sd_event_add_time(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. The handler parameter shall
68       reference a function to call when the timer elapses. The handler
69       function will be passed the userdata pointer, which may be chosen
70       freely by the caller. The handler is also passed the configured trigger
71       time, even if it is actually called slightly later, subject to the
72       specified accuracy value, the kernel timer slack (see prctl(2)), and
73       additional scheduling latencies. To query the actual time the handler
74       was called use sd_event_now(3).
75
76       By default, the timer will elapse once (SD_EVENT_ONESHOT), but this may
77       be changed with sd_event_source_set_enabled(3). If the handler function
78       returns a negative error code, it will be disabled after the
79       invocation, even if the SD_EVENT_ON mode was requested before. Note
80       that a timer event set to SD_EVENT_ON will fire continuously unless its
81       configured time is updated using sd_event_source_set_time().
82
83       sd_event_add_time_relative() is like sd_event_add_time(), but takes a
84       relative time specification. It's relative to the current time of the
85       event loop iteration, as returned by sd_event_now(3).
86
87       To destroy an event source object use sd_event_source_unref(3), but
88       note that the event source is only removed from the event loop when all
89       references to the event source are dropped. To make sure an event
90       source does not fire anymore, even if it is still referenced, disable
91       the event source using sd_event_source_set_enabled(3) with
92       SD_EVENT_OFF.
93
94       If the second parameter of sd_event_add_time() is NULL no reference to
95       the event source object is returned. In this case the event source is
96       considered "floating", and will be destroyed implicitly when the event
97       loop itself is destroyed.
98
99       If the handler parameter to sd_event_add_time() is NULL, and the event
100       source fires, this will be considered a request to exit the event loop.
101       In this case, the userdata parameter, cast to an integer, is passed as
102       the exit code parameter to sd_event_exit(3).
103
104       Use CLOCK_BOOTTIME_ALARM and CLOCK_REALTIME_ALARM to define event
105       sources that may wake up the system from suspend.
106
107       In order to set up relative timers (that is, relative to the current
108       time), retrieve the current time via sd_event_now(3), add the desired
109       timespan to it, and use the result as the usec parameter to
110       sd_event_add_time().
111
112       In order to set up repetitive timers (that is, timers that are
113       triggered in regular intervals), set up the timer normally, for the
114       first invocation. Each time the event handler is invoked, update the
115       timer's trigger time with sd_event_source_set_time(3) for the next
116       timer iteration, and reenable the timer using
117       sd_event_source_set_enabled(). To calculate the next point in time to
118       pass to sd_event_source_set_time(), either use as base the usec
119       parameter passed to the timer callback, or the timestamp returned by
120       sd_event_now(). In the former case timer events will be regular, while
121       in the latter case the scheduling latency will keep accumulating on the
122       timer.
123
124       sd_event_source_get_time() retrieves the configured time value of an
125       event source created previously with sd_event_add_time() or
126       sd_event_add_time_relative(). It takes the event source object and a
127       pointer to a variable to store the time in, relative to the selected
128       clock's epoch, in µs. The returned value is relative to the epoch, even
129       if the event source was created with a relative time via
130       sd_event_add_time_relative().
131
132       sd_event_source_set_time() changes the time of an event source created
133       previously with sd_event_add_time() or sd_event_add_time_relative(). It
134       takes the event source object and a time relative to the selected
135       clock's epoch, in µs.
136
137       sd_event_source_set_time_relative() is similar to
138       sd_event_source_set_time(), but takes a time relative to the current
139       time of the event loop iteration, as returned by sd_event_now().
140
141       sd_event_source_get_time_accuracy() retrieves the configured accuracy
142       value of an event source created previously with sd_event_add_time().
143       It takes the event source object and a pointer to a variable to store
144       the accuracy in. The accuracy is specified in µs.
145
146       sd_event_source_set_time_accuracy() changes the configured accuracy of
147       a timer event source created previously with sd_event_add_time(). It
148       takes the event source object and accuracy, in µs.
149
150       sd_event_source_get_time_clock() retrieves the configured clock of an
151       event source created previously with sd_event_add_time(). It takes the
152       event source object and a pointer to a variable to store the clock
153       identifier in.
154

RETURN VALUE

156       On success, these functions return 0 or a positive integer. On failure,
157       they return a negative errno-style error code.
158
159   Errors
160       Returned values may indicate the following problems:
161
162       -ENOMEM
163           Not enough memory to allocate an object.
164
165       -EINVAL
166           An invalid argument has been passed.
167
168       -ESTALE
169           The event loop is already terminated.
170
171       -ECHILD
172           The event loop has been created in a different process.
173
174       -EOPNOTSUPP
175           The selected clock is not supported by the event loop
176           implementation.
177
178       -EDOM
179           The passed event source is not a timer event source.
180
181       -EOVERFLOW
182           The passed relative time is outside of the allowed range for time
183           values (i.e. the specified value added to the current time is
184           outside the 64 bit unsigned integer range).
185

NOTES

187       These APIs are implemented as a shared library, which can be compiled
188       and linked to with the libsystemd pkg-config(1) file.
189

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

SEE ALSO