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.Dd March 28, 2012
.Dt CK_HT_INIT 3
.Sh NAME
.Nm ck_ht_init
.Nd initialize a hash table
.Sh LIBRARY
Concurrency Kit (libck, \-lck)
.Sh SYNOPSIS
.In ck_ht.h
.Ft typedef void
.Fn ck_ht_hash_cb_t "ck_ht_hash_t *h" "const void *key" "size_t key_length" "uint64_t seed"
.Ft bool
.Fn ck_ht_init "ck_ht_t *ht" "enum ck_ht_mode mode" "ck_ht_hash_cb_t *hash_function" "struct ck_malloc *allocator" "uint64_t capacity" "uint64_t seed"
.Sh DESCRIPTION
The
.Fn ck_ht_init
function initializes the hash table pointed to by the
.Fa ht
pointer.
.Pp
The argument
.Fa mode
specifies the type of key-value pairs to be stored in the
hash table. The value of
.Fa mode
may be one of:
.Bl -tag -width indent
.It CK_HT_MODE_BYTESTRING
The hash table is meant to store key-value pointers where
key is a region of memory that is up to 65536 bytes long.
This pointer will be dereferenced during hash table operations
for key comparison. Entries of this hash table are expected
to be interacted with using the
.Xr ck_ht_entry_empty 3 ,
.Xr ck_ht_entry_key 3 ,
.Xr ck_ht_entry_key_length 3 ,
.Xr ck_ht_entry_value 3 ,
and
.Xr ck_ht_entry_set 3
functions. Attempting a hash table operation with a key of value
NULL or (void *)UINTPTR_MAX will result in undefined behavior.
.It CK_HT_MODE_DIRECT
The hash table is meant to store key-value pointers where
the key is of fixed width field compatible with the
.Tn uintptr_t
type. The key will be directly compared with other keys for
equality. Entries of this hash table are expected to be interacted
with using the
.Xr ck_ht_entry_empty 3 ,
.Xr ck_ht_entry_key_direct 3 ,
.Xr ck_ht_entry_value_direct 3
and
.Xr ck_entry_set_direct 3
functions. Attempting a hash table operation with a key of value of 0 or
UINTPTR_MAX will result in undefined behavior.
.El
.Pp
In addition to this, the user may bitwise OR the mode flag with
CK_HT_WORKLOAD_DELETE to indicate that the hash table will
have to handle a delete heavy workload, in which case stronger
bounds on latency can be provided at the cost of approximately
13% higher memory usage.
The argument
.Fa hash_function
is a pointer to a user-specified hash function. It is optional,
if
.Dv NULL
is specified, then the default hash function implementation will be
used (
.Xr ck_ht_hash 3 ).
A user-specified hash function takes four arguments. The
.Fa h
argument is a pointer to a hash value object. The hash function
is expected to update the
.Fa value
object of type
.Fa uint64_t
contained with-in the object pointed to by
.Fa h .
The
.Fa key
argument is a pointer to a key, the
.Fa key_length
argument is the length of the key and the
.Fa seed
argument is the initial seed associated with the hash table.
This initial seed is specified by the user in
.Xr ck_ht_init 3 .
.Pp
The
.Fa allocator
argument is a pointer to a structure containing
.Fa malloc
and
.Fa free
function pointers which respectively define the memory allocation and
destruction functions to be used by the hash table being initialized.
.Pp
The argument
.Fa capacity
represents the initial number of key-value pairs the hash
table is expected to contain. This argument is simply a hint
and the underlying implementation is free to allocate more
or less memory than necessary to contain the number of entries
.Fa capacity
specifies.
.Pp
The argument
.Fa seed
specifies the initial seed used by the underlying hash function.
The user is free to choose a value of their choice.
.Pp
The hash table is safe to access by multiple readers in the presence
of one concurrent writer. Behavior is undefined in the presence of
concurrent writers.
.Sh RETURN VALUES
Upon successful completion
.Fn ck_ht_init
returns a value of
.Dv true
and otherwise returns a value of
.Dv false
to indicate an error.
.Sh ERRORS
.Bl -tag -width Er
.Pp
The behavior of
.Fn ck_ht_init
is undefined if
.Fa ht
is not a pointer to a
.Tn ck_ht_t
object.
.El
.Sh SEE ALSO
.Xr ck_ht_stat 3 ,
.Xr ck_ht_destroy 3 ,
.Xr ck_ht_hash 3 ,
.Xr ck_ht_hash_direct 3 ,
.Xr ck_ht_set_spmc 3 ,
.Xr ck_ht_put_spmc 3 ,
.Xr ck_ht_gc 3 ,
.Xr ck_ht_get_spmc 3 ,
.Xr ck_ht_grow_spmc 3 ,
.Xr ck_ht_remove_spmc 3 ,
.Xr ck_ht_reset_spmc 3 ,
.Xr ck_ht_reset_size_spmc 3 ,
.Xr ck_ht_count 3 ,
.Xr ck_ht_entry_empty 3 ,
.Xr ck_ht_entry_key_set 3 ,
.Xr ck_ht_entry_key_set_direct 3 ,
.Xr ck_ht_entry_key 3 ,
.Xr ck_ht_entry_key_length 3 ,
.Xr ck_ht_entry_value 3 ,
.Xr ck_ht_entry_set 3 ,
.Xr ck_ht_entry_set_direct 3 ,
.Xr ck_ht_entry_key_direct 3 ,
.Xr ck_ht_entry_value_direct 3 ,
.Xr ck_ht_iterator_init 3 ,
.Xr ck_ht_next 3
.Pp
Additional information available at http://concurrencykit.org/
