x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_EVENT_ADD_DEFER(3) sd_event_add_defer SD_EVENT_ADD_DEFER(3)
NAME
sd_event_add_defer, sd_event_add_post, sd_event_add_exit,
sd_event_handler_t - Add static event sources to an event loop
SYNOPSIS
#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);
DESCRIPTION
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.
RETURN VALUE
On success, these functions return 0 or a positive integer. On failure,
they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-ENOMEM
Not enough memory to allocate an object.
-EINVAL
An invalid argument has been passed.
-ESTALE
The event loop is already terminated.
-ECHILD
The event loop has been created in a different process, library or
module instance.
NOTES
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.
SEE ALSO
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)
systemd 254 SD_EVENT_ADD_DEFER(3)
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