sd_event

Name

sd_event_new, sd_event_default, sd_event_ref, sd_event_unref — Acquire and release an event loop object

Synopsis

#include <systemd/sd-bus.h>

int sd_event_new( sd_bus **event);

int sd_event_default( sd_bus **event);

sd_bus *sd_event_ref( sd_bus *event);

sd_bus *sd_event_unref( sd_bus *event);

Description¶

sd_event_new() allocates a new event loop object. The event loop object is returned in the event parameter. After use, drop the returned reference with sd_event_unref(). When the last reference is dropped, the event loop is freed.

sd_event_default() acquires a reference to the default event loop object of the calling thread, possibly allocating a new object if no default event loop object has been allocated yet for the thread. After use, drop the returned reference with sd_event_unref(). When the last reference is dropped, the event loop is freed. If this function is called while the object returned from a previous call from the same thread is still referenced, the same object is returned again, but the reference is increased by one. It is recommended to use this call instead of sd_event_new() in order to share event loop objects between various components that are dispatched in the same thread. All threads either have exactly zero or one default event loop associated, but never more.

sd_event_ref() increases the reference counter of the specified event loop object by one.

sd_event_unref() decreases the reference counter of the specified event loop object by one. If the counter hits zero, the event loop object is freed. Note that it is freed regardless of whether it is the default event loop object for a thread or not. This means that allocating an event loop with sd_event_default(), then releasing it, and then acquiring a new one with sd_event_default() will result in two distinct objects. Note that, in order to free an event loop object, all remaining event sources of the event loop also need to be freed as they each keep a reference to it.

Return Value¶

On success, sd_event_new() and sd_event_default() return 0 or a positive integer. On failure, they return a negative errno-style error code. sd_event_ref() always returns a pointer to the event loop object passed in. sd_event_unref() always returns NULL.

Errors¶

Returned errors may indicate the following problems:

-ENOMEM¶: Not enough memory to allocate object
-EMFILE¶: The maximum number of event loops has been allocated.

Notes¶

sd_event_new() and the other functions described here are available as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.