NAME

       sd_event_source_set_enabled, sd_event_source_get_enabled, SD_EVENT_ON, SD_EVENT_OFF, SD_EVENT_ONESHOT -
       Enable or disable event sources

SYNOPSIS

       #include <systemd/sd-event.h>

       enum {
               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);

DESCRIPTION

       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.

RETURN VALUE

       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.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           source is not a valid pointer to an sd_event_source object.

       -ENOMEM
           Not enough memory.

       -ECHILD
           The event loop has been created in a different process, library or module instance.

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.

       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.

HISTORY

       sd_event_source_set_enabled() and sd_event_source_get_enabled() were added in version 229.

SEE ALSO

       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)