sd-event(3) — Linux manual page

NAME \| SYNOPSIS \| DESCRIPTION \| NOTES \| SEE ALSO \| COLOPHON

SD-EVENT(3)                     sd-event                     SD-EVENT(3)

NAME top

       sd-event - A generic event loop implementation

SYNOPSIS top

       #include <systemd/sd-event.h>

       pkg-config --cflags --libs libsystemd

DESCRIPTION top

       sd-event.h is part of libsystemd(3) and 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_inotify(3),
       sd_event_add_defer(3), sd_event_add_memory_pressure(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_source_set_ratelimit(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_BOOTTIME 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 64-bit 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 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
       started.

COLOPHON top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  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
       man-pages@man7.org

systemd 257~devel                                            SD-EVENT(3)

sd-event(3) — Linux manual page

NAME top

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