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)
                           fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));

       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

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

       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

       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_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),

NOTES         top

        1. Clean-up Variable Attribute

COLOPHON         top

       This page is part of the systemd (systemd system and service 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 2020-08-13.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-08-11.)  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

systemd 246                                                  SD_EVENT_NEW(3)

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