# sd_event_source_set_ratelimit

## 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_t** _callback_**);**
    
           **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
           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.
    


## 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.
    


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