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4 | <head> |
4 | <head> |
5 | <title>libev</title> |
5 | <title>libev</title> |
6 | <meta name="description" content="Pod documentation for libev" /> |
6 | <meta name="description" content="Pod documentation for libev" /> |
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14 | <!-- INDEX START --> |
14 | <!-- INDEX START --> |
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27 | <ul><li><a href="#GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</a></li> |
27 | <ul><li><a href="#GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</a></li> |
28 | <li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> |
28 | <li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> |
29 | </ul> |
29 | </ul> |
30 | </li> |
30 | </li> |
31 | <li><a href="#WATCHER_TYPES">WATCHER TYPES</a> |
31 | <li><a href="#WATCHER_TYPES">WATCHER TYPES</a> |
32 | <ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</a></li> |
32 | <ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</a> |
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33 | <ul><li><a href="#The_special_problem_of_disappearing_">The special problem of disappearing file descriptors</a></li> |
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34 | </ul> |
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35 | </li> |
33 | <li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</a></li> |
36 | <li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</a></li> |
34 | <li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</a></li> |
37 | <li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</a></li> |
35 | <li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</a></li> |
38 | <li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</a></li> |
36 | <li><a href="#code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</a></li> |
39 | <li><a href="#code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</a></li> |
37 | <li><a href="#code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</a></li> |
40 | <li><a href="#code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</a></li> |
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185 | you actually want to know.</p> |
188 | you actually want to know.</p> |
186 | </dd> |
189 | </dd> |
187 | <dt>int ev_version_major ()</dt> |
190 | <dt>int ev_version_major ()</dt> |
188 | <dt>int ev_version_minor ()</dt> |
191 | <dt>int ev_version_minor ()</dt> |
189 | <dd> |
192 | <dd> |
190 | <p>You can find out the major and minor version numbers of the library |
193 | <p>You can find out the major and minor ABI version numbers of the library |
191 | you linked against by calling the functions <code>ev_version_major</code> and |
194 | you linked against by calling the functions <code>ev_version_major</code> and |
192 | <code>ev_version_minor</code>. If you want, you can compare against the global |
195 | <code>ev_version_minor</code>. If you want, you can compare against the global |
193 | symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the |
196 | symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the |
194 | version of the library your program was compiled against.</p> |
197 | version of the library your program was compiled against.</p> |
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198 | <p>These version numbers refer to the ABI version of the library, not the |
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199 | release version.</p> |
195 | <p>Usually, it's a good idea to terminate if the major versions mismatch, |
200 | <p>Usually, it's a good idea to terminate if the major versions mismatch, |
196 | as this indicates an incompatible change. Minor versions are usually |
201 | as this indicates an incompatible change. Minor versions are usually |
197 | compatible to older versions, so a larger minor version alone is usually |
202 | compatible to older versions, so a larger minor version alone is usually |
198 | not a problem.</p> |
203 | not a problem.</p> |
199 | <p>Example: Make sure we haven't accidentally been linked against the wrong |
204 | <p>Example: Make sure we haven't accidentally been linked against the wrong |
200 | version.</p> |
205 | version.</p> |
201 | <pre> assert (("libev version mismatch", |
206 | <pre> assert (("libev version mismatch", |
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939 | <p>If you cannot run the fd in non-blocking mode (for example you should not |
944 | <p>If you cannot run the fd in non-blocking mode (for example you should not |
940 | play around with an Xlib connection), then you have to seperately re-test |
945 | play around with an Xlib connection), then you have to seperately re-test |
941 | whether a file descriptor is really ready with a known-to-be good interface |
946 | whether a file descriptor is really ready with a known-to-be good interface |
942 | such as poll (fortunately in our Xlib example, Xlib already does this on |
947 | such as poll (fortunately in our Xlib example, Xlib already does this on |
943 | its own, so its quite safe to use).</p> |
948 | its own, so its quite safe to use).</p> |
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949 | |
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950 | </div> |
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951 | <h3 id="The_special_problem_of_disappearing_">The special problem of disappearing file descriptors</h3> |
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952 | <div id="The_special_problem_of_disappearing_-2"> |
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953 | <p>Some backends (e.g kqueue, epoll) need to be told about closing a file |
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954 | descriptor (either by calling <code>close</code> explicitly or by any other means, |
