sd_event_new(3) — Linux manual page


SD_EVENT_NEW(3)               sd_event_new               SD_EVENT_NEW(3)

NAME         top

       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

SYNOPSIS         top

       #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 *tid);

DESCRIPTION         top

       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.

RETURN VALUE         top

       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.

       Returned errors may indicate the following problems:

           Not enough memory to allocate the object.

           The maximum number of event loops has been allocated.

           sd_event_get_tid() was invoked on an event loop object that
           was not allocated with sd_event_default().

NOTES         top

       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

HISTORY         top

       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

SEE ALSO         top

       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)

NOTES         top

        1. Clean-up Variable Attribute

COLOPHON         top

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       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to

systemd 255                                              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)