sd_event_source_set_enabled, sd_event_source_get_enabled, SD_EVENT_ON, SD_EVENT_OFF, SD_EVENT_ONESHOT - Enable or disable event sources
SD_EVENT_OFF = 0,
SD_EVENT_ON = 1,
SD_EVENT_ONESHOT = -1,
int sd_event_source_set_enabled(sd_event_source *source, int enabled);
int sd_event_source_get_enabled(sd_event_source *source, int *enabled);
sd_event_source_set_enabled() may be used to enable or disable the event source object specified as source. The enabled parameter takes one of SD_EVENT_ON (to enable), SD_EVENT_OFF (to disable) or SD_EVENT_ONESHOT. If invoked with SD_EVENT_ONESHOT the event source will be enabled but automatically reset to SD_EVENT_OFF after the event source was dispatched once.
Event sources that are disabled will not result in event loop wakeups and will not be dispatched, until they are enabled again.
sd_event_source_get_enabled() may be used to query whether the event source object source is currently enabled or not. It returns the enablement state (one of SD_EVENT_ON, SD_EVENT_OFF, SD_EVENT_ONESHOT) in enabled, if it is not NULL. It also returns true if the event source is not disabled.
Event source objects are enabled when they are first created with calls such as sd_event_add_io(3), sd_event_add_time(3). However, depending on the event source type they are enabled continuously (SD_EVENT_ON) or only for a single invocation of the event source handler (SD_EVENT_ONESHOT). For details see the respective manual pages.
As event source objects stay active and may be dispatched as long as there is at least one reference to them, in many cases it is a good idea to combine a call to sd_event_source_unref(3) with a prior call to sd_event_source_set_enabled() with SD_EVENT_OFF, to ensure the event source is not dispatched again until all other remaining references are dropped.
On success, sd_event_source_set_enabled() returns a non-negative integer. sd_event_source_get_enabled() returns zero if the source is disabled (SD_EVENT_OFF) and a positive integer otherwise. On failure, they return a negative errno-style error code.
Returned errors may indicate the following problems:
source is not a valid pointer to an sd_event_source object.
Not enough memory.
The event loop has been created in a different process.
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.
sd-event(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_source_unref(3), sd_event_source_set_ratelimit(3)