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sd-event(3)

NAME

   sd-event - A generic event loop implementation

SYNOPSIS

   #include <systemd/sd-event.h>

   pkg-config --cflags --libs libsystemd

DESCRIPTION

   sd-event.h provides a generic event loop implementation, based on Linux
   epoll(7).

   See sd_event_new(3), sd_event_run(3), 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_source_unref(3),
   sd_event_source_set_priority(3), sd_event_source_set_enabled(3),
   sd_event_source_set_userdata(3), sd_event_source_get_event(3),
   sd_event_source_get_pending(3), sd_event_source_set_description(3),
   sd_event_source_set_prepare(3), sd_event_wait(3), sd_event_get_fd(3),
   sd_event_set_watchdog(3), sd_event_exit(3), sd_event_now(3) for more
   information about the functions available.

   The event loop design is targeted on running a separate instance of the
   event loop in each thread; it has no concept of distributing events
   from a single event loop instance onto multiple worker threads.
   Dispatching events is strictly ordered and subject to configurable
   priorities. In each event loop iteration a single event source is
   dispatched. Each time an event source is dispatched the kernel is
   polled for new events, before the next event source is dispatched. The
   event loop is designed to honor priorities and provide fairness within
   each priority. It is not designed to provide optimal throughput, as
   this contradicts these goals due the limitations of the underlying
   epoll(7) primitives.

   The event loop implementation provides the following features:

    1. I/O event sources, based on epoll(7)'s file descriptor watching,
       including edge triggered events (EPOLLET). See sd_event_add_io(3).

    2. Timer event sources, based on timerfd_create(2), supporting the
       CLOCK_MONOTONIC, CLOCK_REALTIME, CLOCK_BOOTIME clocks, as well as
       the CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM clocks that can
       resume the system from suspend. When creating timer events a
       required accuracy parameter may be specified which allows
       coalescing of timer events to minimize power consumption. See
       sd_event_add_time(3).

    3. UNIX process signal events, based on signalfd(2), including full
       support for real-time signals, and queued parameters. See
       sd_event_add_signal(3).

    4. Child process state change events, based on waitid(2). See
       sd_event_add_child(3).

    5. Static event sources, of three types: defer, post and exit, for
       invoking calls in each event loop, after other event sources or at
       event loop termination. See sd_event_add_defer(3).

    6. Event sources may be assigned a 64bit priority value, that controls
       the order in which event sources are dispatched if multiple are
       pending simultaneously. See sd_event_source_set_priority(3).

    7. The event loop may automatically send watchdog notification
       messages to the service manager. See sd_event_set_watchdog(3).

    8. The event loop may be integrated into foreign event loops, such as
       the GLib one. See sd_event_get_fd(3) for an example.

NOTES

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

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