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 one dispatch. For SD_EVENT_OFF, the event source source may be NULL, in which case the function does nothing. Otherwise, source must be a valid pointer to an sd_event_source object.
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. If both the source and the output parameter enabled are NULL, this function returns false. Otherwise, source must be a valid pointer to an sd_event_source object. If the output parameter enabled is not NULL, it is set to the enablement state (one of SD_EVENT_ON, SD_EVENT_OFF, SD_EVENT_ONESHOT). The function 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:
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.
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)