sd_event_set_watchdog, sd_event_get_watchdog — Enable event loop watchdog support
#include <systemd/sd-event.h>
int sd_event_set_watchdog( | sd_event *event, |
int b); |
int sd_event_get_watchdog( | sd_event *event); |
sd_event_set_watchdog() may be used to
enable or disable automatic watchdog notification support in the
event loop object specified in the event
parameter. Specifically, depending on the b
boolean argument this will make sure the event loop wakes up in
regular intervals and sends watchdog notification messages to the
service manager, if this was requested by the service
manager. Watchdog support is determined with
sd_watchdog_enabled(3),
and watchdog messages are sent with
sd_notify(3). See
the WatchdogSec= setting in
systemd.service(5)
for details on how to enable watchdog support for a service and
the protocol used. The wake-up interval is chosen as half the
watchdog timeout declared by the service manager via the
$WATCHDOG_USEC environment variable. If the
service manager did not request watchdog notifications, or if the
process was not invoked by the service manager this call with a
true b parameter executes no
operation. Passing a false b parameter will
disable the automatic sending of watchdog notification messages if
it was enabled before. Newly allocated event loop objects have
this feature disabled.
The first watchdog notification message is sent immediately
when sd_event_set_watchdog() is invoked with
a true b parameter.
The watchdog logic is designed to allow the service manager to automatically detect services that ceased processing of incoming events, and thus appear "hung". Watchdog notifications are sent out only at the beginning of each event loop iteration. If an event source dispatch function blocks for an excessively long time and does not return execution to the event loop quickly, this might hence cause the notification message to be delayed, and possibly result in abnormal program termination, as configured in the service unit file.
sd_event_get_watchdog() may be used to
determine whether watchdog support was previously requested by a
call to sd_event_set_watchdog() with a true
b parameter and successfully
enabled.
On success, sd_event_set_watchdog() and
sd_event_get_watchdog() return a non-zero positive integer if the service manager
requested watchdog support and watchdog support was successfully enabled. They return zero if the service
manager did not request watchdog support, or if watchdog support was explicitly disabled with a false
b parameter. 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.