|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | SEE ALSO | COLOPHON |
SD_EVENT_ADD_TIME(3) sd_event_add_time SD_EVENT_ADD_TIME(3)
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, sd_event_source_get_time_clock,
sd_event_time_handler_t - Add a timer event source to an event loop
#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_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_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);
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 parameter
shall reference a function to call when the timer elapses. The
handler function will be passed the userdata pointer, which may be
chosen freely by the caller. The handler is also passed the
configured trigger time, even if it is actually called 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).
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 be disabled after the
invocation, even if the SD_EVENT_ON mode was requested before. 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().
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 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 used for
the exit code passed 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(). 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.
sd_event_source_set_time() changes the time of an event source
created previously with sd_event_add_time(). It takes the event
source object and a time relative to the selected clock's epoch, in
µs.
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.
On success, these functions return 0 or a positive integer. On
failure, they return a negative errno-style error code.
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.
-EOPNOTSUPP
The selected clock is not supported by the event loop
implementation.
-EDOM
The passed event source is not a timer event source.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
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_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), clock_gettime(2),
timerfd_create(2), prctl(2)
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
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⟨https://github.com/systemd/systemd.git⟩ on 2017-07-05. If you dis‐
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you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
systemd 234 SD_EVENT_ADD_TIME(3)
Pages that refer to this page: sd-event(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_io(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_new(3), sd_event_now(3), sd_event_run(3), sd_event_set_watchdog(3), sd_event_source_get_event(3), sd_event_source_get_pending(3), sd_event_source_set_description(3), sd_event_source_set_enabled(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)