1<?xml version='1.0'?> 2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" 3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> 4<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> 5 6<refentry id="sd_event_source_set_ratelimit" xmlns:xi="http://www.w3.org/2001/XInclude"> 7 8 <refentryinfo> 9 <title>sd_event_source_set_ratelimit</title> 10 <productname>systemd</productname> 11 </refentryinfo> 12 13 <refmeta> 14 <refentrytitle>sd_event_source_set_ratelimit</refentrytitle> 15 <manvolnum>3</manvolnum> 16 </refmeta> 17 18 <refnamediv> 19 <refname>sd_event_source_set_ratelimit</refname> 20 <refname>sd_event_source_get_ratelimit</refname> 21 <refname>sd_event_source_is_ratelimited</refname> 22 <refname>sd_event_source_set_ratelimit_expire_callback</refname> 23 24 <refpurpose>Configure rate limiting on event sources</refpurpose> 25 </refnamediv> 26 27 <refsynopsisdiv> 28 <funcsynopsis> 29 <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> 30 31 <funcprototype> 32 <funcdef>int <function>sd_event_source_set_ratelimit</function></funcdef> 33 <paramdef>sd_event_source *<parameter>source</parameter></paramdef> 34 <paramdef>uint64_t <parameter>interval_usec</parameter></paramdef> 35 <paramdef>unsigned <parameter>burst</parameter></paramdef> 36 </funcprototype> 37 38 <funcprototype> 39 <funcdef>int <function>sd_event_source_get_ratelimit</function></funcdef> 40 <paramdef>sd_event_source *<parameter>source</parameter></paramdef> 41 <paramdef>uint64_t* <parameter>ret_interval_usec</parameter></paramdef> 42 <paramdef>unsigned* <parameter>ret_burst</parameter></paramdef> 43 </funcprototype> 44 45 <funcprototype> 46 <funcdef>int <function>sd_event_source_is_ratelimited</function></funcdef> 47 <paramdef>sd_event_source *<parameter>source</parameter></paramdef> 48 </funcprototype> 49 50 <funcprototype> 51 <funcdef>int <function>sd_event_source_set_ratelimit_expire_callback</function></funcdef> 52 <paramdef>sd_event_source *<parameter>source</parameter></paramdef> 53 <paramdef>sd_event_handler_t<parameter>callback</parameter></paramdef> 54 </funcprototype> 55 56 </funcsynopsis> 57 </refsynopsisdiv> 58 59 <refsect1> 60 <title>Description</title> 61 62 <para><function>sd_event_source_set_ratelimit()</function> may be used to enforce rate limiting on an 63 event source. When used an event source will be temporarily turned off when it fires more often then a 64 specified burst number within a specified time interval. This is useful as simple mechanism to avoid 65 event source starvation if high priority event sources fire very frequently.</para> 66 67 <para>Pass the event source to operate on as first argument, a time interval in microseconds as second 68 argument and a maximum dispatch limit ("burst") as third parameter. Whenever the event source is 69 dispatched more often than the specified burst within the specified interval it is placed in a mode 70 similar to being disabled with 71 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> 72 and the <constant>SD_EVENT_OFF</constant> parameter. However it is disabled only temporarily – once the 73 specified interval is over regular operation resumes. It is again disabled temporarily once the specified rate 74 limiting is hit the next time. If either the interval or the burst value are specified as zero, rate 75 limiting is turned off. By default event sources do not have rate limiting enabled. Note that rate 76 limiting and disabling via <function>sd_event_source_set_enabled()</function> are independent of each 77 other, and an event source will only effect event loop wake-ups and is dispatched while it both is 78 enabled and rate limiting is not in effect.</para> 79 80 <para><function>sd_event_source_get_ratelimit()</function> may be used to query the current rate limiting 81 parameters set on the event source object <parameter>source</parameter>. The previously set interval and 82 burst vales are returned in the second and third argument.</para> 83 84 <para><function>sd_event_source_is_ratelimited()</function> may be used to query whether the event source 85 is currently affected by rate limiting, i.e. it has recently hit the rate limit and is currently 86 temporarily disabled due to that.</para> 87 88 <para><function>sd_event_source_set_ratelimit_expire_callback</function> may be used to set a callback 89 function that is invoked every time the event source leaves rate limited state. Note that function is 90 called in the same event loop iteration in which state transition occurred.</para> 91 92 <para>Rate limiting is currently implemented for I/O, timer, signal, defer and inotify event 93 sources.</para> 94 </refsect1> 95 96 <refsect1> 97 <title>Return Value</title> 98 99 <para>On success, <function>sd_event_source_set_ratelimit()</function>, 100 <function>sd_event_source_set_ratelimit_expire_callback</function> and 101 <function>sd_event_source_get_ratelimit()</function> return a non-negative integer. On failure, they return 102 a negative errno-style error code. <function>sd_event_source_is_ratelimited</function> returns zero if rate 103 limiting is currently not in effect and greater than zero if it is in effect; it returns a negative 104 errno-style error code on failure.</para> 105 106 <refsect2> 107 <title>Errors</title> 108 109 <para>Returned errors may indicate the following problems:</para> 110 111 <variablelist> 112 <varlistentry> 113 <term><constant>-EINVAL</constant></term> 114 115 <listitem><para><parameter>source</parameter> is not a valid pointer to an 116 <structname>sd_event_source</structname> object. 117 </para></listitem> 118 </varlistentry> 119 120 <varlistentry> 121 <term><constant>-ECHILD</constant></term> 122 123 <listitem><para>The event loop has been created in a different process.</para></listitem> 124 </varlistentry> 125 126 <varlistentry> 127 <term><constant>-EDOM</constant></term> 128 129 <listitem><para>It was attempted to use the rate limiting feature on an event source type that does 130 not support rate limiting.</para></listitem> 131 </varlistentry> 132 133 <varlistentry> 134 <term><constant>-ENOEXEC</constant></term> 135 136 <listitem><para><function>sd_event_source_get_ratelimit()</function> was called on an event source 137 that doesn't have rate limiting configured.</para></listitem> 138 </varlistentry> 139 140 </variablelist> 141 </refsect2> 142 </refsect1> 143 144 <xi:include href="libsystemd-pkgconfig.xml" /> 145 146 <refsect1> 147 <title>See Also</title> 148 149 <para> 150 <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 151 <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 152 <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 153 <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 154 <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 155 <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 156 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> 157 </para> 158 </refsect1> 159 160</refentry> 161