>load</c> or <c>reload</c>.</p>
        <p>The library will fail to load if <c>reload</c> returns
           anything other than 0 or if <c>reload</c> is NULL.</p> 
      </item>

    </taglist>
  </section>

  <section>
    <title>DATA TYPES</title>

    <taglist>
      <tag><marker id="ERL_NIF_TERM"/>ERL_NIF_TERM</tag>
       <item>
        <p>Variables of type <c>ERL_NIF_TERM</c> can refer to any Erlang term.
        This is an opaque type and values of it can only by used either as
        arguments to API functions or as return values from NIFs. All
        <c>ERL_NIF_TERM</c>'s belong to an environment
        (<seealso marker="#ErlNifEnv">ErlNifEnv</seealso>). A term can not be
        destructed individually, it is valid until its environment is destructed.</p>
      </item>
     <tag><marker id="ErlNifEnv"/>ErlNifEnv</tag>
      <item>
        <p><c>ErlNifEnv</c> represents an environment that can host Erlang terms.
        All terms in an environment are valid as long as the environment is valid.
        <c>ErlNifEnv</c> is an opaque type and pointers to it can only be passed
        on to API functions. There are two types of environments; process
        bound and process independent.</p>
        <p>A <em>process bound environment</em> is passed as the first argument to all NIFs.
        All function arguments passed to a NIF will belong to that environment.
        The return value from a NIF must also be a term belonging to the same
        environment.
        In addition a process bound environment contains transient information
        about the calling Erlang process. The environment is only valid in the 
        thread where it was supplied as argument until the NIF returns. It is
        thus useless and dangerous to store pointers to process bound
        environments between NIF calls. </p>
        <p>A <em>process independent environment</em> is created by calling
        <seealso marker="#enif_alloc_env">enif_alloc_env</seealso>. It can be
        used to store terms between NIF calls and to send terms with
        <seealso marker="#enif_send">enif_send</seealso>. A process
        independent environment with all its terms is valid until you explicitly
        invalidates it with <seealso marker="#enif_free_env">enif_free_env</seealso>
        or <c>enif_send</c>.</p>
        <p>All contained terms of a list/tuple/map must belong to the same
	environment as the list/tuple/map itself. Terms can be copied between
	environments with
        <seealso marker="#enif_make_copy">enif_make_copy</seealso>.</p>
      </item>
    <tag><marker id="ErlNifFunc"/>ErlNifFunc</tag>
     <item>
      <p/>
      <code type="none">
typedef struct {
    const char* name;
    unsigned arity;
    ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
    unsigned flags;
} ErlNifFunc;
</code>
        <p>Describes a NIF by its name, arity and implementation.
        <c>fptr</c> is a pointer to the function that implements the
        NIF. The argument <c>argv</c> of a NIF will contain the
        function arguments passed to the NIF and <c>argc</c> is the
        length of the array, i.e. the function arity. <c>argv[N-1]</c>
        will thus denote the Nth argument to the NIF. Note that the
        <c>argc</c> argument allows for the same C function to
        implement several Erlang functions with different arity (but
        same name probably). For a regular NIF, <c>flags</c> is 0 (and
        so its value can be omitted for statically initialized <c>ErlNifFunc</c>
        instances), or it can be used to indicate that the NIF is a <seealso
        marker="#dirty_nifs">dirty NIF</seealso> that should be executed
        on a dirty scheduler thread (<em>note that the dirty NIF functionality
        described here is experimental</em> and that you have to enable
        support for dirty schedulers when building OTP in order to try the
        functionality out). If the dirty NIF is expected to be
        CPU-bound, its <c>flags</c> field should be set to
        <c>ERL_NIF_DIRTY_JOB_CPU_BOUND</c>, or for I/O-bound jobs,
        <c>ERL_NIF_DIRTY_JOB_IO_BOUND</c>.</p>
	<note><p>If one of the
	<c>ERL_NIF_DIRTY_JOB_*_BOUND</c> flags is set, and the runtime
	system has no support for dirty schedulers, the runtime system
	will refuse to load the NIF library.</p></note>
      </item>
    <tag><marker id="ErlNifBinary"/>ErlNifBinary</tag>
     <item>
      <p/>
      <code type="none">
typedef struct {
    unsigned size;
    unsigned char* data;
} ErlNifBinary;
</code>
        <p><c>ErlNifBinary</c> contains transient information about an
          inspected binary term. <c>data</c> is a pointer to a buffer
          of <c>size</c> bytes with the raw content of the binary.</p>
          <p>Note that <c>ErlNifBinary</c> is a semi-opaque type and you are
          only allowed to read fields <c>size</c> and <c>data</c>.</p>
      </item>

      <tag><marker id="ErlNifBinaryToTerm"/>ErlNifBinaryToTerm</tag>
      <item>
        <p>An enumeration of the options that can be given to
        <seealso marker="#enif_binary_to_term">enif_binary_to_term</seealso>.
	For default behavior, use the value <c>0</c>.</p>
        <taglist>
	  <tag><c>ERL_NIF_BIN2TERM_SAFE</c></tag>
	  <item><p>Use this option when receiving data from untrusted sources.</p></item>
	</taglist>
      </item>

      <tag><marker id="ErlNifPid"/>ErlNifPid</tag>
       <item>
          <p><c>ErlNifPid</c> is a process identifier (pid). In contrast to
          pid terms (instances of <c>ERL_NIF_TERM</c>), <c>ErlNifPid</c>'s are self
          contained and not bound to any
          <seealso marker="#ErlNifEnv">environment</seealso>. <c>ErlNifPid</c>
          is an opaque type.</p>
        </item>
      <tag><marker id="ErlNifPort"/>ErlNifPort</tag>
       <item>
          <p><c>ErlNifPort</c> is a port identifier. In contrast to
          port id terms (instances of <c>ERL_NIF_TERM</c>), <c>ErlNifPort</c>'s are self
          contained and not bound to any
          <seealso marker="#ErlNifEnv">environment</seealso>. <c>ErlNifPort</c>
          is an opaque type.</p>
        </item>

      <tag><marker id="ErlNifResourceType"/>ErlNifResourceType</tag>
       <item>
          <p>Each instance of <c>ErlNifResourceType</c> represent a class of
          memory managed resource objects that can be garbage collected.
          Each resource type has a unique name and a destructor function that
          is called when objects of its type are released.</p>
        </item>
        <tag><marker id="ErlNifResourceDtor"/>ErlNifResourceDtor</tag>
         <item>
           <p/>
           <code type="none">
typedef void ErlNifResourceDtor(ErlNifEnv* env, void* obj);
</code>
            <p>The function prototype of a resource destructor function.</p>
          </item>
          <tag><marker id="ErlNifCharEncoding"/>ErlNifCharEncoding</tag>
           <item>
             <p/>
             <code type="none">
typedef enum {
    ERL_NIF_LATIN1
}ErlNifCharEncoding;
</code>
              <p>The character encoding used in strings and atoms. The only
              supported encoding is currently <c>ERL_NIF_LATIN1</c> for
              iso-latin-1 (8-bit ascii).</p>
            </item>
            <tag><marker id="ErlNifSysInfo"/>ErlNifSysInfo</tag>
             <item>
                <p>Used by <seealso marker="#enif_system_info">enif_system_info</seealso>
                to return information about the runtime system. Contains currently
                the exact same content as <seealso marker="erl_driver#ErlDrvSysInfo">ErlDrvSysInfo</seealso>.</p>
              </item>
              <tag><marker id="ErlNifSInt64"/>ErlNifSInt64</tag>
               <item><p>A native signed 64-bit integer type.</p></item>
              <tag><marker id="ErlNifUInt64"/>ErlNifUInt64</tag>
               <item><p>A native unsigned 64-bit integer type.</p></item>
	       
      <tag><marker id="ErlNifTime"/>ErlNifTime</tag>
      <item>
        <p>A signed 64-bit integer type for representation of time.</p>
      </item>
      <tag><marker id="ErlNifTimeUnit"/>ErlNifTimeUnit</tag>
      <item>
        <p>An enumeration of time units supported by the NIF API:</p>
	<taglist>
	  <tag><c>ERL_NIF_SEC</c></tag>
	  <item><p>Seconds</p></item>
	  <tag><c>ERL_NIF_MSEC</c></tag>
	  <item><p>Milliseconds</p></item>
	  <tag><c>ERL_NIF_USEC</c></tag>
	  <item><p>Microseconds</p></item>
	  <tag><c>ERL_NIF_NSEC</c></tag>
	  <item><p>Nanoseconds</p></item>
	</taglist>
      </item>

