sd_event_source_set_time_accuracy(3)

1SD_EVENT_ADD_TIME(3)           sd_event_add_time          SD_EVENT_ADD_TIME(3)
2
3
4

NAME

6       sd_event_add_time, sd_event_add_time_relative,
7       sd_event_source_get_time, sd_event_source_set_time,
8       sd_event_source_set_time_relative, sd_event_source_get_time_accuracy,
9       sd_event_source_set_time_accuracy, sd_event_source_get_time_clock,
10       sd_event_time_handler_t - Add a timer event source to an event loop
11

SYNOPSIS

13       #include <systemd/sd-event.h>
14
15       typedef struct sd_event_source sd_event_source;
16
17       typedef int (*sd_event_time_handler_t)(sd_event_source *s,
18                                              uint64_t usec, void *userdata);
19
20       int sd_event_add_time(sd_event *event, sd_event_source **source,
21                             clockid_t clock, uint64_t usec,
22                             uint64_t accuracy,
23                             sd_event_time_handler_t handler, void *userdata);
24
25       int sd_event_add_time_relative(sd_event *event,
26                                      sd_event_source **source,
27                                      clockid_t clock, uint64_t usec,
28                                      uint64_t accuracy,
29                                      sd_event_time_handler_t handler,
30                                      void *userdata);
31
32       int sd_event_source_get_time(sd_event_source *source, uint64_t *usec);
33
34       int sd_event_source_set_time(sd_event_source *source, uint64_t usec);
35
36       int sd_event_source_set_time_relative(sd_event_source *source,
37                                             uint64_t usec);
38
39       int sd_event_source_get_time_accuracy(sd_event_source *source,
40                                             uint64_t *usec);
41
42       int sd_event_source_set_time_accuracy(sd_event_source *source,
43                                             uint64_t usec);
44
45       int sd_event_source_get_time_clock(sd_event_source *source,
46                                          clockid_t *clock);
47

