sd_event_add_defer, sd_event_add_post, sd_event_add_exit, sd_event_handler_t — Add static event sources to an event loop
#include <systemd/sd-event.h>
typedef struct sd_event_source sd_event_source;
typedef int (*sd_event_handler_t)( | sd_event_source *s, |
void *userdata) ; |
int sd_event_add_defer( | sd_event *event, |
sd_event_source **source, | |
sd_event_handler_t handler, | |
void *userdata) ; |
int sd_event_add_post( | sd_event *event, |
sd_event_source **source, | |
sd_event_handler_t handler, | |
void *userdata) ; |
int sd_event_add_exit( | sd_event *event, |
sd_event_source **source, | |
sd_event_handler_t handler, | |
void *userdata) ; |
These three functions add new static event sources to an event loop. The event loop object is
specified in the event
parameter, the event source object is returned in the
source
parameter. The event sources are enabled statically and will "fire" when
the event loop is run and the conditions described below are met.
The handler
is a function to call or NULL
. The handler
function will be passed the userdata
pointer, which may be chosen freely by the
caller. The handler may return negative to signal an error (see below), other return values are
ignored. If handler
is NULL
, a default handler that calls
sd_event_exit(3) will be
used.
sd_event_add_defer()
adds a new event
source that will be dispatched instantly, before the event loop
goes to sleep again and waits for new events. By default, the
handler will be called once
(SD_EVENT_ONESHOT
). Note that if the event
source is set to SD_EVENT_ON
the event loop
will never go to sleep again, but continuously call the handler,
possibly interleaved with other event sources.
sd_event_add_post()
adds a new event
source that is run before the event loop will sleep and wait
for new events, but only after at least one other non-post event
source was dispatched. By default, the source is enabled
permanently (SD_EVENT_ON
). Note that this
event source type will still allow the event loop to go to sleep
again, even if set to SD_EVENT_ON
, as long as
no other event source is ever triggered.
sd_event_add_exit()
adds a new event
source that will be dispatched when the event loop is terminated
with sd_event_exit(3).
The
sd_event_source_set_enabled(3)
function may be used to enable the event source permanently
(SD_EVENT_ON
) or to make it fire just once
(SD_EVENT_ONESHOT
).
If the handler function returns a negative error code, it will either be disabled after the
invocation, even if the SD_EVENT_ON
mode was requested before, or it will cause the
loop to terminate, see
sd_event_source_set_exit_on_failure(3).
To destroy an event source object use
sd_event_source_unref(3),
but note that the event source is only removed from the event loop
when all references to the event source are dropped. To make sure
an event source does not fire anymore, even when there's still a
reference to it kept, consider setting the event source to
SD_EVENT_OFF
with
sd_event_source_set_enabled(3).
If the second parameter of these functions is passed as NULL
no reference to
the event source object is returned. In this case the event source is considered "floating", and will be
destroyed implicitly when the event loop itself is destroyed.
If the handler
parameter to sd_event_add_defer()
or
sd_event_add_post()
is NULL
, and the event source fires, this
will be considered a request to exit the event loop. In this case, the userdata
parameter, cast to an integer, is passed as the exit code parameter to
sd_event_exit(3). Similar
functionality is not available for sd_event_add_exit()
, as these types of event
sources are only dispatched when exiting anyway.
On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code.
Functions described here are available as a shared
library, which can be compiled against and linked to with the
libsystemd
pkg-config(1)
file.
The code described here uses
getenv(3),
which is declared to be not multi-thread-safe. This means that the code calling the functions described
here must not call
setenv(3)
from a parallel thread. It is recommended to only do calls to setenv()
from an early phase of the program when no other threads have been started.
sd_event_add_defer()
,
sd_event_add_post()
,
sd_event_add_exit()
, and
sd_event_handler_t()
were added in version 217.
systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3), sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3), sd_event_add_inotify(3), sd_event_source_set_enabled(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_set_description(3), sd_event_source_set_floating(3), sd_event_exit(3)