      <tag><marker id="ErlNifUniqueInteger"/>ErlNifUniqueInteger</tag>
      <item>
        <p>An enumeration of the properties that can be requested from
        <seealso marker="#enif_make_unique_integer">enif_unique_integer</seealso>.
	For default properties, use the value <c>0</c>.</p>
        <taglist>
	  <tag><c>ERL_NIF_UNIQUE_POSITIVE</c></tag>
	  <item><p>Return only positive integers</p></item>
	  <tag><c>ERL_NIF_UNIQUE_MONOTONIC</c></tag>
	  <item><p>Return only
	  <seealso marker="time_correction#Strictly_Monotonically_Increasing">strictly
	  monotonically increasing</seealso> integer corresponding to creation time</p></item>
	</taglist>
      </item>

    </taglist>
  </section>

  <funcs>
    <func><name><ret>void *</ret><nametext>enif_alloc(size_t size)</nametext></name>
      <fsummary>Allocate dynamic memory</fsummary>
      <desc><p>Allocate memory of <c>size</c> bytes. Return NULL if allocation failed.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_alloc_binary(size_t size, ErlNifBinary* bin)</nametext></name>
      <fsummary>Create a new binary</fsummary>
      <desc><p>Allocate a new binary of size <c>size</c>
      bytes. Initialize the structure pointed to by <c>bin</c> to
      refer to the allocated binary. The binary must either be released by 
      <seealso marker="#enif_release_binary">enif_release_binary</seealso> 
      or ownership transferred to an Erlang term with 
      <seealso marker="#enif_make_binary">enif_make_binary</seealso>. 
      An allocated (and owned) <c>ErlNifBinary</c> can be kept between NIF
      calls.</p>
        <p>Return true on success or false if allocation failed.</p>
      </desc>
    </func>
    <func><name><ret>ErlNifEnv *</ret><nametext>enif_alloc_env()</nametext></name>
      <fsummary>Create a new environment</fsummary>
      <desc><p>Allocate a new process independent environment. The environment can
      be used to hold terms that is not bound to any process. Such terms can
      later be copied to a process environment with
      <seealso marker="#enif_make_copy">enif_make_copy</seealso>
      or be sent to a process as a message with <seealso marker="#enif_send">enif_send</seealso>.</p>
      <p>Return pointer to the new environment.</p>
      </desc>
    </func>
    <func><name><ret>void *</ret><nametext>enif_alloc_resource(ErlNifResourceType* type, unsigned size)</nametext></name>
      <fsummary>Allocate a memory managed resource object</fsummary>
      <desc><p>Allocate a memory managed resource object of type <c>type</c> and size <c>size</c> bytes.</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_clear_env(ErlNifEnv* env)</nametext></name>
      <fsummary>Clear an environment for reuse</fsummary>
      <desc><p>Free all terms in an environment and clear it for reuse. The environment must
      have been allocated with <seealso marker="#enif_alloc_env">enif_alloc_env</seealso>.
      </p></desc>
    </func>
    <func><name><ret>size_t</ret><nametext>enif_binary_to_term(ErlNifEnv *env, const unsigned char* data, size_t size, ERL_NIF_TERM *term, ErlNifBinaryToTerm opts)</nametext></name>
    <fsummary>Create a term from the external format</fsummary>
    <desc>
      <p>Create a term that is the result of decoding the binary data
      at <c>data</c>, which must be encoded according to the Erlang external term format.
      No more than <c>size</c> bytes are read from <c>data</c>. Argument <c>opts</c>
      correspond to the second argument to <seealso marker="erlang#binary_to_term-2">
      <c>erlang:binary_to_term/2</c></seealso>, and must be either <c>0</c> or
      <c>ERL_NIF_BIN2TERM_SAFE</c>.</p>
      <p>On success, store the resulting term at <c>*term</c> and return
      the actual number of bytes read. Return zero if decoding fails or if <c>opts</c>
      is invalid.</p>
      <p>See also:
        <seealso marker="#ErlNifBinaryToTerm"><c>ErlNifBinaryToTerm</c></seealso>,
        <seealso marker="erlang#binary_to_term-2"><c>erlang:binary_to_term/2</c></seealso> and
        <seealso marker="#enif_term_to_binary"><c>enif_term_to_binary</c></seealso>.
      </p>
    </desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_compare(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)</nametext></name>
      <fsummary>Compare two terms</fsummary>
      <desc><p>Return an integer less than, equal to, or greater than
      zero if <c>lhs</c> is found, respectively, to be less than,
      equal, or greater than <c>rhs</c>. Corresponds to the Erlang
      operators <c>==</c>, <c>/=</c>, <c>=&lt;</c>, <c>&lt;</c>,
      <c>&gt;=</c> and <c>&gt;</c> (but <em>not</em> <c>=:=</c> or <c>=/=</c>).</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_broadcast(ErlNifCond *cnd)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_broadcast">erl_drv_cond_broadcast</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ErlNifCond *</ret><nametext>enif_cond_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_create">erl_drv_cond_create</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_destroy(ErlNifCond *cnd)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_destroy">erl_drv_cond_destroy</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_signal(ErlNifCond *cnd)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_signal">erl_drv_cond_signal</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_wait(ErlNifCond *cnd, ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_wait">erl_drv_cond_wait</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_consume_timeslice(ErlNifEnv *env, int percent)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Give the runtime system a hint about how much CPU time the current NIF call has consumed
    since last hint, or since the start of the NIF if no previous hint has been given.
    The time is given as a <c>percent</c> of the timeslice that a process is allowed to execute Erlang
    code until it may be suspended to give time for other runnable processes.
    The scheduling timeslice is not an exact entity, but can usually be
    approximated to about 1 millisecond.</p>
    <p>Note that it is up to the runtime system to determine if and how to use this information.
    Implementations on some platforms may use other means in order to determine consumed
    CPU time. Lengthy NIFs should regardless of this frequently call <c>enif_consume_timeslice</c>
    in order to determine if it is allowed to continue execution or not.</p>

    <p>Returns 1 if the timeslice is exhausted, or 0 otherwise. If 1 is returned the NIF should return
    as soon as possible in order for the process to yield.</p>
    <p>Argument <c>percent</c> must be an integer between 1 and 100. This function
    must only be called from a NIF-calling thread and argument <c>env</c> must be
    the environment of the calling process.</p>
    <p>This function is provided to better support co-operative scheduling, improve system responsiveness,
    and make it easier to prevent misbehaviors of the VM due to a NIF monopolizing a scheduler thread.
    It can be used to divide <seealso marker="#lengthy_work">length work</seealso> into
    a number of repeated NIF-calls without the need to create threads.
    See also the <seealso marker="#WARNING">warning</seealso> text at the beginning of this document.</p>
    </desc>

    </func>

    <func>
      <name><ret>ErlNifTime</ret><nametext>enif_convert_time_unit(ErlNifTime val, ErlNifTimeUnit from, ErlNifTimeUnit to)</nametext></name>
      <fsummary>Convert time unit of a time value</fsummary>
      <desc>
	<marker id="enif_convert_time_unit"></marker>
	<p>Arguments:</p>
	<taglist>
	  <tag><c>val</c></tag>
	  <item>Value to convert time unit for.</item>
	  <tag><c>from</c></tag>
	  <item>Time unit of <c>val</c>.</item>
	  <tag><c>to</c></tag>
	  <item>Time unit of returned value.</item>
	</taglist>
	<p>Converts the <c>val</c> value of time unit <c>from</c> to
	the corresponding value of time unit <c>to</c>. The result is
	rounded using the floor function.</p>
	<p>Returns <c>ERL_NIF_TIME_ERROR</c> if called with an invalid
	time unit argument.</p>
	<p>See also:
	  <seealso marker="#ErlNifTime"><c>ErlNifTime</c></seealso> and
	  <seealso marker="#ErlNifTimeUnit"><c>ErlNifTimeUnit</c></seealso>.
	</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_cpu_time(ErlNifEnv *)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Returns the CPU time in the same format as <seealso marker="erlang#timestamp-0">erlang:timestamp()</seealso>.
        The CPU time is the time the current logical cpu has spent executing since
        some arbitrary point in the past.
        If the OS does not support fetching of this value <c>enif_cpu_time</c>
        invokes <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>.
        </p>
      </desc>
    </func>