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955 | such as <code>dup</code>). The reason is that you register interest in some file |
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956 | descriptor, but when it goes away, the operating system will silently drop |
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957 | this interest. If another file descriptor with the same number then is |
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958 | registered with libev, there is no efficient way to see that this is, in |
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959 | fact, a different file descriptor.</p> |
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960 | <p>To avoid having to explicitly tell libev about such cases, libev follows |
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961 | the following policy: Each time <code>ev_io_set</code> is being called, libev |
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962 | will assume that this is potentially a new file descriptor, otherwise |
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963 | it is assumed that the file descriptor stays the same. That means that |
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964 | you <i>have</i> to call <code>ev_io_set</code> (or <code>ev_io_init</code>) when you change the |
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965 | descriptor even if the file descriptor number itself did not change.</p> |
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966 | <p>This is how one would do it normally anyway, the important point is that |
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967 | the libev application should not optimise around libev but should leave |
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968 | optimisations to libev.</p> |
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969 | |
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970 | |
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971 | |
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972 | |
944 | <dl> |
973 | <dl> |
945 | <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> |
974 | <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> |
946 | <dt>ev_io_set (ev_io *, int fd, int events)</dt> |
975 | <dt>ev_io_set (ev_io *, int fd, int events)</dt> |
947 | <dd> |
976 | <dd> |
948 | <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> is the file descriptor to |
977 | <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> is the file descriptor to |
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1097 | but on wallclock time (absolute time). You can tell a periodic watcher |
1126 | but on wallclock time (absolute time). You can tell a periodic watcher |
1098 | to trigger "at" some specific point in time. For example, if you tell a |
1127 | to trigger "at" some specific point in time. For example, if you tell a |
1099 | periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now () |
1128 | periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now () |
1100 | + 10.</code>) and then reset your system clock to the last year, then it will |
1129 | + 10.</code>) and then reset your system clock to the last year, then it will |
1101 | take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger |
1130 | take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger |
1102 | roughly 10 seconds later and of course not if you reset your system time |
1131 | roughly 10 seconds later).</p> |
1103 | again).</p> |
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1104 | <p>They can also be used to implement vastly more complex timers, such as |
1132 | <p>They can also be used to implement vastly more complex timers, such as |
1105 | triggering an event on eahc midnight, local time.</p> |
1133 | triggering an event on each midnight, local time or other, complicated, |
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1134 | rules.</p> |
1106 | <p>As with timers, the callback is guarenteed to be invoked only when the |
1135 | <p>As with timers, the callback is guarenteed to be invoked only when the |
1107 | time (<code>at</code>) has been passed, but if multiple periodic timers become ready |
1136 | time (<code>at</code>) has been passed, but if multiple periodic timers become ready |
1108 | during the same loop iteration then order of execution is undefined.</p> |
1137 | during the same loop iteration then order of execution is undefined.</p> |
1109 | <dl> |
1138 | <dl> |
1110 | <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt> |
1139 | <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt> |
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1112 | <dd> |
1141 | <dd> |
1113 | <p>Lots of arguments, lets sort it out... There are basically three modes of |
1142 | <p>Lots of arguments, lets sort it out... There are basically three modes of |
1114 | operation, and we will explain them from simplest to complex:</p> |
1143 | operation, and we will explain them from simplest to complex:</p> |
1115 | <p> |
1144 | <p> |
1116 | <dl> |
1145 | <dl> |
1117 | <dt>* absolute timer (interval = reschedule_cb = 0)</dt> |
1146 | <dt>* absolute timer (at = time, interval = reschedule_cb = 0)</dt> |
1118 | <dd> |
1147 | <dd> |
1119 | <p>In this configuration the watcher triggers an event at the wallclock time |
1148 | <p>In this configuration the watcher triggers an event at the wallclock time |
1120 | <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs, |
1149 | <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs, |
1121 | that is, if it is to be run at January 1st 2011 then it will run when the |
1150 | that is, if it is to be run at January 1st 2011 then it will run when the |
1122 | system time reaches or surpasses this time.</p> |
1151 | system time reaches or surpasses this time.</p> |
1123 | </dd> |
1152 | </dd> |
1124 | <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt> |
