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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | NOTES | COLOPHON |
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SD_EVENT_NEW(3) sd_event_new SD_EVENT_NEW(3)
sd_event_new, sd_event_default, sd_event_ref, sd_event_unref,
sd_event_unrefp, sd_event_get_tid, sd_event - Acquire and release
an event loop object
#include <systemd/sd-event.h>
typedef struct sd_event sd_event;
int sd_event_new(sd_event **event);
int sd_event_default(sd_event **event);
sd_event *sd_event_ref(sd_event *event);
sd_event *sd_event_unref(sd_event *event);
void sd_event_unrefp(sd_event **event);
int sd_event_get_tid(sd_event *event, pid_t *ret);
sd_event_new() allocates a new event loop object. The event loop
object is returned in the event parameter. After use, drop the
returned reference with sd_event_unref(). When the last reference
is dropped, the object is freed.
sd_event_default() acquires a reference to the default event loop
object of the calling thread, possibly allocating a new object if
no default event loop object has been allocated yet for the
thread. After use, drop the returned reference with
sd_event_unref(). When the last reference is dropped, the event
loop is freed. If this function is called while the object
returned from a previous call from the same thread is still
referenced, the same object is returned again, but the reference
is increased by one. It is recommended to use this call instead of
sd_event_new() in order to share event loop objects between
various components that are dispatched in the same thread. All
threads have exactly either zero or one default event loop objects
associated, but never more.
After allocating an event loop object, add event sources to it
with 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_add_defer(3),
sd_event_add_post(3) or sd_event_add_exit(3), and then execute the
event loop using sd_event_loop(3).
sd_event_ref() increases the reference count of the specified
event loop object by one.
sd_event_unref() decreases the reference count of the specified
event loop object by one. If the count hits zero, the object is
freed. Note that it is freed regardless of whether it is the
default event loop object for a thread or not. This means that
allocating an event loop with sd_event_default(), then releasing
it, and then acquiring a new one with sd_event_default() will
result in two distinct objects. Note that, in order to free an
event loop object, all remaining event sources of the event loop
also need to be freed as each keeps a reference to it.
sd_event_unrefp() is similar to sd_event_unref() but takes a
pointer to a pointer to an sd_event object. This call is useful in
conjunction with GCC's and LLVM's Clean-up Variable Attribute[1].
Note that this function is defined as inline function. Use a
declaration like the following, in order to allocate an event loop
object that is freed automatically as the code block is left:
{
__attribute__((cleanup(sd_event_unrefp))) sd_event *event = NULL;
int r;
...
r = sd_event_default(&event);
if (r < 0) {
errno = -r;
fprintf(stderr, "Failed to allocate event loop: %m\n");
}
...
}
sd_event_ref(), sd_event_unref() and sd_event_unrefp() execute no
operation if the passed in event loop object is NULL.
sd_event_get_tid() retrieves the thread identifier ("TID") of the
thread the specified event loop object is associated with. This
call is only supported for event loops allocated with
sd_event_default(), and returns the identifier for the thread the
event loop is the default event loop of. See gettid(2) for more
information on thread identifiers.
On success, sd_event_new(), sd_event_default() and
sd_event_get_tid() return 0 or a positive integer. On failure,
they return a negative errno-style error code. sd_event_ref()
always returns a pointer to the event loop object passed in.
sd_event_unref() always returns NULL.
Errors
Returned errors may indicate the following problems:
-ENOMEM
Not enough memory to allocate the object.
-EMFILE
The maximum number of event loops has been allocated.
-ENXIO
sd_event_get_tid() was invoked on an event loop object that
was not allocated with sd_event_default().
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_new(), sd_event_default(), sd_event_ref(), and
sd_event_unref() were added in version 213.
sd_event_unrefp() and sd_event_get_tid() were added in version
229.
systemd(1), sd-event(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_add_defer(3), sd_event_run(3),
gettid(2)
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
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 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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 258~rc2 SD_EVENT_NEW(3)
Pages that refer to this page: sd-event(3), sd_event_add_child(3), sd_event_add_defer(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_get_fd(3), sd_event_now(3), sd_event_run(3), sd_event_set_signal_exit(3), sd_event_set_watchdog(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 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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