sd_event_add_defer(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | SEE ALSO | COLOPHON

SD_EVENT_ADD_DEFER(3)      sd_event_add_defer      SD_EVENT_ADD_DEFER(3)

NAME         top

       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         top

       #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         top

       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.

RETURN VALUE         top

       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.

NOTES         top

       These APIs are implemented as a shared library, which can be
       compiled and linked to with the libsystemd pkg-config(1) file.

SEE ALSO         top

       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)

COLOPHON         top

       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 2021-06-20.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-06-19.)  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 249                                        SD_EVENT_ADD_DEFER(3)

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