plucky (3) sd_event_set_watchdog.3.gz

NAME

       sd_event_set_watchdog, sd_event_get_watchdog - Enable event loop watchdog support

SYNOPSIS

       #include <systemd/sd-event.h>

       int sd_event_set_watchdog(sd_event *event, int b);

       int sd_event_get_watchdog(sd_event *event);

DESCRIPTION

       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.

RETURN VALUE

       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.

   Errors
       Returned errors may indicate the following problems:

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

       -EINVAL
           The passed event loop object was invalid.

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_set_watchdog() and sd_event_get_watchdog() were added in version 229.

SEE ALSO

       systemd(1), sd-event(3), sd_event_new(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_watchdog_enabled(3), sd_notify(3), systemd.service(5)