sd_event_source_set_ratelimit(3) — Linux manual page


SD_EVEN...ATELIMIT(3) sd_event_source_set_ratelimitSD_EVEN...ATELIMIT(3)

NAME         top

       sd_event_source_set_ratelimit, sd_event_source_get_ratelimit,
       sd_event_source_leave_ratelimit - Configure rate limiting on
       event sources

SYNOPSIS         top

       #include <systemd/sd-event.h>

       int sd_event_source_set_ratelimit(sd_event_source *source,
                                         uint64_t interval_usec,
                                         unsigned burst);

       int sd_event_source_get_ratelimit(sd_event_source *source,
                                         uint64_t* ret_interval_usec,
                                         unsigned* ret_burst);

       int sd_event_source_is_ratelimited(sd_event_source *source);

                                                         sd_event_source_set_ratelimit_expire_callback(sd_event_source *source,

       int sd_event_source_leave_ratelimit(sd_event_source *source);

DESCRIPTION         top

       sd_event_source_set_ratelimit() may be used to enforce rate
       limiting on an event source. When used an event source will be
       temporarily turned off when it fires more often then a specified
       burst number within a specified time interval. This is useful as
       simple mechanism to avoid event source starvation if high
       priority event sources fire very frequently.

       Pass the event source to operate on as first argument, a time
       interval in microseconds as second argument and a maximum
       dispatch limit ("burst") as third parameter. Whenever the event
       source is dispatched more often than the specified burst within
       the specified interval it is placed in a mode similar to being
       disabled with sd_event_source_set_enabled(3) and the SD_EVENT_OFF
       parameter. However it is disabled only temporarily – once the
       specified interval is over regular operation resumes. It is again
       disabled temporarily once the specified rate limiting is hit the
       next time. If either the interval or the burst value are
       specified as zero, rate limiting is turned off. By default event
       sources do not have rate limiting enabled. Note that rate
       limiting and disabling via sd_event_source_set_enabled() are
       independent of each other, and an event source will only effect
       event loop wake-ups and is dispatched while it both is enabled
       and rate limiting is not in effect.

       sd_event_source_get_ratelimit() may be used to query the current
       rate limiting parameters set on the event source object source.
       The previously set interval and burst vales are returned in the
       second and third argument.

       sd_event_source_is_ratelimited() may be used to query whether the
       event source is currently affected by rate limiting, i.e. it has
       recently hit the rate limit and is currently temporarily disabled
       due to that.

       sd_event_source_set_ratelimit_expire_callback() may be used to
       set a callback function that is invoked every time the event
       source leaves rate limited state. Note that function is called in
       the same event loop iteration in which state transition occurred.

       sd_event_source_leave_ratelimit() may be used to immediately
       reenable an event source that was temporarily disabled due to
       rate limiting. This will reset the ratelimit counters for the
       current time interval.

       Rate limiting is currently implemented for I/O, timer, signal,
       defer and inotify event sources.

RETURN VALUE         top

       On success, sd_event_source_set_ratelimit(),
       sd_event_source_set_ratelimit_expire_callback and
       sd_event_source_get_ratelimit() return a non-negative integer. On
       failure, they return a negative errno-style error code.
       sd_event_source_is_ratelimited() returns zero if rate limiting is
       currently not in effect and greater than zero if it is in effect;
       it returns a negative errno-style error code on failure.
       sd_event_source_leave_ratelimit() returns zero if rate limiting
       wasn't in effect on the specified event source, and positive if
       it was and rate limiting is now turned off again; it returns a
       negative errno-style error code on failure.

       Returned errors may indicate the following problems:

           source is not a valid pointer to an sd_event_source object.

           Added in version 248.

           The event loop has been created in a different process,
           library or module instance.

           Added in version 248.

           It was attempted to use the rate limiting feature on an event
           source type that does not support rate limiting.

           Added in version 248.

           sd_event_source_get_ratelimit() was called on an event source
           that doesn't have rate limiting configured.

           Added in version 248.

NOTES         top

       Functions described here are available as a shared library, which
       can be compiled against and linked to with the
       libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be
       not multi-thread-safe. This means that the code calling the
       functions described here must not call setenv(3) from a parallel
       thread. It is recommended to only do calls to setenv() from an
       early phase of the program when no other threads have been

HISTORY         top

       sd_event_source_set_ratelimit(), sd_event_source_get_ratelimit(),
       and sd_event_source_is_ratelimited() were added in version 248.

       sd_event_source_set_ratelimit_expire_callback() was added in
       version 250.

       sd_event_source_leave_ratelimit() was added in version 254.

SEE ALSO         top

       sd-event(3), sd_event_add_io(3), sd_event_add_time(3),
       sd_event_add_signal(3), sd_event_add_inotify(3),
       sd_event_add_defer(3), sd_event_source_set_enabled(3)

COLOPHON         top

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       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
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systemd 255                                        SD_EVEN...ATELIMIT(3)

Pages that refer to this page: sd-event(3)sd_event_source_set_enabled(3)systemd.directives(7)systemd.index(7)