sd_event_wait, sd_event_prepare, sd_event_dispatch — Run parts of libsystemd event loop
#include <systemd/sd-event.h>
int sd_event_prepare( | sd_event *event) ; |
int sd_event_wait( | sd_event *event, |
uint64_t timeout) ; |
int sd_event_dispatch( | sd_event *event) ; |
Functions described here form parts of an event loop.
sd_event_prepare
checks for pending
events and arms necessary timers. If any events are ready to be
processed, it returns a positive value, and the events should be
processed with sd_event_dispatch
.
sd_event_dispatch
runs a handler for one of
the events from the sources with the highest priority. On success,
sd_event_dispatch
returns either 0, which
means that the loop is finished, or a positive value, which means
that the loop is again in the initial state and
sd_event_prepare
should be called again.
In case sd_event_prepare
returned 0,
sd_event_wait
should be called to wait for
events or a timeout. If any events are ready to be processed, it
returns a positive value, and the events should be processed with
sd_event_dispatch
. Otherwise, the loop is
back in the initial state and sd_event_prepare
should be called again.
┌──────────┐ │ initial ├──←←←←←←←←←←←←←←←←←←←─┐ └───┬──────┘ ↑ │ ↑ sd_event_prepare ┌─────────┐ ↑ ├ 0 →→→→→→→──┤ armed │ ↑ 1 └───┬─────┘ ↑ ↓ │ ↑ ↓ sd_event_wait ↑ ├───←←←←←←←─── 1 ┴─ 0 →→→→→→→─┘ ┌───┴──────┐ ↑ │ pending │ ↑ └───┬──────┘ ↑ │ ↑ sd_event_dispatch ↑ ↓ ↑ ├ 1 ──────────→→→→→→→─────────┘ 0 ↓ ┌───┴──────┐ │ finished │ └──────────┘
All three functions as the first argument take the event
loop object event
that is created with with
sd_event_new
. The timeout for
sd_event_wait
is specified with
timeout
in milliseconds.
(uint64_t) -1
may be used to specify an
infinite timeout.
On success, these functions return 0 or a positive integer.
On failure, they return a negative errno-style error code. In case
of sd_event_prepare
and
sd_event_wait
a positive value means that
events are ready to be processed and 0 means that no events are
ready. In case of sd_event_dispatch
a
positive value means that the loop is again in the initial state
and 0 means the loop is finished. For any of those functions, a
negative return value means the loop must be aborted.
Functions described here are available
as a shared library, which can be compiled and linked to with the
libsystemd
pkg-config(1)
file.