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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | 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 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.
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.
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)
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) 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
[email protected]
systemd 257~devel 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_memory_pressure(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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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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