SD-EVENT(3) sd-event SD-EVENT(3)
sd-event - A generic event loop implementation
#include <systemd/sd-event.h>
pkg-config --cflags --libs libsystemd
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.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
systemd(1), 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),
epoll(7), timerfd_create(2), signalfd(2), waitid(2)
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 2017-07-05. If you dis‐
cover any rendering problems in this HTML version of the page, or you
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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 234 SD-EVENT(3)
Pages that refer to this page: sd-bus(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_io(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_exit(3), sd_event_get_fd(3), sd_event_new(3), sd_event_now(3), sd_event_run(3), sd_event_set_watchdog(3), sd_event_source_get_event(3), sd_event_source_get_pending(3), sd_event_source_set_description(3), sd_event_source_set_enabled(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), sd_watchdog_enabled(3), systemd.directives(7), systemd.index(7)