    <func><name><ret>int</ret><nametext>enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_equal_tids">erl_drv_equal_tids</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_free(void* ptr)</nametext></name>
      <fsummary>Free dynamic memory</fsummary>
      <desc><p>Free memory allocated by <c>enif_alloc</c>.</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_free_env(ErlNifEnv* env)</nametext></name>
      <fsummary>Free an environment allocated with enif_alloc_env</fsummary>
      <desc><p>Free an environment allocated with <seealso marker="#enif_alloc_env">enif_alloc_env</seealso>.
      All terms created in the environment will be freed as well.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_atom(ErlNifEnv* env, ERL_NIF_TERM term, char* buf, unsigned size, ErlNifCharEncoding encode)</nametext></name>
      <fsummary>Get the text representation of an atom term</fsummary>
      <desc><p>Write a null-terminated string, in the buffer pointed to by
              <c>buf</c> of size <c>size</c>, consisting of the string 
              representation of the atom <c>term</c> with encoding
              <seealso marker="#ErlNifCharEncoding">encode</seealso>. Return
              the number of bytes written (including terminating null character) or 0 if
              <c>term</c> is not an atom with maximum length of 
              <c>size-1</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_atom_length(ErlNifEnv* env, ERL_NIF_TERM term, unsigned* len, ErlNifCharEncoding encode)</nametext></name>
      <fsummary>Get the length of atom <c>term</c></fsummary>
      <desc><p>Set <c>*len</c> to the length (number of bytes excluding
      terminating null character) of the atom <c>term</c> with encoding
      <c>encode</c>. Return true on success or false if <c>term</c> is not an
      atom.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_double(ErlNifEnv* env, ERL_NIF_TERM term, double* dp)</nametext></name>
      <fsummary>Read a floating-point number term</fsummary>
      <desc><p>Set <c>*dp</c> to the floating point value of
      <c>term</c>. Return true on success or false if <c>term</c> is not a float.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_int(ErlNifEnv* env, ERL_NIF_TERM term, int* ip)</nametext></name>
      <fsummary>Read an integer term</fsummary>
      <desc><p>Set <c>*ip</c> to the integer value of
      <c>term</c>. Return true on success or false if <c>term</c> is not an
      integer or is outside the bounds of type <c>int</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_int64(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifSInt64* ip)</nametext></name>
      <fsummary>Read a 64-bit integer term</fsummary>
      <desc><p>Set <c>*ip</c> to the integer value of
      <c>term</c>. Return true on success or false if <c>term</c> is not an
      integer or is outside the bounds of a signed 64-bit integer.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_local_pid(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifPid* pid)</nametext></name>
    <fsummary>Read an local pid term</fsummary>
    <desc><p>If <c>term</c> is the pid of a node local process, initialize the
    pid variable <c>*pid</c> from it and return true. Otherwise return false.
    No check if the process is alive is done.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_local_port(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifPort* port_id)</nametext></name>
    <fsummary>Read an local port term</fsummary>
    <desc><p>If <c>term</c> identifies a node local port, initialize the
    port variable <c>*port_id</c> from it and return true. Otherwise return false.
    No check if the port is alive is done.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_list_cell(ErlNifEnv* env, ERL_NIF_TERM list, ERL_NIF_TERM* head, ERL_NIF_TERM* tail)</nametext></name>
      <fsummary>Get head and tail from a list</fsummary>
      <desc><p>Set <c>*head</c> and <c>*tail</c> from
      <c>list</c> and return true, or return false if <c>list</c> is not a
      non-empty list.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_list_length(ErlNifEnv* env, ERL_NIF_TERM term, unsigned* len)</nametext></name>
      <fsummary>Get the length of list <c>term</c></fsummary>
      <desc><p>Set <c>*len</c> to the length of list <c>term</c> and return true,
      or return false if <c>term</c> is not a proper list.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_long(ErlNifEnv* env, ERL_NIF_TERM term, long int* ip)</nametext></name>
      <fsummary>Read an long integer term</fsummary>
      <desc><p>Set <c>*ip</c> to the long integer value of <c>term</c> and
      return true, or return false if <c>term</c> is not an integer or is
      outside the bounds of type <c>long int</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_map_size(ErlNifEnv* env, ERL_NIF_TERM term, size_t *size)</nametext></name>
      <fsummary>Read the size of a map term</fsummary>
      <desc><p>Set <c>*size</c> to the number of key-value pairs in the map <c>term</c> and
      return true, or return false if <c>term</c> is not a map.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_map_value(ErlNifEnv* env, ERL_NIF_TERM map, ERL_NIF_TERM key, ERL_NIF_TERM* value)</nametext></name>
     <fsummary>Get the value of a key in a map</fsummary>
      <desc><p>Set <c>*value</c> to the value associated with <c>key</c> in the
      map <c>map</c> and return true. Return false if <c>map</c> is not a map
      or if <c>map</c> does not contain <c>key</c>.</p></desc>
    </func>
   <func><name><ret>int</ret><nametext>enif_get_resource(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifResourceType* type, void** objp)</nametext></name>
      <fsummary>Get the pointer to a resource object</fsummary>
      <desc><p>Set <c>*objp</c> to point to the resource object referred to by <c>term</c>.</p>
      <p>Return true on success or false if <c>term</c> is not a handle to a resource object
      of type <c>type</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_string(ErlNifEnv* env, 
                                ERL_NIF_TERM list, char* buf, unsigned size,
                                ErlNifCharEncoding encode)</nametext></name>
      <fsummary>Get a C-string from a list</fsummary>
      <desc><p>Write a null-terminated string, in the buffer pointed to by
              <c>buf</c> with size <c>size</c>, consisting of the characters
              in the string <c>list</c>. The characters are written using encoding
              <seealso marker="#ErlNifCharEncoding">encode</seealso>.
              Return the number of bytes written (including terminating null
              character), or <c>-size</c> if the string was truncated due to
              buffer space, or 0 if <c>list</c> is not a string that can be
              encoded with <c>encode</c> or if <c>size</c> was less than 1.              
              The written string is always null-terminated unless buffer
              <c>size</c> is less than 1.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_tuple(ErlNifEnv* env, ERL_NIF_TERM term, int* arity, const ERL_NIF_TERM** array)</nametext></name>
      <fsummary>Inspect the elements of a tuple</fsummary>
      <desc><p>If <c>term</c> is a tuple, set <c>*array</c> to point
      to an array containing the elements of the tuple and set
      <c>*arity</c> to the number of elements. Note that the array
      is read-only and <c>(*array)[N-1]</c> will be the Nth element of
      the tuple. <c>*array</c> is undefined if the arity of the tuple
      is zero.</p><p>Return true on success or false if <c>term</c> is not a
      tuple.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_uint(ErlNifEnv* env, ERL_NIF_TERM term, unsigned int* ip)</nametext></name>
      <fsummary>Read an unsigned integer term</fsummary>
      <desc><p>Set <c>*ip</c> to the unsigned integer value of <c>term</c> and
      return true, or return false if <c>term</c> is not an unsigned integer or
      is outside the bounds of type <c>unsigned int</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_uint64(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifUInt64* ip)</nametext></name>
      <fsummary>Read an unsigned 64-bit integer term</fsummary>
      <desc><p>Set <c>*ip</c> to the unsigned integer value of <c>term</c> and
      return true, or return false if <c>term</c> is not an unsigned integer or
      is outside the bounds of an unsigned 64-bit integer.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_ulong(ErlNifEnv* env, ERL_NIF_TERM term, unsigned long* ip)</nametext></name>
      <fsummary>Read an unsigned integer term</fsummary>
      <desc><p>Set <c>*ip</c> to the unsigned long integer value of <c>term</c>
      and return true, or return false if <c>term</c> is not an unsigned integer or is
      outside the bounds of type <c>unsigned long</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_getenv(const char* key, char* value, size_t *value_size)</nametext></name>
      <fsummary>Get the value of an environment variable</fsummary>
      <desc><p>Same as <seealso marker="erl_driver#erl_drv_getenv">erl_drv_getenv</seealso>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_has_pending_exception(ErlNifEnv* env, ERL_NIF_TERM* reason)</nametext></name>
      <fsummary>Check if an exception has been raised</fsummary>
      <desc><p>Return true if a pending exception is associated
      with the environment <c>env</c>. If <c>reason</c> is a null pointer, ignore it.
      Otherwise, if there's a pending exception associated with <c>env</c>, set the ERL_NIF_TERM
      to which <c>reason</c> points to the value of the exception's term. For example, if
      <seealso marker="#enif_make_badarg">enif_make_badarg</seealso> is called to set a
      pending <c>badarg</c> exception, a subsequent call to <c>enif_has_pending_exception(env, &amp;reason)</c>
      will set <c>reason</c> to the atom <c>badarg</c>, then return true.</p>
      <p>See also: <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>
      and <seealso marker="#enif_raise_exception">enif_raise_exception</seealso>.</p>
      </desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_inspect_binary(ErlNifEnv* env, ERL_NIF_TERM bin_term, ErlNifBinary* bin)</nametext></name>
      <fsummary>Inspect the content of a binary</fsummary>
      <desc><p>Initialize the structure pointed to by <c>bin</c> with 
              information about the binary term
      <c>bin_term</c>. Return true on success or false if <c>bin_term</c> is not a binary.</p></desc> 
    </func>
    <func><name><ret>int</ret><nametext>enif_inspect_iolist_as_binary(ErlNifEnv* 
                                env, ERL_NIF_TERM term, ErlNifBinary* bin)
                              </nametext></name>
      <fsummary>Inspect the content of an iolist</fsummary>
      <desc><p>Initialize the structure pointed to by <c>bin</c> with one
      continuous buffer with the same byte content as <c>iolist</c>. As with 
      inspect_binary, the data pointed to by <c>bin</c> is transient and does 
      not need to be released. Return true on success or false if <c>iolist</c> is not an
      iolist.</p>
      </desc> 
    </func>
    <func><name><ret>int</ret><nametext>enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is an atom</fsummary>
      <desc><p>Return true if <c>term</c> is an atom.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_binary(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a binary</fsummary>
      <desc><p>Return true if <c>term</c> is a binary</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_current_process_alive(ErlNifEnv* env)</nametext></name>
      <fsummary>Determine if currently executing process is alive or not.</fsummary>
      <desc><p>Return true if currently executing process is currently alive; otherwise
      false.</p>
      <p>This function can only be used from a NIF-calling thread, and with an
      environment corresponding to currently executing processes.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_empty_list(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is an empty list</fsummary>
      <desc><p>Return true if <c>term</c> is an empty list.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_exception(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is an exception</fsummary>
      <desc><marker id="enif_is_exception"/>
        <p>Return true if <c>term</c> is an exception.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_map(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a map</fsummary>
      <desc><p>Return true if <c>term</c> is a map, false otherwise.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_number(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a number (integer or float)</fsummary>
      <desc><p>Return true if <c>term</c> is a number.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_fun(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a fun</fsummary>
      <desc><p>Return true if <c>term</c> is a fun.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_identical(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)</nametext></name>
      <fsummary>Erlang operator =:=</fsummary>
      <desc><p>Return true if the two terms are identical. Corresponds to the
      Erlang operators <c>=:=</c> and
      <c>=/=</c>.</p></desc> 
    </func>
    <func><name><ret>int</ret><nametext>enif_is_pid(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a pid</fsummary>
      <desc><p>Return true if <c>term</c> is a pid.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_port(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a port</fsummary>
      <desc><p>Return true if <c>term</c> is a port.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_port_alive(ErlNifEnv* env, ErlNifPort *port_id)</nametext></name>
      <fsummary>Determine if a local port is alive or not.</fsummary>
      <desc><p>Return true if <c>port_id</c> is currently alive.</p>
      <p>This function is only thread-safe when the emulator with SMP support is used.
      It can only be used in a non-SMP emulator from a NIF-calling thread.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_process_alive(ErlNifEnv* env, ErlNifPid *pid)</nametext></name>
      <fsummary>Determine if a local process is alive or not.</fsummary>
      <desc><p>Return true if <c>pid</c> is currently alive.</p>
      <p>This function is only thread-safe when the emulator with SMP support is used.
      It can only be used in a non-SMP emulator from a NIF-calling thread.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_ref(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a reference</fsummary>
      <desc><p>Return true if <c>term</c> is a reference.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_tuple(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a tuple</fsummary>
      <desc><p>Return true if <c>term</c> is a tuple.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_list(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a list</fsummary>
      <desc><p>Return true if <c>term</c> is a list.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_keep_resource(void* obj)</nametext></name>
      <fsummary>Add a reference to a resource object</fsummary>
      <desc><p>Add a reference to resource object <c>obj</c> obtained from
      <seealso marker="#enif_alloc_resource">enif_alloc_resource</seealso>.
      Each call to <c>enif_keep_resource</c> for an object must be balanced by
      a call to <seealso marker="#enif_release_resource">enif_release_resource</seealso>
      before the object will be destructed.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_atom(ErlNifEnv* env, const char* name)</nametext></name>
      <fsummary>Create an atom term</fsummary>
      <desc><p>Create an atom term from the null-terminated C-string <c>name</c>
      with iso-latin-1 encoding. If the length of <c>name</c> exceeds the maximum length
      allowed for an atom (255 characters), <c>enif_make_atom</c> invokes
      <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>.
      </p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_atom_len(ErlNifEnv* env, const char* name, size_t len)</nametext></name>
      <fsummary>Create an atom term</fsummary>
      <desc><p>Create an atom term from the string <c>name</c> with length <c>len</c>.
      Null-characters are treated as any other characters. If <c>len</c> is greater than the maximum length
      allowed for an atom (255 characters), <c>enif_make_atom</c> invokes
      <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>.
      </p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_badarg(ErlNifEnv* env)</nametext></name>
      <fsummary>Make a badarg exception</fsummary>
      <desc><p>Make a badarg exception to be returned from a NIF, and associate
      it with the environment <c>env</c>. Once a NIF or any function
      it calls invokes <c>enif_make_badarg</c>, the runtime ensures that a
      <c>badarg</c> exception is raised when the NIF returns, even if the NIF
      attempts to return a non-exception term instead.
      The return value from <c>enif_make_badarg</c> may be used only as the
      return value from the NIF that invoked it (directly or indirectly)
      or be passed to
