x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_EVENT_ADD_TIME(3) sd_event_add_time SD_EVENT_ADD_TIME(3)
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
(<mu>s), 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 <mu>s specifying
how much the timer event may be delayed. Use 0 to select the default
accuracy (250ms). Use 1<mu>s for maximum accuracy. Consider specifying
60000000<mu>s (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 <mu>s. 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 <mu>s.
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 <mu>s.
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 <mu>s.
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).
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.
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)
systemd 254 SD_EVENT_ADD_TIME(3)
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