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_source_get_time, sd_event_source_set_time,
7       sd_event_source_get_time_accuracy, sd_event_source_set_time_accuracy,
8       sd_event_source_get_time_clock, sd_event_time_handler_t - Add a timer
9       event source to an event loop
10

SYNOPSIS

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

DESCRIPTION

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

RETURN VALUE

133       On success, these functions return 0 or a positive integer. On failure,
134       they return a negative errno-style error code.
135

ERRORS

137       Returned values may indicate the following problems:
138
139       -ENOMEM
140           Not enough memory to allocate an object.
141
142       -EINVAL
143           An invalid argument has been passed.
144
145       -ESTALE
146           The event loop is already terminated.
147
148       -ECHILD
149           The event loop has been created in a different process.
150
151       -EOPNOTSUPP
152           The selected clock is not supported by the event loop
153           implementation.
154
155       -EDOM
156           The passed event source is not a timer event source.
157

NOTES

159       These APIs are implemented as a shared library, which can be compiled
160       and linked to with the libsystemd pkg-config(1) file.
161

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

NOTES

SEE ALSO