sd_event_source_set_enabled, sd_event_source_get_enabled, SD_EVENT_ON, SD_EVENT_OFF, SD_EVENT_ONESHOT — Enable or disable event sources
#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) ; |
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.
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.