      <seealso marker="#enif_is_exception">enif_is_exception</seealso>, but
      not to any other NIF API function.</p>
      <p>See also: <seealso marker="#enif_has_pending_exception">enif_has_pending_exception</seealso>
      and <seealso marker="#enif_raise_exception">enif_raise_exception</seealso>.
      </p>
      <note><p>In earlier versions (older than erts-7.0, OTP 18) the return value
      from <c>enif_make_badarg</c> had to be returned from the NIF. This
      requirement is now lifted as the return value from the NIF is ignored
      if <c>enif_make_badarg</c> has been invoked.</p></note></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_binary(ErlNifEnv* env, ErlNifBinary* bin)</nametext></name>
      <fsummary>Make a binary term</fsummary>
      <desc><p>Make a binary term from <c>bin</c>. Any ownership of 
              the binary data will be transferred to the created term and
              <c>bin</c> should be considered read-only for the rest of the NIF
              call and then as released.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_copy(ErlNifEnv* dst_env, ERL_NIF_TERM src_term)</nametext></name>
      <fsummary>Make a copy of a term</fsummary>
      <desc><p>Make a copy of term <c>src_term</c>. The copy will be created in
      environment <c>dst_env</c>. The source term may be located in any
      environment.</p></desc>        
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_double(ErlNifEnv* env, double d)</nametext></name>
      <fsummary>Create a floating-point term</fsummary>
      <desc><p>Create a floating-point term from a <c>double</c>. If the <c>double</c> argument is
      not finite or is NaN, <c>enif_make_double</c> invokes
      <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>.
      </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_existing_atom(ErlNifEnv* env, const char* name, ERL_NIF_TERM* atom, ErlNifCharEncoding encode)</nametext></name>
      <fsummary>Create an existing atom term</fsummary>
      <desc><p>Try to create the term of an already existing atom from
      the null-terminated C-string <c>name</c> with encoding
      <seealso marker="#ErlNifCharEncoding">encode</seealso>. If the atom
      already exists store the term in <c>*atom</c> and return true, otherwise
      return false. If the length of <c>name</c> exceeds the maximum length
      allowed for an atom (255 characters), <c>enif_make_existing_atom</c>
      returns false.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_existing_atom_len(ErlNifEnv* env, const char* name, size_t len, ERL_NIF_TERM* atom, ErlNifCharEncoding encoding)</nametext></name>
      <fsummary>Create an existing atom term</fsummary>
      <desc><p>Try to create the term of an already existing atom from the
      string <c>name</c> with length <c>len</c> and encoding
      <seealso marker="#ErlNifCharEncoding">encode</seealso>. Null-characters
      are treated as any other characters. If the atom already exists store the term
      in <c>*atom</c> and return true, otherwise return false. If <c>len</c> is greater
      than the maximum length allowed for an atom (255 characters),
      <c>enif_make_existing_atom_len</c> returns false.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_int(ErlNifEnv* env, int i)</nametext></name>
      <fsummary>Create an integer term</fsummary>
      <desc><p>Create an integer term.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_int64(ErlNifEnv* env, ErlNifSInt64 i)</nametext></name>
      <fsummary>Create an integer term</fsummary>
      <desc><p>Create an integer term from a signed 64-bit integer.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list(ErlNifEnv* env, unsigned cnt, ...)</nametext></name>
      <fsummary>Create a list term</fsummary>
      <desc><p>Create an ordinary list term of length <c>cnt</c>. Expects
      <c>cnt</c> number of arguments (after <c>cnt</c>) of type ERL_NIF_TERM as the
      elements of the list. An empty list is returned if <c>cnt</c> is 0.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list1(ErlNifEnv* env, ERL_NIF_TERM e1)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list2(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list3(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list4(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list5(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list6(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list7(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list8(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list9(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)</nametext></name>
      <fsummary>Create a list term</fsummary>
      <desc><p>Create an ordinary list term with length indicated by the
      function name. Prefer these functions (macros) over the variadic
      <c>enif_make_list</c>  to get a compile time error if the number of
      arguments does not match.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list_cell(ErlNifEnv* env, ERL_NIF_TERM head, ERL_NIF_TERM tail)</nametext></name>
      <fsummary>Create a list cell</fsummary>
      <desc><p>Create a list cell <c>[head | tail]</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list_from_array(ErlNifEnv* env, const ERL_NIF_TERM arr[], unsigned cnt)</nametext></name>
      <fsummary>Create a list term from an array</fsummary>
      <desc><p>Create an ordinary list containing the elements of array <c>arr</c>
      of length <c>cnt</c>. An empty list is returned if <c>cnt</c> is 0.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_long(ErlNifEnv* env, long int i)</nametext></name>
      <fsummary>Create an integer term from a long int</fsummary>
      <desc><p>Create an integer term from a <c>long int</c>.</p></desc>
    </func>
    <func><name><ret>unsigned char *</ret><nametext>enif_make_new_binary(ErlNifEnv* env, size_t size, ERL_NIF_TERM* termp)</nametext></name>
      <fsummary>Allocate and create a new binary term</fsummary>
      <desc><p>Allocate a binary of size <c>size</c> bytes and create an owning
      term. The binary data is mutable until the calling NIF returns. This is a
      quick way to create a new binary without having to use
      <seealso marker="#ErlNifBinary">ErlNifBinary</seealso>. The drawbacks are
      that the binary can not be kept between NIF calls and it can not be
      reallocated.</p><p>Return a pointer to the raw binary data and set
      <c>*termp</c> to the binary term.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_new_map(ErlNifEnv* env)</nametext></name>
      <fsummary>Make an empty map term</fsummary>
      <desc><p>Make an empty map term.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_map_put(ErlNifEnv* env, ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM value, ERL_NIF_TERM* map_out)</nametext></name>
      <fsummary>Insert key-value pair in map</fsummary>
      <desc><p>Make a copy of map <c>map_in</c> and insert <c>key</c> with
      <c>value</c>. If <c>key</c> already exists in <c>map_in</c>, the old
      associated value is replaced by <c>value</c>. If successful set
      <c>*map_out</c> to the new map and return true. Return false if
      <c>map_in</c> is not a map.</p>
      <p>The <c>map_in</c> term must belong to the environment <c>env</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_map_update(ErlNifEnv* env, ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM new_value, ERL_NIF_TERM* map_out)</nametext></name>
      <fsummary>Replace value for key in map</fsummary>
      <desc><p>Make a copy of map <c>map_in</c> and replace the old associated
      value for <c>key</c> with <c>new_value</c>. If successful set
      <c>*map_out</c> to the new map and return true. Return false if
      <c>map_in</c> is not a map or if it does no contain <c>key</c>.</p>
      <p>The <c>map_in</c> term must belong to the environment <c>env</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_map_remove(ErlNifEnv* env, ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM* map_out)</nametext></name>
      <fsummary>Remove key from map</fsummary>
      <desc><p>If map <c>map_in</c> contains <c>key</c>, make a copy of
      <c>map_in</c> in <c>*map_out</c> and remove <c>key</c> and associated
      value. If map <c>map_in</c> does not contain <c>key</c>, set
      <c>*map_out</c> to <c>map_in</c>. Return true for success or false if
      <c>map_in</c> is not a map.</p>
      <p>The <c>map_in</c> term must belong to the environment <c>env</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_pid(ErlNifEnv* env, const ErlNifPid* pid)</nametext></name>
      <fsummary>Make a pid term</fsummary>
      <desc><p>Make a pid term from <c>*pid</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_ref(ErlNifEnv* env)</nametext></name>
      <fsummary>Create a reference</fsummary>
      <desc><p>Create a reference like <seealso marker="erlang#make_ref-0">erlang:make_ref/0</seealso>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_resource(ErlNifEnv* env, void* obj)</nametext></name>
      <fsummary>Create an opaque handle to a resource object</fsummary>
      <desc><p>Create an opaque handle to a memory managed resource object
      obtained by <seealso marker="#enif_alloc_resource">enif_alloc_resource</seealso>.
      No ownership transfer is done, as the resource object still needs to be released by
      <seealso marker="#enif_release_resource">enif_release_resource</seealso>,
      but note that the call to <c>enif_release_resource</c> can occur
      immediately after obtaining the term from <c>enif_make_resource</c>,
      in which case the resource object will be deallocated when the
      term is garbage collected. See the
      <seealso marker="#enif_resource_example">example of creating and
      returning a resource object</seealso> for more details.</p> 
      <p>Note that the only defined behaviour of using a resource term in
      an Erlang program is to store it and send it between processes on the
      same node. Other operations such as matching or <c>term_to_binary</c>
      will have unpredictable (but harmless) results.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_resource_binary(ErlNifEnv* env, void* obj, const void* data, size_t size)</nametext></name>
      <fsummary>Create a custom binary term</fsummary>
      <desc><p>Create a binary term that is memory managed by a resource object
      <c>obj</c> obtained by <seealso marker="#enif_alloc_resource">enif_alloc_resource</seealso>.
      The returned binary term will consist of <c>size</c> bytes pointed to
      by <c>data</c>. This raw binary data must be kept readable and unchanged
      until the destructor of the resource is called. The binary data may be
      stored external to the resource object in which case it is the responsibility
      of the destructor to release the data.</p>
      <p>Several binary terms may be managed by the same resource object. The
      destructor will not be called until the last binary is garbage collected.
      This can be useful as a way to return different parts of a larger binary
      buffer.</p>
      <p>As with <seealso marker="#enif_make_resource">enif_make_resource</seealso>,
      no ownership transfer is done. The resource still needs to be released with
      <seealso marker="#enif_release_resource">enif_release_resource</seealso>.</p>
      </desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_reverse_list(ErlNifEnv* env, ERL_NIF_TERM list_in, ERL_NIF_TERM *list_out)</nametext></name>
      <fsummary>Create the reverse of a list</fsummary>
      <desc><p>Set <c>*list_out</c> to the reverse list of the list <c>list_in</c> and return true,
      or return false if <c>list_in</c> is not a list. This function should only be used on
      short lists as a copy will be created of the list which will not be released until after the
      nif returns.</p>
      <p>The <c>list_in</c> term must belong to the environment <c>env</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_string(ErlNifEnv* env, const char* string, ErlNifCharEncoding encoding)</nametext></name>
      <fsummary>Create a string</fsummary>
      <desc><p>Create a list containing the characters of the
      null-terminated string <c>string</c> with encoding <seealso marker="#ErlNifCharEncoding">encoding</seealso>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_string_len(ErlNifEnv* env, const char* string, size_t len, ErlNifCharEncoding encoding)</nametext></name>
      <fsummary>Create a string</fsummary>
      <desc><p>Create a list containing the characters of the string <c>string</c> with
      length <c>len</c> and encoding <seealso marker="#ErlNifCharEncoding">encoding</seealso>.
      Null-characters are treated as any other characters.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_sub_binary(ErlNifEnv* 
      env, ERL_NIF_TERM bin_term, size_t pos, size_t size)</nametext></name>
      <fsummary>Make a subbinary term</fsummary>
      <desc><p>Make a subbinary of binary <c>bin_term</c>, starting at 
              zero-based position <c>pos</c> with a length of <c>size</c> bytes. 
              <c>bin_term</c> must be a binary or bitstring and
              <c>pos+size</c> must be less or equal to the number of whole
              bytes in <c>bin_term</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple(ErlNifEnv* env, unsigned cnt, ...)</nametext></name>
      <fsummary>Create a tuple term</fsummary>
      <desc><p>Create a tuple term of arity <c>cnt</c>. Expects
      <c>cnt</c> number of arguments (after <c>cnt</c>) of type ERL_NIF_TERM as the
      elements of the tuple.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple1(ErlNifEnv* env, ERL_NIF_TERM e1)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple2(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple3(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple4(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple5(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple6(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple7(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple8(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple9(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)</nametext></name>
      <fsummary>Create a tuple term</fsummary>
      <desc><p>Create a tuple term with length indicated by the
      function name. Prefer these functions (macros) over the variadic
      <c>enif_make_tuple</c>  to get a compile time error if the number of
      arguments does not match.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple_from_array(ErlNifEnv* env, const ERL_NIF_TERM arr[], unsigned cnt)</nametext></name>
      <fsummary>Create a tuple term from an array</fsummary>
      <desc><p>Create a tuple containing the elements of array <c>arr</c>
      of length <c>cnt</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_uint(ErlNifEnv* env, unsigned int i)</nametext></name>
      <fsummary>Create an unsigned integer term</fsummary>
      <desc><p>Create an integer term from an <c>unsigned int</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_uint64(ErlNifEnv* env, ErlNifUInt64 i)</nametext></name>
      <fsummary>Create an unsigned integer term</fsummary>
      <desc><p>Create an integer term from an unsigned 64-bit integer.</p></desc>
    </func>
    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_unique_integer(ErlNifEnv *env, ErlNifUniqueInteger properties)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Returns a unique integer with the same properties as given by <seealso marker="erlang#unique_integer-1">erlang:unique_integer/1</seealso>.</p>
        <p><c>env</c> is the environment to create the integer in.</p>
        <p>
          <c>ERL_NIF_UNIQUE_POSITIVE</c> and <c>ERL_NIF_UNIQUE_MONOTONIC</c> can
          be passed as the second argument to change the properties of the
          integer returned. It is possible to combine them by or:ing the
          two values together.
        </p>
        <p>See also:
	<seealso marker="#ErlNifUniqueInteger"><c>ErlNifUniqueInteger</c></seealso>.
	</p>
      </desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_ulong(ErlNifEnv* env, unsigned long i)</nametext></name>
      <fsummary>Create an integer term from an unsigned long int</fsummary>
      <desc><p>Create an integer term from an <c>unsigned long int</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_map_iterator_create(ErlNifEnv *env, ERL_NIF_TERM map, ErlNifMapIterator *iter, ErlNifMapIteratorEntry entry)</nametext></name>
      <fsummary>Create a map iterator</fsummary>
      <desc><p>Create an iterator for the map <c>map</c> by initializing the
      structure pointed to by <c>iter</c>. The <c>entry</c> argument determines
      the start position of the iterator: <c>ERL_NIF_MAP_ITERATOR_FIRST</c> or
      <c>ERL_NIF_MAP_ITERATOR_LAST</c>. Return true on success or false if
      <c>map</c> is not a map.</p>
      <p>A map iterator is only useful during the lifetime of the environment
      <c>env</c> that the <c>map</c> belongs to. The iterator must be destroyed by
      calling <seealso marker="#enif_map_iterator_destroy">
      enif_map_iterator_destroy</seealso>.</p>
      <code type="none">
ERL_NIF_TERM key, value;
ErlNifMapIterator iter;
enif_map_iterator_create(env, my_map, &amp;iter, ERL_NIF_MAP_ITERATOR_FIRST);

