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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | SEE ALSO | COLOPHON |
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SD_EVENT_ADD_DEFER(3) sd_event_add_defer SD_EVENT_ADD_DEFER(3)
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 function will be passed the userdata pointer, which may
be chosen freely by the caller.
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 be
disabled after the invocation, even if the SD_EVENT_ON mode was
requested before.
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.
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.
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
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)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-12-18. (At that
time, the date of the most recent commit that was found in the
repository was 2020-12-18.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 247 SD_EVENT_ADD_DEFER(3)
Pages that refer to this page: sd_bus_set_close_on_exit(3), sd-event(3), sd_event_add_child(3), sd_event_add_inotify(3), sd_event_add_io(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_exit(3), sd_event_new(3), sd_event_run(3), sd_event_set_watchdog(3), sd_event_source_get_event(3), sd_event_source_get_pending(3), sd_event_source_set_description(3), sd_event_source_set_destroy_callback(3), sd_event_source_set_enabled(3), sd_event_source_set_exit_on_failure(3), sd_event_source_set_floating(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_ratelimit(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)
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