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62 62
63 // unloop was called, so exit 63 // unloop was called, so exit
64 return 0; 64 return 0;
65 } 65 }
66 66
67=head1 DESCRIPTION 67=head1 ABOUT THIS DOCUMENT
68
69This document documents the libev software package.
68 70
69The newest version of this document is also available as an html-formatted 71The newest version of this document is also available as an html-formatted
70web page you might find easier to navigate when reading it for the first 72web page you might find easier to navigate when reading it for the first
71time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>. 73time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
74
75While this document tries to be as complete as possible in documenting
76libev, its usage and the rationale behind its design, it is not a tutorial
77on event-based programming, nor will it introduce event-based programming
78with libev.
79
80Familarity with event based programming techniques in general is assumed
81throughout this document.
82
83=head1 ABOUT LIBEV
72 84
73Libev is an event loop: you register interest in certain events (such as a 85Libev is an event loop: you register interest in certain events (such as a
74file descriptor being readable or a timeout occurring), and it will manage 86file descriptor being readable or a timeout occurring), and it will manage
75these event sources and provide your program with events. 87these event sources and provide your program with events.
76 88
110name C<loop> (which is always of type C<ev_loop *>) will not have 122name C<loop> (which is always of type C<ev_loop *>) will not have
111this argument. 123this argument.
112 124
113=head2 TIME REPRESENTATION 125=head2 TIME REPRESENTATION
114 126
115Libev represents time as a single floating point number, representing the 127Libev represents time as a single floating point number, representing
116(fractional) number of seconds since the (POSIX) epoch (somewhere near 128the (fractional) number of seconds since the (POSIX) epoch (somewhere
117the beginning of 1970, details are complicated, don't ask). This type is 129near the beginning of 1970, details are complicated, don't ask). This
118called C<ev_tstamp>, which is what you should use too. It usually aliases 130type is called C<ev_tstamp>, which is what you should use too. It usually
119to the C<double> type in C, and when you need to do any calculations on 131aliases to the C<double> type in C. When you need to do any calculations
120it, you should treat it as some floating point value. Unlike the name 132on it, you should treat it as some floating point value. Unlike the name
121component C<stamp> might indicate, it is also used for time differences 133component C<stamp> might indicate, it is also used for time differences
122throughout libev. 134throughout libev.
123 135
124=head1 ERROR HANDLING 136=head1 ERROR HANDLING
125 137
632 644
633This function is rarely useful, but when some event callback runs for a 645This function is rarely useful, but when some event callback runs for a
634very long time without entering the event loop, updating libev's idea of 646very long time without entering the event loop, updating libev's idea of
635the current time is a good idea. 647the current time is a good idea.
636 648
637See also "The special problem of time updates" in the C<ev_timer> section. 649See also L<The special problem of time updates> in the C<ev_timer> section.
650
651=item ev_suspend (loop)
652
653=item ev_resume (loop)
654
655These two functions suspend and resume a loop, for use when the loop is
656not used for a while and timeouts should not be processed.
657
658A typical use case would be an interactive program such as a game: When
659the user presses C<^Z> to suspend the game and resumes it an hour later it
660would be best to handle timeouts as if no time had actually passed while
661the program was suspended. This can be achieved by calling C<ev_suspend>
662in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
663C<ev_resume> directly afterwards to resume timer processing.
664
665Effectively, all C<ev_timer> watchers will be delayed by the time spend
666between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
667will be rescheduled (that is, they will lose any events that would have
668occured while suspended).
669
670After calling C<ev_suspend> you B<must not> call I<any> function on the
671given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
672without a previous call to C<ev_suspend>.
673
674Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
675event loop time (see C<ev_now_update>).
638 676
639=item ev_loop (loop, int flags) 677=item ev_loop (loop, int flags)
640 678
641Finally, this is it, the event handler. This function usually is called 679Finally, this is it, the event handler. This function usually is called
642after you initialised all your watchers and you want to start handling 680after you initialised all your watchers and you want to start handling
726 764
727If you have a watcher you never unregister that should not keep C<ev_loop> 765If you have a watcher you never unregister that should not keep C<ev_loop>
728from returning, call ev_unref() after starting, and ev_ref() before 766from returning, call ev_unref() after starting, and ev_ref() before
729stopping it. 767stopping it.
