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
#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); |
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.
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:
-EINVAL¶source is not a valid pointer to an
sd_event_source object.
-ECHILD¶The event loop has been created in a different process, library or module instance.
-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.
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.
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.