while (enif_map_iterator_get_pair(env, &amp;iter, &amp;key, &amp;value)) {
    do_something(key,value);
    enif_map_iterator_next(env, &amp;iter);
}
enif_map_iterator_destroy(env, &amp;iter);
      </code>
     <note><p>The key-value pairs of a map have no defined iteration
     order. The only guarantee is that the iteration order of a single map
     instance is preserved during the lifetime of the environment that the map
     belongs to.</p>
    </note>
      </desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_map_iterator_destroy(ErlNifEnv *env, ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Destroy a map iterator</fsummary>
      <desc><p>Destroy a map iterator created by
      <seealso marker="#enif_map_iterator_create">enif_map_iterator_create</seealso>.
      </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_map_iterator_get_pair(ErlNifEnv *env, ErlNifMapIterator *iter, ERL_NIF_TERM *key, ERL_NIF_TERM *value)</nametext></name>
      <fsummary>Get key and value at current map iterator position</fsummary>
      <desc><p>Get key and value terms at current map iterator position.
      On success set <c>*key</c> and <c>*value</c> and return true.
      Return false if the iterator is positioned at head (before first entry)
      or tail (beyond last entry).</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_map_iterator_is_head(ErlNifEnv *env, ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Check if map iterator is positioned before first</fsummary>
      <desc><p>Return true if map iterator <c>iter</c> is positioned
      before first entry.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_map_iterator_is_tail(ErlNifEnv *env, ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Check if map iterator is positioned after last</fsummary>
      <desc><p>Return true if map iterator <c>iter</c> is positioned
      after last entry.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_map_iterator_next(ErlNifEnv *env, ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Increment map iterator to point to next entry</fsummary>
      <desc><p>Increment map iterator to point to next key-value entry.
      Return true if the iterator is now positioned at a valid key-value entry,
      or false if the iterator is positioned at the tail (beyond the last
      entry).</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_map_iterator_prev(ErlNifEnv *env, ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Decrement map iterator to point to previous entry</fsummary>
      <desc><p>Decrement map iterator to point to previous key-value entry.
      Return true if the iterator is now positioned at a valid key-value entry,
      or false if the iterator is positioned at the head (before the first
      entry).</p></desc>
    </func>