730 768
731As an example, libev itself uses this for its internal signal pipe: It is 769As an example, libev itself uses this for its internal signal pipe: It
732not visible to the libev user and should not keep C<ev_loop> from exiting 770is not visible to the libev user and should not keep C<ev_loop> from
733if no event watchers registered by it are active. It is also an excellent 771exiting if no event watchers registered by it are active. It is also an
734way to do this for generic recurring timers or from within third-party 772excellent way to do this for generic recurring timers or from within
735libraries. Just remember to I<unref after start> and I<ref before stop> 773third-party libraries. Just remember to I<unref after start> and I<ref
736(but only if the watcher wasn't active before, or was active before, 774before stop> (but only if the watcher wasn't active before, or was active
737respectively). 775before, respectively. Note also that libev might stop watchers itself
776(e.g. non-repeating timers) in which case you have to C<ev_ref>
777in the callback).
738 778
739Example: Create a signal watcher, but keep it from keeping C<ev_loop> 779Example: Create a signal watcher, but keep it from keeping C<ev_loop>
740running when nothing else is active. 780running when nothing else is active.
741 781
742 ev_signal exitsig; 782 ev_signal exitsig;
926 966
927=item C<EV_ASYNC> 967=item C<EV_ASYNC>
928 968
929The given async watcher has been asynchronously notified (see C<ev_async>). 969The given async watcher has been asynchronously notified (see C<ev_async>).
930 970
971=item C<EV_CUSTOM>
972
973Not ever sent (or otherwise used) by libev itself, but can be freely used
974by libev users to signal watchers (e.g. via C<ev_feed_event>).
975
931=item C<EV_ERROR> 976=item C<EV_ERROR>
932 977
933An unspecified error has occurred, the watcher has been stopped. This might 978An unspecified error has occurred, the watcher has been stopped. This might
934happen because the watcher could not be properly started because libev 979happen because the watcher could not be properly started because libev
935ran out of memory, a file descriptor was found to be closed or any other 980ran out of memory, a file descriptor was found to be closed or any other
1050integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> 1095integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1051(default: C<-2>). Pending watchers with higher priority will be invoked 1096(default: C<-2>). Pending watchers with higher priority will be invoked
1052before watchers with lower priority, but priority will not keep watchers 1097before watchers with lower priority, but priority will not keep watchers
1053from being executed (except for C<ev_idle> watchers). 1098from being executed (except for C<ev_idle> watchers).
1054 1099
1055This means that priorities are I<only> used for ordering callback
1056invocation after new events have been received. This is useful, for
1057example, to reduce latency after idling, or more often, to bind two
1058watchers on the same event and make sure one is called first.
1059
1060If you need to suppress invocation when higher priority events are pending 1100If you need to suppress invocation when higher priority events are pending
1061you need to look at C<ev_idle> watchers, which provide this functionality. 1101you need to look at C<ev_idle> watchers, which provide this functionality.
1062 1102
1063You I<must not> change the priority of a watcher as long as it is active or 1103You I<must not> change the priority of a watcher as long as it is active or
1064pending. 1104pending.
1065
1066The default priority used by watchers when no priority has been set is
1067always C<0>, which is supposed to not be too high and not be too low :).
1068 1105
1069Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is 1106Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1070fine, as long as you do not mind that the priority value you query might 1107fine, as long as you do not mind that the priority value you query might
1071or might not have been clamped to the valid range. 1108or might not have been clamped to the valid range.
1109
1110The default priority used by watchers when no priority has been set is
1111always C<0>, which is supposed to not be too high and not be too low :).
1112
1113See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1114priorities.
