# sd_event_add_time

## 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 ***_ret_**);**
    
           **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 ***_ret_**);**
    
           **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 ***_ret_**);**
    


## 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.
    


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