SD_EVENT_RUN(3)

  .SH "NAME" sd_event_run, sd_event_loop - Run an event loop
  .SH "SYNOPSIS"

#include <systemd/sd-event.h>

      .HP u int sd_event_run(sd_event *event, uint64_t usec);
      .HP u int sd_event_loop(sd_event *event);

  .SH "DESCRIPTION"

    .PP sd_event_run() may be used to run a single iteration of the event loop specified in the event parameter. The function waits until an event to process is available, and dispatches the registered handler for it. The usec parameter specifies the maximum time (in microseconds) to wait for an event. Use (uint64_t) -1 to specify an infinite timeout.
    .PP sd_event_loop() invokes sd_event_run() in a loop, thus implementing the actual event loop. The call returns as soon as exiting was requested using sd_event_exit(3).
    .PP The event loop object event is created with sd_event_new(3). Events sources to wait for and their handlers may be registered with sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_post(3) and sd_event_add_exit(3).
    .PP For low-level control of event loop execution, use sd_event_prepare(3), sd_event_wait(3) and sd_event_dispatch(3) which are wrapped by sd_event_run(). Along with sd_event_get_fd(3), these functions allow integration of an sd-event(3) event loop into foreign event loop implementations.

  .SH "RETURN VALUE"

    .PP On failure, these functions return a negative errno-style error code. sd_event_run() returns a positive, non-zero integer if an event source was dispatched, and zero when the specified timeout hit before an event source has seen any event, and hence no event source was dispatched. sd_event_loop() returns the exit code specified when invoking sd_event_exit().

  .SH "ERRORS"

    .PP Returned errors may indicate the following problems:

      .PP -EINVAL

            The event parameter is invalid or NULL.
          .RE
          .PP -EBUSY

                The event loop object is not in the right state (see sd_event_prepare(3) for an explanation of possible states).
              .RE
              .PP -ESTALE

                    The event loop is already terminated.
                  .RE
                  .PP -ECHILD

                        The event loop has been created in a different process.
                      .RE

                    .PP Other errors are possible, too.

                  .SH "NOTES"

                  .PP These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.
                  .SH "SEE ALSO"

                    .PP systemd(1), sd-event(3), sd_event_new(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_exit(3), sd_event_get_fd(3), sd_event_wait(3), GLib Main Event Loop[1]

NOTES

1.  GLib Main Event Loop
    https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html