1072 1115
1073=item ev_invoke (loop, ev_TYPE *watcher, int revents) 1116=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1074 1117
1075Invoke the C<watcher> with the given C<loop> and C<revents>. Neither 1118Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1076C<loop> nor C<revents> need to be valid as long as the watcher callback 1119C<loop> nor C<revents> need to be valid as long as the watcher callback
1151 t2_cb (EV_P_ ev_timer *w, int revents) 1194 t2_cb (EV_P_ ev_timer *w, int revents)
1152 { 1195 {
1153 struct my_biggy big = (struct my_biggy * 1196 struct my_biggy big = (struct my_biggy *
1154 (((char *)w) - offsetof (struct my_biggy, t2)); 1197 (((char *)w) - offsetof (struct my_biggy, t2));
1155 } 1198 }
1199
1200=head2 WATCHER PRIORITY MODELS
1201
1202Many event loops support I<watcher priorities>, which are usually small
1203integers that influence the ordering of event callback invocation
1204between watchers in some way, all else being equal.
1205
1206In libev, Watcher priorities can be set using C<ev_set_priority>. See its
1207description for the more technical details such as the actual priority
1208range.
1209
1210There are two common ways how these these priorities are being interpreted
1211by event loops:
1212
1213In the more common lock-out model, higher priorities "lock out" invocation
1214of lower priority watchers, which means as long as higher priority
1215watchers receive events, lower priority watchers are not being invoked.
1216
1217The less common only-for-ordering model uses priorities solely to order
1218callback invocation within a single event loop iteration: Higher priority
1219watchers are invoked before lower priority ones, but they all get invoked
1220before polling for new events.
1221
1222Libev uses the second (only-for-ordering) model for all its watchers
1223except for idle watchers (which use the lock-out model).
1224
1225The rationale behind this is that implementing the lock-out model for
1226watchers is not well supported by most kernel interfaces, and most event
1227libraries will just poll for the same events again and again as long as
1228their callbacks have not been executed, which is very inefficient in the
1229common case of one high-priority watcher locking out a mass of lower
1230priority ones.
1231
1232Static (ordering) priorities are most useful when you have two or more
1233watchers handling the same resource: a typical usage example is having an
1234C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
1235timeouts. Under load, data might be received while the program handles
1236other jobs, but since timers normally get invoked first, the timeout
1237handler will be executed before checking for data. In that case, giving
1238the timer a lower priority than the I/O watcher ensures that I/O will be
1239handled first even under adverse conditions (which is usually, but not
1240always, what you want).
1241
1242Since idle watchers use the "lock-out" model, meaning that idle watchers
1243will only be executed when no same or higher priority watchers have
1244received events, they can be used to implement the "lock-out" model when
1245required.
1246
1247For example, to emulate how many other event libraries handle priorities,
1248you can associate an C<ev_idle> watcher to each such watcher, and in
1249the normal watcher callback, you just start the idle watcher. The real
1250processing is done in the idle watcher callback. This causes libev to
1251continously poll and process kernel event data for the watcher, but when
1252the lock-out case is known to be rare (which in turn is rare :), this is
1253workable.
1254
1255Usually, however, the lock-out model implemented that way will perform
1256miserably under the type of load it was designed to handle. In that case,
1257it might be preferable to stop the real watcher before starting the
1258idle watcher, so the kernel will not have to process the event in case
1259the actual processing will be delayed for considerable time.
1260
1261Here is an example of an I/O watcher that should run at a strictly lower
1262priority than the default, and which should only process data when no
1263other events are pending:
1264
1265 ev_idle idle; // actual processing watcher
1266 ev_io io; // actual event watcher
1267
1268 static void
1269 io_cb (EV_P_ ev_io *w, int revents)
1270 {
1271 // stop the I/O watcher, we received the event, but
1272 // are not yet ready to handle it.
1273 ev_io_stop (EV_A_ w);
1274
1275 // start the idle watcher to ahndle the actual event.
1276 // it will not be executed as long as other watchers
1277 // with the default priority are receiving events.