    <func>
      <name><ret>ErlNifTime</ret><nametext>enif_monotonic_time(ErlNifTimeUnit time_unit)</nametext></name>
      <fsummary>Get Erlang Monotonic Time</fsummary>
      <desc>
	<marker id="enif_monotonic_time"></marker>
	<p>Arguments:</p>
	<taglist>
	  <tag><c>time_unit</c></tag>
	  <item>Time unit of returned value.</item>
	</taglist>
	<p>
	  Returns the current
	  <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang
	  monotonic time</seealso>. Note that it is not uncommon with
	  negative values.
	</p>
	<p>Returns <c>ERL_NIF_TIME_ERROR</c> if called with an invalid
	time unit argument, or if called from a thread that is not a
	scheduler thread.</p>
	<p>See also:
	  <seealso marker="#ErlNifTime"><c>ErlNifTime</c></seealso> and
	  <seealso marker="#ErlNifTimeUnit"><c>ErlNifTimeUnit</c></seealso>.
	</p>
      </desc>
    </func>

    <func><name><ret>ErlNifMutex *</ret><nametext>enif_mutex_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_create">erl_drv_mutex_create</seealso>.
    </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_mutex_destroy(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_destroy">erl_drv_mutex_destroy</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_mutex_lock(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_lock">erl_drv_mutex_lock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_mutex_trylock(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_trylock">erl_drv_mutex_trylock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_mutex_unlock(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_unlock">erl_drv_mutex_unlock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_now_time(ErlNifEnv *env)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Retuns an <seealso marker="erlang#now-0">erlang:now()</seealso> timestamp.
    The enif_now_time function is <em>deprecated</em>.</p></desc>
    </func>
    <func><name><ret>ErlNifResourceType *</ret><nametext>enif_open_resource_type(ErlNifEnv* env,
                             const char* module_str, const char* name,
                             ErlNifResourceDtor* dtor, ErlNifResourceFlags flags, ErlNifResourceFlags* tried)</nametext></name>
      <fsummary>Create or takeover a resource type</fsummary>
      <desc><p>Create or takeover a resource type identified by the string
      <c>name</c> and give it the destructor function pointed to by <seealso marker="#ErlNifResourceDtor">dtor</seealso>.
      Argument <c>flags</c> can have the following values:</p>
      <taglist>
        <tag><c>ERL_NIF_RT_CREATE</c></tag>
              <item>Create a new resource type that does not already exist.</item>
        <tag><c>ERL_NIF_RT_TAKEOVER</c></tag>
              <item>Open an existing resource type and take over ownership of all its instances.
               The supplied destructor <c>dtor</c> will be called both for existing instances
               as well as new instances not yet created by the calling NIF library.</item>            
      </taglist>
      <p>The two flag values can be combined with bitwise-or. The name of the
      resource type is local to the calling module. Argument <c>module_str</c>
      is not (yet) used and must be NULL. The <c>dtor</c> may  be <c>NULL</c>
      in case no destructor is needed.</p>
      <p>On success, return a pointer to the resource type and <c>*tried</c>
      will be set to either <c>ERL_NIF_RT_CREATE</c> or
      <c>ERL_NIF_RT_TAKEOVER</c> to indicate what was actually done.
       On failure, return <c>NULL</c> and set <c>*tried</c> to <c>flags</c>.
       It is allowed to set <c>tried</c> to <c>NULL</c>.</p>
       <p>Note that <c>enif_open_resource_type</c> is only allowed to be called in the three callbacks
       <seealso marker="#load">load</seealso>, <seealso marker="#reload">reload</seealso>
       and <seealso marker="#upgrade">upgrade</seealso>.</p>
      </desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_port_command(ErlNifEnv* env, const ErlNifPort* to_port, ErlNifEnv *msg_env, ERL_NIF_TERM msg)</nametext></name>
      <fsummary>Send a port_command to to_port</fsummary>
      <desc>
        <p>This function works the same as <seealso marker="erlang#port_command-2">erlang:port_command/2</seealso>
        except that it is always completely asynchronous.</p>
        <taglist>
          <tag><c>env</c></tag>
          <item>The environment of the calling process. May not be NULL.</item>
          <tag><c>*to_port</c></tag>
          <item>The port id of the receiving port. The port id should refer to a
          port on the local node.</item>
          <tag><c>msg_env</c></tag>
          <item>The environment of the message term. Can be a process
          independent environment allocated with
          <seealso marker="#enif_alloc_env">enif_alloc_env</seealso> or NULL.</item>
          <tag><c>msg</c></tag>
          <item>The message term to send. The same limitations apply as on the
          payload to <seealso marker="erlang#port_command-2">erlang:port_command/2</seealso>.</item>
        </taglist>
        <p>Using a <c>msg_env</c> of NULL is an optimization which groups together
        calls to <c>enif_alloc_env</c>, <c>enif_make_copy</c>, <c>enif_port_command</c>
        and <c>enif_free_env</c> into one call. This optimization is only usefull
        when a majority of the terms are to be copied from <c>env</c> to the <c>msg_env</c>.</p>
        <p>This function return true if the command was successfully sent; otherwise,
	false. The call may return false if it detects that the command failed for some
	reason. For example, <c>*to_port</c> does not refer to a local port, if currently
	executing process, i.e. the sender, is not alive, or if <c>msg</c> is invalid.</p>
        <p>See also: <seealso marker="#enif_get_local_port"><c>enif_get_local_port</c></seealso>.</p>
      </desc>
    </func>
    <func><name><ret>void *</ret><nametext>enif_priv_data(ErlNifEnv* env)</nametext></name>
      <fsummary>Get the private data of a NIF library</fsummary>
      <desc><p>Return the pointer to the private data that was set by <c>load</c>,
      <c>reload</c> or <c>upgrade</c>.</p>
      <p>Was previously named <c>enif_get_data</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_raise_exception(ErlNifEnv* env, ERL_NIF_TERM reason)</nametext></name>
      <fsummary>Raise a NIF error exception</fsummary>
      <desc><p>Create an error exception with the term <c>reason</c> to be returned from a NIF,
      and associate it with the environment <c>env</c>. Once a NIF or any function it calls
      invokes <c>enif_raise_exception</c>, the runtime ensures that the exception it creates
      is raised when the NIF returns, even if the NIF attempts to return a non-exception
      term instead. The return value from <c>enif_raise_exception</c> may be used only as
      the return value from the NIF that invoked it (directly or indirectly) or be passed
      to <seealso marker="#enif_is_exception">enif_is_exception</seealso>, but
      not to any other NIF API function.</p>
      <p>See also: <seealso marker="#enif_has_pending_exception">enif_has_pending_exception</seealso>
      and <seealso marker="#enif_make_badarg">enif_make_badarg</seealso>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_realloc_binary(ErlNifBinary* bin, size_t size)</nametext></name>
      <fsummary>Change the size of a binary</fsummary>
      <desc><p>Change the size of a binary <c>bin</c>. The source binary
      may be read-only, in which case it will be left untouched and
      a mutable copy is allocated and assigned to <c>*bin</c>. Return true on success,
      false if memory allocation failed.</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_release_binary(ErlNifBinary* bin)</nametext></name>
      <fsummary>Release a binary</fsummary>
      <desc><p>Release a binary obtained from <c>enif_alloc_binary</c>.</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_release_resource(void* obj)</nametext></name>
      <fsummary>Release a resource object</fsummary>
      <desc><p>Remove a reference to resource object <c>obj</c>obtained from
      <seealso marker="#enif_alloc_resource">enif_alloc_resource</seealso>.
      The resource object will be destructed when the last reference is removed.
      Each call to <c>enif_release_resource</c> must correspond to a previous
      call to <c>enif_alloc_resource</c> or
      <seealso marker="#enif_keep_resource">enif_keep_resource</seealso>.
      References made by <seealso marker="#enif_make_resource">enif_make_resource</seealso>
      can only be removed by the garbage collector.</p></desc>
    </func>
    <func><name><ret>ErlNifRWLock *</ret><nametext>enif_rwlock_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_create">erl_drv_rwlock_create</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_destroy(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_destroy">erl_drv_rwlock_destroy</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_rlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rlock">erl_drv_rwlock_rlock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_runlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_runlock">erl_drv_rwlock_runlock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_rwlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rwlock">erl_drv_rwlock_rwlock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_rwunlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rwunlock">erl_drv_rwlock_rwunlock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_rwlock_tryrlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_tryrlock">erl_drv_rwlock_tryrlock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_rwlock_tryrwlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_tryrwlock">erl_drv_rwlock_tryrwlock</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_schedule_nif(ErlNifEnv* env, const char* fun_name, int flags, ERL_NIF_TERM (*fp)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]), int argc, const ERL_NIF_TERM argv[])</nametext></name>
      <fsummary>Schedule a NIF for execution</fsummary>
      <desc>
          <p>Schedule NIF <c>fp</c> to execute. This function allows an application to break up long-running
          work into multiple regular NIF calls or to schedule a <seealso marker="#dirty_nifs">dirty NIF</seealso>
          to execute on a dirty scheduler thread (<em>note that the dirty NIF functionality described here is
          experimental</em> and that you have to enable support for dirty schedulers when building OTP in
          order to try the functionality out).</p>
          <p>The <c>fun_name</c> argument provides a name for the NIF being scheduled for execution. If it cannot
          be converted to an atom, <c>enif_schedule_nif</c> returns a <c>badarg</c> exception.</p>
          <p>The <c>flags</c> argument must be set to 0 for a regular NIF, or if the emulator was built the
          experimental dirty scheduler support enabled, <c>flags</c> can be set to either <c>ERL_NIF_DIRTY_JOB_CPU_BOUND</c>
          if the job is expected to be CPU-bound, or <c>ERL_NIF_DIRTY_JOB_IO_BOUND</c> for jobs that will
          be I/O-bound. If dirty scheduler threads are not available in the emulator, a try to schedule such a job
          will result in a <c>badarg</c> exception.</p>

