Ubuntu Manpage: sd_event_source_set_ratelimit, sd_event_source_get

Provided by: libsystemd-dev_256.5-2ubuntu3.1_amd64

NAME

       sd_event_source_set_ratelimit, sd_event_source_get_ratelimit,
       sd_event_source_is_ratelimited, sd_event_source_set_ratelimit_expire_callback,
       sd_event_source_leave_ratelimit - 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);

       int sd_event_source_set_ratelimit_expire_callback(sd_event_source *source,
                                                         sd_event_handler_tcallback);

       int sd_event_source_leave_ratelimit(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.

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

       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.

   Errors
       Returned errors may indicate the following problems:

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

           Added in version 248.

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

           Added in version 248.

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

           Added in version 248.

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

           Added in version 248.

NOTES

       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 started.

HISTORY