1278 ev_idle_start (EV_A_ &idle);
1279 }
1280
1281 static void
1282 idle-cb (EV_P_ ev_idle *w, int revents)
1283 {
1284 // actual processing
1285 read (STDIN_FILENO, ...);
1286
1287 // have to start the I/O watcher again, as
1288 // we have handled the event
1289 ev_io_start (EV_P_ &io);
1290 }
1291
1292 // initialisation
1293 ev_idle_init (&idle, idle_cb);
1294 ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1295 ev_io_start (EV_DEFAULT_ &io);
1296
1297In the "real" world, it might also be beneficial to start a timer, so that
1298low-priority connections can not be locked out forever under load. This
1299enables your program to keep a lower latency for important connections
1300during short periods of high load, while not completely locking out less
1301important ones.
1156 1302
1157 1303
1158=head1 WATCHER TYPES 1304=head1 WATCHER TYPES
1159 1305
1160This section describes each watcher in detail, but will not repeat 1306This section describes each watcher in detail, but will not repeat
1317year, it will still time out after (roughly) one hour. "Roughly" because 1463year, it will still time out after (roughly) one hour. "Roughly" because
1318detecting time jumps is hard, and some inaccuracies are unavoidable (the 1464detecting time jumps is hard, and some inaccuracies are unavoidable (the
1319monotonic clock option helps a lot here). 1465monotonic clock option helps a lot here).
1320 1466
1321The callback is guaranteed to be invoked only I<after> its timeout has 1467The callback is guaranteed to be invoked only I<after> its timeout has
1322passed, but if multiple timers become ready during the same loop iteration 1468passed. If multiple timers become ready during the same loop iteration
1323then order of execution is undefined. 1469then the ones with earlier time-out values are invoked before ones with
1470later time-out values (but this is no longer true when a callback calls
1471C<ev_loop> recursively).
1324 1472
1325=head3 Be smart about timeouts 1473=head3 Be smart about timeouts
1326 1474
1327Many real-world problems involve some kind of timeout, usually for error 1475Many real-world problems involve some kind of timeout, usually for error
1328recovery. A typical example is an HTTP request - if the other side hangs, 1476recovery. A typical example is an HTTP request - if the other side hangs,
1547If the timer is started but non-repeating, stop it (as if it timed out). 1695If the timer is started but non-repeating, stop it (as if it timed out).
1548 1696
1549If the timer is repeating, either start it if necessary (with the 1697If the timer is repeating, either start it if necessary (with the
1550C<repeat> value), or reset the running timer to the C<repeat> value. 1698C<repeat> value), or reset the running timer to the C<repeat> value.
1551 1699
1552This sounds a bit complicated, see "Be smart about timeouts", above, for a 1700This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1553usage example. 1701usage example.
1554 1702
1555=item ev_tstamp repeat [read-write] 1703=item ev_tstamp repeat [read-write]
1556 1704
1557The current C<repeat> value. Will be used each time the watcher times out 1705The current C<repeat> value. Will be used each time the watcher times out
1596=head2 C<ev_periodic> - to cron or not to cron? 1744=head2 C<ev_periodic> - to cron or not to cron?
1597 1745
1598Periodic watchers are also timers of a kind, but they are very versatile 1746Periodic watchers are also timers of a kind, but they are very versatile
1599(and unfortunately a bit complex). 1747(and unfortunately a bit complex).
1600 1748
1601Unlike C<ev_timer>'s, they are not based on real time (or relative time) 1749Unlike C<ev_timer>, periodic watchers are not based on real time (or
1602but on wall clock time (absolute time). You can tell a periodic watcher 1750relative time, the physical time that passes) but on wall clock time
1603to trigger after some specific point in time. For example, if you tell a 1751(absolute time, the thing you can read on your calender or clock). The
1604periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now () 1752difference is that wall clock time can run faster or slower than real
1605+ 10.>, that is, an absolute time not a delay) and then reset your system 1753time, and time jumps are not uncommon (e.g. when you adjust your
1606clock to January of the previous year, then it will take more than year 1754wrist-watch).
1607to trigger the event (unlike an C<ev_timer>, which would still trigger
1608roughly 10 seconds later as it uses a relative timeout).