DESCRIPTION

49       sd_event_add_time() adds a new timer event source to an event loop. The
50       event loop object is specified in the event parameter, the event source
51       object is returned in the source parameter. The clock parameter takes a
52       clock identifier, one of CLOCK_REALTIME, CLOCK_MONOTONIC,
53       CLOCK_BOOTTIME, CLOCK_REALTIME_ALARM, or CLOCK_BOOTTIME_ALARM. See
54       timerfd_create(2) for details regarding the various types of clocks.
55       The usec parameter specifies the earliest time, in microseconds (µs),
56       relative to the clock's epoch, when the timer shall be triggered. If a
57       time already in the past is specified (including 0), this timer source
58       "fires" immediately and is ready to be dispatched. If the parameter is
59       specified as UINT64_MAX the timer event will never elapse, which may be
60       used as an alternative to explicitly disabling a timer event source
61       with sd_event_source_set_enabled(3). The accuracy parameter specifies
62       an additional accuracy value in µs specifying how much the timer event
63       may be delayed. Use 0 to select the default accuracy (250ms). Use 1µs
64       for maximum accuracy. Consider specifying 60000000µs (1min) or larger
65       for long-running events that may be delayed substantially. Picking
66       higher accuracy values allows the system to coalesce timer events more
67       aggressively, improving power efficiency.
68
69       The handler is a function to call when the timer elapses or NULL. The
70       userdata pointer will be passed to the handler function, and may be
71       chosen freely by the caller. The configured trigger time is also passed
72       to the handler, even if the call actually happens slightly later,
73       subject to the specified accuracy value, the kernel timer slack (see
74       prctl(2)), and additional scheduling latencies. To query the actual
75       time the handler was called use sd_event_now(3). The handler may return
76       negative to signal an error (see below), other return values are
77       ignored. If handler is NULL, a default handler that calls
78       sd_event_exit(3) will be used.
79
80       By default, the timer will elapse once (SD_EVENT_ONESHOT), but this may
81       be changed with sd_event_source_set_enabled(3). If the handler function
82       returns a negative error code, it will either be disabled after the
83       invocation, even if the SD_EVENT_ON mode was requested before, or it
84       will cause the loop to terminate, see
85       sd_event_source_set_exit_on_failure(3). Note that a timer event set to
86       SD_EVENT_ON will fire continuously unless its configured time is
87       updated using sd_event_source_set_time().
88
89       sd_event_add_time_relative() is like sd_event_add_time(), but takes a
90       relative time specification. It's relative to the current time of the
91       event loop iteration, as returned by sd_event_now(3).
92
93       To destroy an event source object use sd_event_source_unref(3), but
94       note that the event source is only removed from the event loop when all
95       references to the event source are dropped. To make sure an event
96       source does not fire anymore, even if it is still referenced, disable
97       the event source using sd_event_source_set_enabled(3) with
98       SD_EVENT_OFF.
99
100       If the second parameter of sd_event_add_time() is NULL no reference to
101       the event source object is returned. In this case the event source is
102       considered "floating", and will be destroyed implicitly when the event
103       loop itself is destroyed.
104
105       If the handler parameter to sd_event_add_time() is NULL, and the event
106       source fires, this will be considered a request to exit the event loop.
107       In this case, the userdata parameter, cast to an integer, is passed as
108       the exit code parameter to sd_event_exit(3).
109
110       Use CLOCK_BOOTTIME_ALARM and CLOCK_REALTIME_ALARM to define event
111       sources that may wake up the system from suspend.
112
113       In order to set up relative timers (that is, relative to the current
114       time), retrieve the current time via sd_event_now(3), add the desired
115       timespan to it, and use the result as the usec parameter to
116       sd_event_add_time().
117
118       In order to set up repetitive timers (that is, timers that are
119       triggered in regular intervals), set up the timer normally, for the
120       first invocation. Each time the event handler is invoked, update the
121       timer's trigger time with sd_event_source_set_time(3) for the next
122       timer iteration, and reenable the timer using
123       sd_event_source_set_enabled(). To calculate the next point in time to
124       pass to sd_event_source_set_time(), either use as base the usec
125       parameter passed to the timer callback, or the timestamp returned by
126       sd_event_now(). In the former case timer events will be regular, while
127       in the latter case the scheduling latency will keep accumulating on the
128       timer.
129
130       sd_event_source_get_time() retrieves the configured time value of an
131       event source created previously with sd_event_add_time() or
132       sd_event_add_time_relative(). It takes the event source object and a
133       pointer to a variable to store the time in, relative to the selected
134       clock's epoch, in µs. The returned value is relative to the epoch, even
135       if the event source was created with a relative time via
136       sd_event_add_time_relative().
137
138       sd_event_source_set_time() changes the time of an event source created
139       previously with sd_event_add_time() or sd_event_add_time_relative(). It
140       takes the event source object and a time relative to the selected
141       clock's epoch, in µs.
142
143       sd_event_source_set_time_relative() is similar to
144       sd_event_source_set_time(), but takes a time relative to the current
145       time of the event loop iteration, as returned by sd_event_now().
146
147       sd_event_source_get_time_accuracy() retrieves the configured accuracy
148       value of an event source created previously with sd_event_add_time().
149       It takes the event source object and a pointer to a variable to store
150       the accuracy in. The accuracy is specified in µs.
151
152       sd_event_source_set_time_accuracy() changes the configured accuracy of
153       a timer event source created previously with sd_event_add_time(). It
154       takes the event source object and accuracy, in µs.
155
156       sd_event_source_get_time_clock() retrieves the configured clock of an
157       event source created previously with sd_event_add_time(). It takes the
158       event source object and a pointer to a variable to store the clock
159       identifier in.
160

RETURN VALUE

162       On success, these functions return 0 or a positive integer. On failure,
163       they return a negative errno-style error code.
164
165   Errors
166       Returned values may indicate the following problems:
167
168       -ENOMEM
169           Not enough memory to allocate an object.
170
171       -EINVAL
172           An invalid argument has been passed.
173
174       -ESTALE
175           The event loop is already terminated.
176
177       -ECHILD
178           The event loop has been created in a different process.
179
180       -EOPNOTSUPP
181           The selected clock is not supported by the event loop
182           implementation.
183
184       -EDOM
185           The passed event source is not a timer event source.
186
187       -EOVERFLOW
188           The passed relative time is outside of the allowed range for time
189           values (i.e. the specified value added to the current time is
190           outside the 64 bit unsigned integer range).
191

NOTES

193       These APIs are implemented as a shared library, which can be compiled
194       and linked to with the libsystemd pkg-config(1) file.
195

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

SEE ALSO