# sd-event

## NAME



           sd-event - A generic event loop implementation
    


## SYNOPSIS



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


## DESCRIPTION



           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.
    


## NOTES



           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.
    


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