sd-event(3)

1SD-EVENT(3)                        sd-event                        SD-EVENT(3)
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NAME

6       sd-event - A generic event loop implementation
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SYNOPSIS

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

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

77       Functions described here are available as a shared library, which can
78       be compiled against and linked to with the libsystemd pkg-config(1)
79       file.
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81       The code described here uses getenv(3), which is declared to be not
82       multi-thread-safe. This means that the code calling the functions
83       described here must not call setenv(3) from a parallel thread. It is
84       recommended to only do calls to setenv() from an early phase of the
85       program when no other threads have been started.
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NAME

SYNOPSIS

DESCRIPTION

NOTES

SEE ALSO