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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_EVEN...ATELIMIT(3) sd_event_source_set_ratelimit SD_EVEN...ATELIMIT(3)
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
was not 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 does not have rate limiting configured.
Added in version 248.
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.
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)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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