1609 1755
1756You can tell a periodic watcher to trigger after some specific point
1757in time: for example, if you tell a periodic watcher to trigger "in 10
1758seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
1759not a delay) and then reset your system clock to January of the previous
1760year, then it will take a year or more to trigger the event (unlike an
1761C<ev_timer>, which would still trigger roughly 10 seconds after starting
1762it, as it uses a relative timeout).
1763
1610C<ev_periodic>s can also be used to implement vastly more complex timers, 1764C<ev_periodic> watchers can also be used to implement vastly more complex
1611such as triggering an event on each "midnight, local time", or other 1765timers, such as triggering an event on each "midnight, local time", or
1612complicated rules. 1766other complicated rules. This cannot be done with C<ev_timer> watchers, as
1767those cannot react to time jumps.
1613 1768
1614As with timers, the callback is guaranteed to be invoked only when the 1769As with timers, the callback is guaranteed to be invoked only when the
1615time (C<at>) has passed, but if multiple periodic timers become ready 1770point in time where it is supposed to trigger has passed. If multiple
1616during the same loop iteration, then order of execution is undefined. 1771timers become ready during the same loop iteration then the ones with
1772earlier time-out values are invoked before ones with later time-out values
1773(but this is no longer true when a callback calls C<ev_loop> recursively).
1617 1774
1618=head3 Watcher-Specific Functions and Data Members 1775=head3 Watcher-Specific Functions and Data Members
1619 1776
1620=over 4 1777=over 4
1621 1778
1622=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) 1779=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1623 1780
1624=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) 1781=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1625 1782
1626Lots of arguments, lets sort it out... There are basically three modes of 1783Lots of arguments, let's sort it out... There are basically three modes of
1627operation, and we will explain them from simplest to most complex: 1784operation, and we will explain them from simplest to most complex:
1628 1785
1629=over 4 1786=over 4
1630 1787
1631=item * absolute timer (at = time, interval = reschedule_cb = 0) 1788=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1632 1789
1633In this configuration the watcher triggers an event after the wall clock 1790In this configuration the watcher triggers an event after the wall clock
1634time C<at> has passed. It will not repeat and will not adjust when a time 1791time C<offset> has passed. It will not repeat and will not adjust when a
1635jump occurs, that is, if it is to be run at January 1st 2011 then it will 1792time jump occurs, that is, if it is to be run at January 1st 2011 then it
1636only run when the system clock reaches or surpasses this time. 1793will be stopped and invoked when the system clock reaches or surpasses
1794this point in time.
1637 1795
1638=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) 1796=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1639 1797
1640In this mode the watcher will always be scheduled to time out at the next 1798In this mode the watcher will always be scheduled to time out at the next
1641C<at + N * interval> time (for some integer N, which can also be negative) 1799C<offset + N * interval> time (for some integer N, which can also be
1642and then repeat, regardless of any time jumps. 1800negative) and then repeat, regardless of any time jumps. The C<offset>
1801argument is merely an offset into the C<interval> periods.
1643 1802
1644This can be used to create timers that do not drift with respect to the 1803This can be used to create timers that do not drift with respect to the
1645system clock, for example, here is a C<ev_periodic> that triggers each 1804system clock, for example, here is an C<ev_periodic> that triggers each
1646hour, on the hour: 1805hour, on the hour (with respect to UTC):
1647 1806
1648 ev_periodic_set (&periodic, 0., 3600., 0); 1807 ev_periodic_set (&periodic, 0., 3600., 0);
1649 1808
1650This doesn't mean there will always be 3600 seconds in between triggers, 1809This doesn't mean there will always be 3600 seconds in between triggers,
1651but only that the callback will be called when the system time shows a 1810but only that the callback will be called when the system time shows a
1652full hour (UTC), or more correctly, when the system time is evenly divisible 1811full hour (UTC), or more correctly, when the system time is evenly divisible
1653by 3600. 1812by 3600.
1654 1813
1655Another way to think about it (for the mathematically inclined) is that 1814Another way to think about it (for the mathematically inclined) is that
1656C<ev_periodic> will try to run the callback in this mode at the next possible 1815C<ev_periodic> will try to run the callback in this mode at the next possible
1657time where C<time = at (mod interval)>, regardless of any time jumps. 1816time where C<time = offset (mod interval)>, regardless of any time jumps.