1153 | <dt>* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)</dt> |
1125 | <dd> |
1154 | <dd> |
1126 | <p>In this mode the watcher will always be scheduled to time out at the next |
1155 | <p>In this mode the watcher will always be scheduled to time out at the next |
1127 | <code>at + N * interval</code> time (for some integer N) and then repeat, regardless |
1156 | <code>at + N * interval</code> time (for some integer N, which can also be negative) |
1128 | of any time jumps.</p> |
1157 | and then repeat, regardless of any time jumps.</p> |
1129 | <p>This can be used to create timers that do not drift with respect to system |
1158 | <p>This can be used to create timers that do not drift with respect to system |
1130 | time:</p> |
1159 | time:</p> |
1131 | <pre> ev_periodic_set (&periodic, 0., 3600., 0); |
1160 | <pre> ev_periodic_set (&periodic, 0., 3600., 0); |
1132 | |
1161 | |
1133 | </pre> |
1162 | </pre> |
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1136 | full hour (UTC), or more correctly, when the system time is evenly divisible |
1165 | full hour (UTC), or more correctly, when the system time is evenly divisible |
1137 | by 3600.</p> |
1166 | by 3600.</p> |
1138 | <p>Another way to think about it (for the mathematically inclined) is that |
1167 | <p>Another way to think about it (for the mathematically inclined) is that |
1139 | <code>ev_periodic</code> will try to run the callback in this mode at the next possible |
1168 | <code>ev_periodic</code> will try to run the callback in this mode at the next possible |
1140 | time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p> |
1169 | time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p> |
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1170 | <p>For numerical stability it is preferable that the <code>at</code> value is near |
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1171 | <code>ev_now ()</code> (the current time), but there is no range requirement for |
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1172 | this value.</p> |
1141 | </dd> |
1173 | </dd> |
1142 | <dt>* manual reschedule mode (reschedule_cb = callback)</dt> |
1174 | <dt>* manual reschedule mode (at and interval ignored, reschedule_cb = callback)</dt> |
1143 | <dd> |
1175 | <dd> |
1144 | <p>In this mode the values for <code>interval</code> and <code>at</code> are both being |
1176 | <p>In this mode the values for <code>interval</code> and <code>at</code> are both being |
1145 | ignored. Instead, each time the periodic watcher gets scheduled, the |
1177 | ignored. Instead, each time the periodic watcher gets scheduled, the |
1146 | reschedule callback will be called with the watcher as first, and the |
1178 | reschedule callback will be called with the watcher as first, and the |
1147 | current time as second argument.</p> |
1179 | current time as second argument.</p> |
1148 | <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher, |
1180 | <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher, |
1149 | ever, or make any event loop modifications</i>. If you need to stop it, |
1181 | ever, or make any event loop modifications</i>. If you need to stop it, |
1150 | return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by |
1182 | return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by |
1151 | starting a prepare watcher).</p> |
1183 | starting an <code>ev_prepare</code> watcher, which is legal).</p> |
1152 | <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
1184 | <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
1153 | ev_tstamp now)</code>, e.g.:</p> |
1185 | ev_tstamp now)</code>, e.g.:</p> |
1154 | <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
1186 | <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
1155 | { |
1187 | { |
1156 | return now + 60.; |
1188 | return now + 60.; |
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1176 | <dd> |
1208 | <dd> |
1177 | <p>Simply stops and restarts the periodic watcher again. This is only useful |
1209 | <p>Simply stops and restarts the periodic watcher again. This is only useful |
1178 | when you changed some parameters or the reschedule callback would return |
1210 | when you changed some parameters or the reschedule callback would return |
1179 | a different time than the last time it was called (e.g. in a crond like |
1211 | a different time than the last time it was called (e.g. in a crond like |
1180 | program when the crontabs have changed).</p> |
1212 | program when the crontabs have changed).</p> |
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1213 | </dd> |
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1214 | <dt>ev_tstamp offset [read-write]</dt> |
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1215 | <dd> |
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1216 | <p>When repeating, this contains the offset value, otherwise this is the |
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1217 | absolute point in time (the <code>at</code> value passed to <code>ev_periodic_set</code>).</p> |
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1218 | <p>Can be modified any time, but changes only take effect when the periodic |
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1219 | timer fires or <code>ev_periodic_again</code> is being called.</p> |
1181 | </dd> |
1220 | </dd> |
1182 | <dt>ev_tstamp interval [read-write]</dt> |
1221 | <dt>ev_tstamp interval [read-write]</dt> |
1183 | <dd> |
1222 | <dd> |
1184 | <p>The current interval value. Can be modified any time, but changes only |
1223 | <p>The current interval value. Can be modified any time, but changes only |
1185 | take effect when the periodic timer fires or <code>ev_periodic_again</code> is being |
1224 | take effect when the periodic timer fires or <code>ev_periodic_again</code> is being |