Provided by: libsystemd-dev_255.4-1ubuntu8.5_amd64 bug

NAME

       sd_event_add_time, sd_event_add_time_relative, sd_event_source_get_time, sd_event_source_set_time,
       sd_event_source_set_time_relative, sd_event_source_get_time_accuracy, sd_event_source_set_time_accuracy,
       sd_event_source_get_time_clock, sd_event_time_handler_t - Add a timer event source to an event loop

SYNOPSIS

       #include <systemd/sd-event.h>

       typedef struct sd_event_source sd_event_source;

       typedef int (*sd_event_time_handler_t)(sd_event_source *s, uint64_t usec, void *userdata);

       int sd_event_add_time(sd_event *event, sd_event_source **source, clockid_t clock, uint64_t usec,
                             uint64_t accuracy, sd_event_time_handler_t handler, void *userdata);

       int sd_event_add_time_relative(sd_event *event, sd_event_source **source, clockid_t clock, uint64_t usec,
                                      uint64_t accuracy, sd_event_time_handler_t handler, void *userdata);

       int sd_event_source_get_time(sd_event_source *source, uint64_t *usec);

       int sd_event_source_set_time(sd_event_source *source, uint64_t usec);

       int sd_event_source_set_time_relative(sd_event_source *source, uint64_t usec);

       int sd_event_source_get_time_accuracy(sd_event_source *source, uint64_t *usec);

       int sd_event_source_set_time_accuracy(sd_event_source *source, uint64_t usec);

       int sd_event_source_get_time_clock(sd_event_source *source, clockid_t *clock);

DESCRIPTION

       sd_event_add_time() adds a new timer event source to an event loop. The event loop object is specified in
       the event parameter, the event source object is returned in the source parameter. The clock parameter
       takes a clock identifier, one of CLOCK_REALTIME, CLOCK_MONOTONIC, CLOCK_BOOTTIME, CLOCK_REALTIME_ALARM,
       or CLOCK_BOOTTIME_ALARM. See timerfd_create(2) for details regarding the various types of clocks. The
       usec parameter specifies the earliest time, in microseconds (μs), relative to the clock's epoch, when the
       timer shall be triggered. If a time already in the past is specified (including 0), this timer source
       "fires" immediately and is ready to be dispatched. If the parameter is specified as UINT64_MAX the timer
       event will never elapse, which may be used as an alternative to explicitly disabling a timer event source
       with sd_event_source_set_enabled(3). The accuracy parameter specifies an additional accuracy value in μs
       specifying how much the timer event may be delayed. Use 0 to select the default accuracy (250ms). Use 1μs
       for maximum accuracy. Consider specifying 60000000μs (1min) or larger for long-running events that may be
       delayed substantially. Picking higher accuracy values allows the system to coalesce timer events more
       aggressively, improving power efficiency.

       The handler is a function to call when the timer elapses or NULL. The userdata pointer will be passed to
       the handler function, and may be chosen freely by the caller. The configured trigger time is also passed
       to the handler, even if the call actually happens slightly later, subject to the specified accuracy
       value, the kernel timer slack (see prctl(2)), and additional scheduling latencies. To query the actual
       time the handler was called use sd_event_now(3). The handler may return negative to signal an error (see
       below), other return values are ignored. If handler is NULL, a default handler that calls
       sd_event_exit(3) will be used.

       By default, the timer will elapse once (SD_EVENT_ONESHOT), but this may be changed with
       sd_event_source_set_enabled(3). If the handler function returns a negative error code, it will either be
       disabled after the invocation, even if the SD_EVENT_ON mode was requested before, or it will cause the
       loop to terminate, see sd_event_source_set_exit_on_failure(3). Note that a timer event set to SD_EVENT_ON
       will fire continuously unless its configured time is updated using sd_event_source_set_time().

       sd_event_add_time_relative() is like sd_event_add_time(), but takes a relative time specification. It's
       relative to the current time of the event loop iteration, as returned by sd_event_now(3).

       To destroy an event source object use sd_event_source_unref(3), but note that the event source is only
       removed from the event loop when all references to the event source are dropped. To make sure an event
       source does not fire anymore, even if it is still referenced, disable the event source using
       sd_event_source_set_enabled(3) with SD_EVENT_OFF.