1658 1817
1659For numerical stability it is preferable that the C<at> value is near 1818For numerical stability it is preferable that the C<offset> value is near
1660C<ev_now ()> (the current time), but there is no range requirement for 1819C<ev_now ()> (the current time), but there is no range requirement for
1661this value, and in fact is often specified as zero. 1820this value, and in fact is often specified as zero.
1662 1821
1663Note also that there is an upper limit to how often a timer can fire (CPU 1822Note also that there is an upper limit to how often a timer can fire (CPU
1664speed for example), so if C<interval> is very small then timing stability 1823speed for example), so if C<interval> is very small then timing stability
1665will of course deteriorate. Libev itself tries to be exact to be about one 1824will of course deteriorate. Libev itself tries to be exact to be about one
1666millisecond (if the OS supports it and the machine is fast enough). 1825millisecond (if the OS supports it and the machine is fast enough).
1667 1826
1668=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback) 1827=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1669 1828
1670In this mode the values for C<interval> and C<at> are both being 1829In this mode the values for C<interval> and C<offset> are both being
1671ignored. Instead, each time the periodic watcher gets scheduled, the 1830ignored. Instead, each time the periodic watcher gets scheduled, the
1672reschedule callback will be called with the watcher as first, and the 1831reschedule callback will be called with the watcher as first, and the
1673current time as second argument. 1832current time as second argument.
1674 1833
1675NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, 1834NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1676ever, or make ANY event loop modifications whatsoever>. 1835or make ANY other event loop modifications whatsoever, unless explicitly
1836allowed by documentation here>.
1677 1837
1678If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop 1838If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1679it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the 1839it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1680only event loop modification you are allowed to do). 1840only event loop modification you are allowed to do).
1681 1841
1711a different time than the last time it was called (e.g. in a crond like 1871a different time than the last time it was called (e.g. in a crond like
1712program when the crontabs have changed). 1872program when the crontabs have changed).
1713 1873
1714=item ev_tstamp ev_periodic_at (ev_periodic *) 1874=item ev_tstamp ev_periodic_at (ev_periodic *)
1715 1875
1716When active, returns the absolute time that the watcher is supposed to 1876When active, returns the absolute time that the watcher is supposed
1717trigger next. 1877to trigger next. This is not the same as the C<offset> argument to
1878C<ev_periodic_set>, but indeed works even in interval and manual
1879rescheduling modes.
1718 1880
1719=item ev_tstamp offset [read-write] 1881=item ev_tstamp offset [read-write]
1720 1882
1721When repeating, this contains the offset value, otherwise this is the 1883When repeating, this contains the offset value, otherwise this is the
1722absolute point in time (the C<at> value passed to C<ev_periodic_set>). 1884absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
1885although libev might modify this value for better numerical stability).
1723 1886
1724Can be modified any time, but changes only take effect when the periodic 1887Can be modified any time, but changes only take effect when the periodic
1725timer fires or C<ev_periodic_again> is being called. 1888timer fires or C<ev_periodic_again> is being called.
1726 1889
1727=item ev_tstamp interval [read-write] 1890=item ev_tstamp interval [read-write]
2179 2342
2180=head3 Watcher-Specific Functions and Data Members 2343=head3 Watcher-Specific Functions and Data Members
2181 2344
2182=over 4 2345=over 4
2183 2346
2184=item ev_idle_init (ev_signal *, callback) 2347=item ev_idle_init (ev_idle *, callback)
2185 2348
2186Initialises and configures the idle watcher - it has no parameters of any 2349Initialises and configures the idle watcher - it has no parameters of any
2187kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, 2350kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2188believe me. 2351believe me.
2189 2352
2545event loop blocks next and before C<ev_check> watchers are being called, 2708event loop blocks next and before C<ev_check> watchers are being called,
2546and only in the child after the fork. If whoever good citizen calling 2709and only in the child after the fork. If whoever good citizen calling
2547C<ev_default_fork> cheats and calls it in the wrong process, the fork 2710C<ev_default_fork> cheats and calls it in the wrong process, the fork
2548handlers will be invoked, too, of course. 2711handlers will be invoked, too, of course.
