sd_event_source_set_ratelimit(3) — Linux manual page



NAME         top

       sd_event_source_set_ratelimit, sd_event_source_get_ratelimit,
       sd_event_source_set_ratelimit_expire_callback - 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,

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.

       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.

       Returned errors may indicate the following problems:

           source is not a valid pointer to an sd_event_source object.

           The event loop has been created in a different process.

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

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

NOTES         top

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

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

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2022-12-17.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2022-12-16.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to

systemd 252                             SD_EVENT_SOURCE_SET_RATELIMIT(3)

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