1SD_EVENT_SOURCE_SET_RATELIsMdI_Te(v3e)nt_source_set_raStDe_lEiVmEiNtT_SOURCE_SET_RATELIMIT(3)
2
3
4
6 sd_event_source_set_ratelimit, sd_event_source_get_ratelimit,
7 sd_event_source_is_ratelimited,
8 sd_event_source_set_ratelimit_expire_callback,
9 sd_event_source_leave_ratelimit - Configure rate limiting on event
10 sources
11
13 #include <systemd/sd-event.h>
14
15 int sd_event_source_set_ratelimit(sd_event_source *source,
16 uint64_t interval_usec,
17 unsigned burst);
18
19 int sd_event_source_get_ratelimit(sd_event_source *source,
20 uint64_t* ret_interval_usec,
21 unsigned* ret_burst);
22
23 int sd_event_source_is_ratelimited(sd_event_source *source);
24
25 int
26 sd_event_source_set_ratelimit_expire_callback(sd_event_source *source,
27 sd_event_handler_tcallback);
28
29 int sd_event_source_leave_ratelimit(sd_event_source *source);
30
32 sd_event_source_set_ratelimit() may be used to enforce rate limiting on
33 an event source. When used an event source will be temporarily turned
34 off when it fires more often then a specified burst number within a
35 specified time interval. This is useful as simple mechanism to avoid
36 event source starvation if high priority event sources fire very
37 frequently.
38
39 Pass the event source to operate on as first argument, a time interval
40 in microseconds as second argument and a maximum dispatch limit
41 ("burst") as third parameter. Whenever the event source is dispatched
42 more often than the specified burst within the specified interval it is
43 placed in a mode similar to being disabled with
44 sd_event_source_set_enabled(3) and the SD_EVENT_OFF parameter. However
45 it is disabled only temporarily – once the specified interval is over
46 regular operation resumes. It is again disabled temporarily once the
47 specified rate limiting is hit the next time. If either the interval or
48 the burst value are specified as zero, rate limiting is turned off. By
49 default event sources do not have rate limiting enabled. Note that rate
50 limiting and disabling via sd_event_source_set_enabled() are
51 independent of each other, and an event source will only effect event
52 loop wake-ups and is dispatched while it both is enabled and rate
53 limiting is not in effect.
54
55 sd_event_source_get_ratelimit() may be used to query the current rate
56 limiting parameters set on the event source object source. The
57 previously set interval and burst vales are returned in the second and
58 third argument.
59
60 sd_event_source_is_ratelimited() may be used to query whether the event
61 source is currently affected by rate limiting, i.e. it has recently hit
62 the rate limit and is currently temporarily disabled due to that.
63
64 sd_event_source_set_ratelimit_expire_callback() may be used to set a
65 callback function that is invoked every time the event source leaves
66 rate limited state. Note that function is called in the same event loop
67 iteration in which state transition occurred.
68
69 sd_event_source_leave_ratelimit() may be used to immediately reenable
70 an event source that was temporarily disabled due to rate limiting.
71 This will reset the ratelimit counters for the current time interval.
72
73 Rate limiting is currently implemented for I/O, timer, signal, defer
74 and inotify event sources.
75
77 On success, sd_event_source_set_ratelimit(),
78 sd_event_source_set_ratelimit_expire_callback and
79 sd_event_source_get_ratelimit() return a non-negative integer. On
80 failure, they return a negative errno-style error code.
81 sd_event_source_is_ratelimited() returns zero if rate limiting is
82 currently not in effect and greater than zero if it is in effect; it
83 returns a negative errno-style error code on failure.
84 sd_event_source_leave_ratelimit() returns zero if rate limiting wasn't
85 in effect on the specified event source, and positive if it was and
86 rate limiting is now turned off again; it returns a negative
87 errno-style error code on failure.
88
89 Errors
90 Returned errors may indicate the following problems:
91
92 -EINVAL
93 source is not a valid pointer to an sd_event_source object.
94
95 -ECHILD
96 The event loop has been created in a different process, library or
97 module instance.
98
99 -EDOM
100 It was attempted to use the rate limiting feature on an event
101 source type that does not support rate limiting.
102
103 -ENOEXEC
104 sd_event_source_get_ratelimit() was called on an event source that
105 doesn't have rate limiting configured.
106
108 Functions described here are available as a shared library, which can
109 be compiled against and linked to with the libsystemd pkg-config(1)
110 file.
111
112 The code described here uses getenv(3), which is declared to be not
113 multi-thread-safe. This means that the code calling the functions
114 described here must not call setenv(3) from a parallel thread. It is
115 recommended to only do calls to setenv() from an early phase of the
116 program when no other threads have been started.
117
119 sd-event(3), sd_event_add_io(3), sd_event_add_time(3),
120 sd_event_add_signal(3), sd_event_add_inotify(3), sd_event_add_defer(3),
121 sd_event_source_set_enabled(3)
122
123
124
125systemd 254 SD_EVENT_SOURCE_SET_RATELIMIT(3)