2549 2712
2713=head3 The special problem of life after fork - how is it possible?
2714
2715Most uses of C<fork()> consist of forking, then some simple calls to ste
2716up/change the process environment, followed by a call to C<exec()>. This
2717sequence should be handled by libev without any problems.
2718
2719This changes when the application actually wants to do event handling
2720in the child, or both parent in child, in effect "continuing" after the
2721fork.
2722
2723The default mode of operation (for libev, with application help to detect
2724forks) is to duplicate all the state in the child, as would be expected
2725when I<either> the parent I<or> the child process continues.
2726
2727When both processes want to continue using libev, then this is usually the
2728wrong result. In that case, usually one process (typically the parent) is
2729supposed to continue with all watchers in place as before, while the other
2730process typically wants to start fresh, i.e. without any active watchers.
2731
2732The cleanest and most efficient way to achieve that with libev is to
2733simply create a new event loop, which of course will be "empty", and
2734use that for new watchers. This has the advantage of not touching more
2735memory than necessary, and thus avoiding the copy-on-write, and the
2736disadvantage of having to use multiple event loops (which do not support
2737signal watchers).
2738
2739When this is not possible, or you want to use the default loop for
2740other reasons, then in the process that wants to start "fresh", call
2741C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
2742the default loop will "orphan" (not stop) all registered watchers, so you
2743have to be careful not to execute code that modifies those watchers. Note
2744also that in that case, you have to re-register any signal watchers.
2745
2550=head3 Watcher-Specific Functions and Data Members 2746=head3 Watcher-Specific Functions and Data Members
2551 2747
2552=over 4 2748=over 4
2553 2749
2554=item ev_fork_init (ev_signal *, callback) 2750=item ev_fork_init (ev_signal *, callback)
2682an C<EV_ASYNC> event on the watcher into the event loop. Unlike 2878an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2683C<ev_feed_event>, this call is safe to do from other threads, signal or 2879C<ev_feed_event>, this call is safe to do from other threads, signal or
2684similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding 2880similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2685section below on what exactly this means). 2881section below on what exactly this means).
2686 2882
2883Note that, as with other watchers in libev, multiple events might get
2884compressed into a single callback invocation (another way to look at this
2885is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
2886reset when the event loop detects that).
2887
2687This call incurs the overhead of a system call only once per loop iteration, 2888This call incurs the overhead of a system call only once per event loop
2688so while the overhead might be noticeable, it doesn't apply to repeated 2889iteration, so while the overhead might be noticeable, it doesn't apply to
2689calls to C<ev_async_send>. 2890repeated calls to C<ev_async_send> for the same event loop.
2690 2891
2691=item bool = ev_async_pending (ev_async *) 2892=item bool = ev_async_pending (ev_async *)
2692 2893
2693Returns a non-zero value when C<ev_async_send> has been called on the 2894Returns a non-zero value when C<ev_async_send> has been called on the
2694watcher but the event has not yet been processed (or even noted) by the 2895watcher but the event has not yet been processed (or even noted) by the
2697C<ev_async_send> sets a flag in the watcher and wakes up the loop. When 2898C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2698the loop iterates next and checks for the watcher to have become active, 2899the loop iterates next and checks for the watcher to have become active,
2699it will reset the flag again. C<ev_async_pending> can be used to very 2900it will reset the flag again. C<ev_async_pending> can be used to very
2700quickly check whether invoking the loop might be a good idea. 2901quickly check whether invoking the loop might be a good idea.
2701 2902
2702Not that this does I<not> check whether the watcher itself is pending, only 2903Not that this does I<not> check whether the watcher itself is pending,
2703whether it has been requested to make this watcher pending. 2904only whether it has been requested to make this watcher pending: there
2905is a time window between the event loop checking and resetting the async
2906notification, and the callback being invoked.
