sd-event - Man Page

#include <systemd/sd-event​.h>

pkg-config --cflags --libs libsystemd

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​.

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​.

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