sd_event_add_defer, sd_event_add_post, sd_event_add_exit, sd_event_handler_t — Add static event sources to an event loop
typedef struct sd_event_source sd_event_source;
These three functions add new static event sources to an
event loop. The event loop object is specified in the
event parameter, the event source object is
returned in the
source parameter. The event
sources are enabled statically and will "fire" when the event loop
is run and the conditions described below are met. The handler
function will be passed the
pointer, which may be chosen freely by the caller.
sd_event_add_defer() adds a new event
source that will be dispatched instantly, before the event loop
goes to sleep again and waits for new events. By default, the
handler will be called once
SD_EVENT_ONESHOT). Note that if the event
source is set to
SD_EVENT_ON the event loop
will never go to sleep again, but continuously call the handler,
possibly interleaved with other event sources.
sd_event_add_post() adds a new event
source that is run before the event loop will sleep and wait
for new events, but only after at least one other non-post event
source was dispatched. By default, the source is enabled
SD_EVENT_ON). Note that this
event source type will still allow the event loop to go to sleep
again, even if set to
SD_EVENT_ON, as long as
no other event source is ever triggered.
sd_event_add_exit() adds a new event
source that will be dispatched when the event loop is terminated
function may be used to enable the event source permanently
SD_EVENT_ON) or to make it fire just once
If the handler function returns a negative error code, it
will be disabled after the invocation, even if the
SD_EVENT_ON mode was requested before.
To destroy an event source object use
but note that the event source is only removed from the event loop
when all references to the event source are dropped. To make sure
an event source does not fire anymore, even when there's still a
reference to it kept, consider setting the event source to
If the second parameter of these functions is passed as NULL no reference to the event source object is returned. In this case the event source is considered "floating", and will be destroyed implicitly when the event loop itself is destroyed.
On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code.
Returned errors may indicate the following problems:
These APIs are implemented as a shared
library, which can be compiled and linked to with the
systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3), sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3), sd_event_source_set_enabled(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_set_description(3), sd_event_exit(3)