sd_event_run - Man Page

Run an event loop

Synopsis

#include <systemd/sd-event.h>

int sd_event_run(sd_event *event, uint64_t usec);

int sd_event_loop(sd_event *event);

sd_event_run() may be used to run a single iteration of the event loop specified in the event parameter. The function waits until an event to process is available, and dispatches the registered handler for it. The usec parameter specifies the maximum time (in microseconds) to wait for an event. Use (uint64_t) -1 to specify an infinite timeout.

sd_event_loop() invokes sd_event_run() in a loop, thus implementing the actual event loop. The call returns as soon as exiting was requested using sd_event_exit(3).

The event loop object event is created with sd_event_new(3). Events sources to wait for and their handlers may be registered with sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_post(3) and sd_event_add_exit(3).

For low-level control of event loop execution, use sd_event_prepare(3), sd_event_wait(3) and sd_event_dispatch(3) which are wrapped by sd_event_run(). Along with sd_event_get_fd(3), these functions allow integration of an sd-event(3) event loop into foreign event loop implementations.

Return Value

On failure, these functions return a negative errno-style error code. sd_event_run() returns a positive, non-zero integer if an event source was dispatched, and zero when the specified timeout hit before an event source has seen any event, and hence no event source was dispatched. sd_event_loop() returns the exit code specified when invoking sd_event_exit().

Errors

Returned errors may indicate the following problems:

-EINVAL: The event parameter is invalid or NULL.
-EBUSY: The event loop object is not in the right state (see sd_event_prepare(3) for an explanation of possible states).
-ESTALE: The event loop is already terminated.
-ECHILD: The event loop has been created in a different process, library or module instance.

Other errors are possible, too.

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.

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel.

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.