2704 2907
2705=back 2908=back
2706 2909
2707 2910
2708=head1 OTHER FUNCTIONS 2911=head1 OTHER FUNCTIONS
3012L<http://software.schmorp.de/pkg/EV>. 3215L<http://software.schmorp.de/pkg/EV>.
3013 3216
3014=item Python 3217=item Python
3015 3218
3016Python bindings can be found at L<http://code.google.com/p/pyev/>. It 3219Python bindings can be found at L<http://code.google.com/p/pyev/>. It
3017seems to be quite complete and well-documented. Note, however, that the 3220seems to be quite complete and well-documented.
3018patch they require for libev is outright dangerous as it breaks the ABI
3019for everybody else, and therefore, should never be applied in an installed
3020libev (if python requires an incompatible ABI then it needs to embed
3021libev).
3022 3221
3023=item Ruby 3222=item Ruby
3024 3223
3025Tony Arcieri has written a ruby extension that offers access to a subset 3224Tony Arcieri has written a ruby extension that offers access to a subset
3026of the libev API and adds file handle abstractions, asynchronous DNS and 3225of the libev API and adds file handle abstractions, asynchronous DNS and
3027more on top of it. It can be found via gem servers. Its homepage is at 3226more on top of it. It can be found via gem servers. Its homepage is at
3028L<http://rev.rubyforge.org/>. 3227L<http://rev.rubyforge.org/>.
3029 3228
3030Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190> 3229Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
3031makes rev work even on mingw. 3230makes rev work even on mingw.
3231
3232=item Haskell
3233
3234A haskell binding to libev is available at
3235L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3032 3236
3033=item D 3237=item D
3034 3238
3035Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to 3239Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3036be found at L<http://proj.llucax.com.ar/wiki/evd>. 3240be found at L<http://proj.llucax.com.ar/wiki/evd>.
3935involves iterating over all running async watchers or all signal numbers. 4139involves iterating over all running async watchers or all signal numbers.
3936 4140
3937=back 4141=back
3938 4142
3939 4143
4144=head1 GLOSSARY
4145
4146=over 4
4147
4148=item active
4149
4150A watcher is active as long as it has been started (has been attached to
4151an event loop) but not yet stopped (disassociated from the event loop).
4152
4153=item application
4154
4155In this document, an application is whatever is using libev.
4156
4157=item callback
4158
4159The address of a function that is called when some event has been
4160detected. Callbacks are being passed the event loop, the watcher that
4161received the event, and the actual event bitset.
4162
4163=item callback invocation
4164
4165The act of calling the callback associated with a watcher.
4166
4167=item event
4168
4169A change of state of some external event, such as data now being available
4170for reading on a file descriptor, time having passed or simply not having
4171any other events happening anymore.
4172
4173In libev, events are represented as single bits (such as C<EV_READ> or
4174C<EV_TIMEOUT>).
4175
4176=item event library
4177
4178A software package implementing an event model and loop.
4179
4180=item event loop
4181
4182An entity that handles and processes external events and converts them
4183into callback invocations.
4184
4185=item event model
4186
4187The model used to describe how an event loop handles and processes
4188watchers and events.
4189
4190=item pending
4191
4192A watcher is pending as soon as the corresponding event has been detected,
4193and stops being pending as soon as the watcher will be invoked or its
4194pending status is explicitly cleared by the application.
4195
4196A watcher can be pending, but not active. Stopping a watcher also clears
4197its pending status.
4198
4199=item real time
4200
4201The physical time that is observed. It is apparently strictly monotonic :)
4202
4203=item wall-clock time
4204
4205The time and date as shown on clocks. Unlike real time, it can actually
4206be wrong and jump forwards and backwards, e.g. when the you adjust your
4207clock.
4208
4209=item watcher
4210
4211A data structure that describes interest in certain events. Watchers need
4212to be started (attached to an event loop) before they can receive events.
4213
4214=item watcher invocation
4215
4216The act of calling the callback associated with a watcher.
4217
4218=back
4219
3940=head1 AUTHOR 4220=head1 AUTHOR
3941 4221
3942Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson. 4222Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3943 4223

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