sd-event(3)

1SD-EVENT(3)                        sd-event                        SD-EVENT(3)
2
3
4

NAME

6       sd-event - A generic event loop implementation
7

SYNOPSIS

9       #include <systemd/sd-event.h>
10
11       pkg-config --cflags --libs libsystemd
12

DESCRIPTION

14       sd-event.h provides a generic event loop implementation, based on Linux
15       epoll(7).
16
17       See sd_event_new(3), sd_event_run(3), sd_event_add_io(3),
18       sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3),
19       sd_event_add_inotify(3), sd_event_add_defer(3),
20       sd_event_source_unref(3), sd_event_source_set_priority(3),
21       sd_event_source_set_enabled(3), sd_event_source_set_userdata(3),
22       sd_event_source_get_event(3), sd_event_source_get_pending(3),
23       sd_event_source_set_description(3), sd_event_source_set_prepare(3),
24       sd_event_wait(3), sd_event_get_fd(3), sd_event_set_watchdog(3),
25       sd_event_exit(3), sd_event_now(3) for more information about the
26       functions available.
27
28       The event loop design is targeted on running a separate instance of the
29       event loop in each thread; it has no concept of distributing events
30       from a single event loop instance onto multiple worker threads.
31       Dispatching events is strictly ordered and subject to configurable
32       priorities. In each event loop iteration a single event source is
33       dispatched. Each time an event source is dispatched the kernel is
34       polled for new events, before the next event source is dispatched. The
35       event loop is designed to honor priorities and provide fairness within
36       each priority. It is not designed to provide optimal throughput, as
37       this contradicts these goals due the limitations of the underlying
38       epoll(7) primitives.
39
40       The event loop implementation provides the following features:
41
42        1. I/O event sources, based on epoll(7)'s file descriptor watching,
43           including edge triggered events (EPOLLET). See sd_event_add_io(3).
44
45        2. Timer event sources, based on timerfd_create(2), supporting the
46           CLOCK_MONOTONIC, CLOCK_REALTIME, CLOCK_BOOTIME clocks, as well as
47           the CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM clocks that can
48           resume the system from suspend. When creating timer events a
49           required accuracy parameter may be specified which allows
50           coalescing of timer events to minimize power consumption. See
51           sd_event_add_time(3).
52
53        3. UNIX process signal events, based on signalfd(2), including full
54           support for real-time signals, and queued parameters. See
55           sd_event_add_signal(3).
56
57        4. Child process state change events, based on waitid(2). See
58           sd_event_add_child(3).
59
60        5. Static event sources, of three types: defer, post and exit, for
61           invoking calls in each event loop, after other event sources or at
62           event loop termination. See sd_event_add_defer(3).
63
64        6. Event sources may be assigned a 64bit priority value, that controls
65           the order in which event sources are dispatched if multiple are
66           pending simultaneously. See sd_event_source_set_priority(3).
67
68        7. The event loop may automatically send watchdog notification
69           messages to the service manager. See sd_event_set_watchdog(3).
70
71        8. The event loop may be integrated into foreign event loops, such as
72           the GLib one. See sd_event_get_fd(3) for an example.
73

NOTES

75       These APIs are implemented as a shared library, which can be compiled
76       and linked to with the libsystemd pkg-config(1) file.
77

NAME

SYNOPSIS

DESCRIPTION

NOTES

SEE ALSO