NAME

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

SYNOPSIS

       #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);

DESCRIPTION

       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.

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

RETURN VALUE

       On success, sd_event_source_set_ratelimit() 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.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           source is not a valid pointer to an sd_event_source object.

       -ECHILD
           The event loop has been created in a different process.

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

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

NOTES

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

SEE ALSO

       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)

systemd 249                                                                     SD_EVENT_SOURCE_SET_RATELIMIT(3)