Manpages - 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_inotify*(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_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:

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

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).

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

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

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).

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).

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

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_inotify*(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_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), *epoll*(7), *timerfd_create*(2), *signalfd*(2), *waitid*(2)