       If the second parameter of sd_event_add_time() is NULL no reference to the event source object is
       returned. In this case the event source is considered "floating", and will be destroyed implicitly when
       the event loop itself is destroyed.

       If the handler parameter to sd_event_add_time() is NULL, and the event source fires, this will be
       considered a request to exit the event loop. In this case, the userdata parameter, cast to an integer, is
       passed as the exit code parameter to sd_event_exit(3).

       Use CLOCK_BOOTTIME_ALARM and CLOCK_REALTIME_ALARM to define event sources that may wake up the system
       from suspend.

       In order to set up relative timers (that is, relative to the current time), retrieve the current time via
       sd_event_now(3), add the desired timespan to it, and use the result as the usec parameter to
       sd_event_add_time().

       In order to set up repetitive timers (that is, timers that are triggered in regular intervals), set up
       the timer normally, for the first invocation. Each time the event handler is invoked, update the timer's
       trigger time with sd_event_source_set_time(3) for the next timer iteration, and reenable the timer using
       sd_event_source_set_enabled(). To calculate the next point in time to pass to sd_event_source_set_time(),
       either use as base the usec parameter passed to the timer callback, or the timestamp returned by
       sd_event_now(). In the former case timer events will be regular, while in the latter case the scheduling
       latency will keep accumulating on the timer.

       sd_event_source_get_time() retrieves the configured time value of an event source created previously with
       sd_event_add_time() or sd_event_add_time_relative(). It takes the event source object and a pointer to a
       variable to store the time in, relative to the selected clock's epoch, in μs. The returned value is
       relative to the epoch, even if the event source was created with a relative time via
       sd_event_add_time_relative().

       sd_event_source_set_time() changes the time of an event source created previously with
       sd_event_add_time() or sd_event_add_time_relative(). It takes the event source object and a time relative
       to the selected clock's epoch, in μs.

       sd_event_source_set_time_relative() is similar to sd_event_source_set_time(), but takes a time relative
       to the current time of the event loop iteration, as returned by sd_event_now().

       sd_event_source_get_time_accuracy() retrieves the configured accuracy value of an event source created
       previously with sd_event_add_time(). It takes the event source object and a pointer to a variable to
       store the accuracy in. The accuracy is specified in μs.

       sd_event_source_set_time_accuracy() changes the configured accuracy of a timer event source created
       previously with sd_event_add_time(). It takes the event source object and accuracy, in μs.

       sd_event_source_get_time_clock() retrieves the configured clock of an event source created previously
       with sd_event_add_time(). It takes the event source object and a pointer to a variable to store the clock
       identifier in.

RETURN VALUE

       On success, these functions return 0 or a positive integer. On failure, they return a negative
       errno-style error code.

   Errors
       Returned values may indicate the following problems:

       -ENOMEM
           Not enough memory to allocate an object.

       -EINVAL
           An invalid argument has been passed.

       -ESTALE
           The event loop is already terminated.

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

       -EOPNOTSUPP
           The selected clock is not supported by the event loop implementation.

       -EDOM
           The passed event source is not a timer event source.

       -EOVERFLOW
           The passed relative time is outside of the allowed range for time values (i.e. the specified value
           added to the current time is outside the 64 bit unsigned integer range).

           Added in version 247.

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_add_time(), sd_event_source_get_time(), sd_event_source_set_time(),
       sd_event_source_get_time_accuracy(), sd_event_source_set_time_accuracy(), and
       sd_event_source_get_time_clock() were added in version 213.

       sd_event_time_handler_t() was added in version 217.

       sd_event_add_time_relative() and sd_event_source_set_time_relative() were added in version 247.

SEE ALSO

       systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3), sd_event_add_io(3), sd_event_add_signal(3),
       sd_event_add_child(3), sd_event_add_inotify(3), sd_event_add_defer(3), sd_event_source_set_enabled(3),
       sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_set_description(3),
       sd_event_source_set_floating(3), clock_gettime(2), timerfd_create(2), prctl(2)