          <p>The <c>argc</c> and <c>argv</c> arguments can either be the originals passed into the calling NIF, or
          they can be values created by the calling NIF.</p>
          <p>The calling NIF must use the return value of <c>enif_schedule_nif</c> as its own return value.</p>
          <p>Be aware that <c>enif_schedule_nif</c>, as its name implies, only schedules the
          NIF for future execution. The calling NIF does not block waiting for the scheduled NIF to
          execute and return, which means that the calling NIF can't expect to receive the scheduled NIF
          return value and use it for further operations.</p>
      </desc>
    </func>
    <func><name><ret>ErlNifPid *</ret><nametext>enif_self(ErlNifEnv* caller_env, ErlNifPid* pid)</nametext></name>
      <fsummary>Get the pid of the calling process</fsummary>
      <desc><p>Initialize the pid variable <c>*pid</c> to represent the
      calling process. Return <c>pid</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_send(ErlNifEnv* env, ErlNifPid* to_pid, ErlNifEnv* msg_env, ERL_NIF_TERM msg)</nametext></name>
      <fsummary>Send a message to a process</fsummary>
      <desc><p>Send a message to a process.</p>
      <taglist>
        <tag><c>env</c></tag>
              <item>The environment of the calling process. Must be NULL if and
              only if calling from a created thread.</item>
        <tag><c>*to_pid</c></tag>
              <item>The pid of the receiving process. The pid should refer to a process on the local node.</item>
        <tag><c>msg_env</c></tag>
              <item>The environment of the message term. Must be a process
              independent environment allocated with
               <seealso marker="#enif_alloc_env">enif_alloc_env</seealso> or NULL.</item>
        <tag><c>msg</c></tag>
              <item>The message term to send.</item>
      </taglist>
      <p>Return true if the message was successfully sent; otherwise, false. The send
      operation will fail if <c>*to_pid</c> does not refer to an alive local process,
      or if currently executing process, i.e. the sender, is not alive.</p>
      <p>The message environment <c>msg_env</c> with all its terms (including
      <c>msg</c>) will be invalidated by a successful call to <c>enif_send</c>. The environment
      should either be freed with <seealso marker="#enif_free_env">enif_free_env</seealso>
      of cleared for reuse with <seealso marker="#enif_clear_env">enif_clear_env</seealso>.</p>
      <p>If <c>msg_env</c> is set to NULL the <c>msg</c> term is copied and
      the original term and its environemt is still valid after the call.</p>
      <p>This function is only thread-safe when the emulator with SMP support is used.
      It can only be used in a non-SMP emulator from a NIF-calling thread.</p>
      <note><p>Passing <c>msg_env</c> as <c>NULL</c> is only supported since
      erts-8.0 (OTP 19).</p></note>
      </desc>
    </func>
    <func><name><ret>unsigned</ret><nametext>enif_sizeof_resource(void* obj)</nametext></name>
      <fsummary>Get the byte size of a resource object</fsummary>
      <desc><p>Get the byte size of a resource object <c>obj</c> obtained by
      <seealso marker="#enif_alloc_resource">enif_alloc_resource</seealso>.</p></desc>
    </func>

