NAME

       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

       #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);

DESCRIPTION

       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

       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().

NOTES

       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.

HISTORY

       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.

SEE ALSO

       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

        1. Clean-up Variable Attribute
           https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html

systemd 257.4                                                                                    SD_EVENT_NEW(3)