    <func><name><ret>int</ret><nametext>enif_snprintf(char *str, size_t size, const char *format, ...)</nametext></name>
      <fsummary>Format strings and Erlang terms</fsummary>
      <desc>
          <p>Similar to <c>snprintf</c> but this format string also accepts <c>"%T"</c> which formats Erlang terms.
          </p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret><nametext>enif_system_info(ErlNifSysInfo *sys_info_ptr, size_t size)</nametext></name>
      <fsummary>Get information about the Erlang runtime system</fsummary>
      <desc><p>Same as <seealso marker="erl_driver#driver_system_info">driver_system_info</seealso>.
            </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_term_to_binary(ErlNifEnv *env, ERL_NIF_TERM term, ErlNifBinary *bin)</nametext></name>
    <fsummary>Convert a term to the external format</fsummary>
    <desc>
      <p>Allocates a new binary with <seealso marker="#enif_alloc_binary">enif_alloc_binary</seealso>
      and stores the result of encoding <c>term</c> according to the Erlang external term format.</p>
      <p>Returns true on success or false if allocation failed.</p>
      <p>See also:
        <seealso marker="erlang#term_to_binary-1"><c>erlang:term_to_binary/1</c></seealso> and
        <seealso marker="#enif_binary_to_term"><c>enif_binary_to_term</c></seealso>.
      </p>
    </desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_thread_create(char *name,ErlNifTid *tid,void * (*func)(void *),void *args,ErlNifThreadOpts *opts)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_create">erl_drv_thread_create</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_thread_exit(void *resp)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_exit">erl_drv_thread_exit</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_thread_join(ErlNifTid, void **respp)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_join">erl_drv_thread_join </seealso>.
          </p></desc>
    </func>
    <func><name><ret>ErlNifThreadOpts *</ret><nametext>enif_thread_opts_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_opts_create">erl_drv_thread_opts_create</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_thread_opts_destroy(ErlNifThreadOpts *opts)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_opts_destroy">erl_drv_thread_opts_destroy</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ErlNifTid</ret><nametext>enif_thread_self(void)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_self">erl_drv_thread_self</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_thread_type(void)</nametext></name>
        <fsummary>Determine type of current thread</fsummary>
        <desc>
            <p>Determine the type of currently executing thread. A positive value
                indicates a scheduler thread while a negative value or zero indicates
                another type of thread. Currently the following specific types exist
                (which may be extended in the future):</p>
            <taglist>
                <tag><c>ERL_NIF_THR_UNDEFINED</c></tag>
                <item><p>Undefined thread that is not a scheduler thread.</p></item>
                <tag><c>ERL_NIF_THR_NORMAL_SCHEDULER</c></tag>
                <item><p>A normal scheduler thread.</p></item>
                <tag><c>ERL_NIF_THR_DIRTY_CPU_SCHEDULER</c></tag>
                <item><p>A dirty CPU scheduler thread.</p></item>
                <tag><c>ERL_NIF_THR_DIRTY_IO_SCHEDULER</c></tag>
                <item><p>A dirty I/O scheduler thread.</p></item>
            </taglist>
        </desc>
    </func>
    <func>
      <name><ret>ErlNifTime</ret><nametext>enif_time_offset(ErlNifTimeUnit time_unit)</nametext></name>
      <fsummary>Get current Time Offset</fsummary>
      <desc>
	<marker id="enif_time_offset"></marker>
	<p>Arguments:</p>
	<taglist>
	  <tag><c>time_unit</c></tag>
	  <item>Time unit of returned value.</item>
	</taglist>
	<p>Returns the current time offset between
	<seealso marker="time_correction#Erlang_Monotonic_Time">Erlang monotonic time</seealso>
	and
	<seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso>
	converted into the <c>time_unit</c> passed as argument.</p>
	<p>Returns <c>ERL_NIF_TIME_ERROR</c> if called with an invalid
	time unit argument, or if called from a thread that is not a
	scheduler thread.</p>
	<p>See also:
	    <seealso marker="#ErlNifTime"><c>ErlNifTime</c></seealso> and
	    <seealso marker="#ErlNifTimeUnit"><c>ErlNifTimeUnit</c></seealso>.
	</p>
      </desc>
    </func>

    <func><name><ret>int</ret><nametext>enif_tsd_key_create(char *name, ErlNifTSDKey *key)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_key_create">erl_drv_tsd_key_create</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_tsd_key_destroy(ErlNifTSDKey key)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_key_destroy">erl_drv_tsd_key_destroy</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void *</ret><nametext>enif_tsd_get(ErlNifTSDKey key)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_get">erl_drv_tsd_get</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_tsd_set(ErlNifTSDKey key, void *data)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_set">erl_drv_tsd_set</seealso>.
          </p></desc>
    </func>
  </funcs>
  <section>
    <title>SEE ALSO</title>
    <p><seealso marker="erlang#load_nif-2">erlang:load_nif/2</seealso></p>
  </section>
</cref>
