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Revision 1.77 by root, Sat Dec 8 22:11:14 2007 UTC vs.
Revision 1.78 by root, Sun Dec 9 19:42:57 2007 UTC

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1074but on wallclock time (absolute time). You can tell a periodic watcher 1074but on wallclock time (absolute time). You can tell a periodic watcher
1075to trigger "at" some specific point in time. For example, if you tell a 1075to trigger "at" some specific point in time. For example, if you tell a
1076periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now () 1076periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
1077+ 10.>) and then reset your system clock to the last year, then it will 1077+ 10.>) and then reset your system clock to the last year, then it will
1078take a year to trigger the event (unlike an C<ev_timer>, which would trigger 1078take a year to trigger the event (unlike an C<ev_timer>, which would trigger
1079roughly 10 seconds later and of course not if you reset your system time 1079roughly 10 seconds later).
1080again).
1081 1080
1082They can also be used to implement vastly more complex timers, such as 1081They can also be used to implement vastly more complex timers, such as
1083triggering an event on eahc midnight, local time. 1082triggering an event on each midnight, local time or other, complicated,
1083rules.
1084 1084
1085As with timers, the callback is guarenteed to be invoked only when the 1085As with timers, the callback is guarenteed to be invoked only when the
1086time (C<at>) has been passed, but if multiple periodic timers become ready 1086time (C<at>) has been passed, but if multiple periodic timers become ready
1087during the same loop iteration then order of execution is undefined. 1087during the same loop iteration then order of execution is undefined.
1088 1088
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1095Lots of arguments, lets sort it out... There are basically three modes of 1095Lots of arguments, lets sort it out... There are basically three modes of
1096operation, and we will explain them from simplest to complex: 1096operation, and we will explain them from simplest to complex:
1097 1097
1098=over 4 1098=over 4
1099 1099
1100=item * absolute timer (interval = reschedule_cb = 0) 1100=item * absolute timer (at = time, interval = reschedule_cb = 0)
1101 1101
1102In this configuration the watcher triggers an event at the wallclock time 1102In this configuration the watcher triggers an event at the wallclock time
1103C<at> and doesn't repeat. It will not adjust when a time jump occurs, 1103C<at> and doesn't repeat. It will not adjust when a time jump occurs,
1104that is, if it is to be run at January 1st 2011 then it will run when the 1104that is, if it is to be run at January 1st 2011 then it will run when the
1105system time reaches or surpasses this time. 1105system time reaches or surpasses this time.
1106 1106
1107=item * non-repeating interval timer (interval > 0, reschedule_cb = 0) 1107=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1108 1108
1109In this mode the watcher will always be scheduled to time out at the next 1109In this mode the watcher will always be scheduled to time out at the next
1110C<at + N * interval> time (for some integer N) and then repeat, regardless 1110C<at + N * interval> time (for some integer N, which can also be negative)
1111of any time jumps. 1111and then repeat, regardless of any time jumps.
1112 1112
1113This can be used to create timers that do not drift with respect to system 1113This can be used to create timers that do not drift with respect to system
1114time: 1114time:
1115 1115
1116 ev_periodic_set (&periodic, 0., 3600., 0); 1116 ev_periodic_set (&periodic, 0., 3600., 0);
… …
1122 1122
1123Another way to think about it (for the mathematically inclined) is that 1123Another way to think about it (for the mathematically inclined) is that
1124C<ev_periodic> will try to run the callback in this mode at the next possible 1124C<ev_periodic> will try to run the callback in this mode at the next possible
1125time where C<time = at (mod interval)>, regardless of any time jumps. 1125time where C<time = at (mod interval)>, regardless of any time jumps.
1126 1126
1127For numerical stability it is preferable that the C<at> value is near
1128C<ev_now ()> (the current time), but there is no range requirement for
1129this value.
1130
1127=item * manual reschedule mode (reschedule_cb = callback) 1131=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1128 1132
1129In this mode the values for C<interval> and C<at> are both being 1133In this mode the values for C<interval> and C<at> are both being
1130ignored. Instead, each time the periodic watcher gets scheduled, the 1134ignored. Instead, each time the periodic watcher gets scheduled, the
1131reschedule callback will be called with the watcher as first, and the 1135reschedule callback will be called with the watcher as first, and the
1132current time as second argument. 1136current time as second argument.
1133 1137
1134NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, 1138NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1135ever, or make any event loop modifications>. If you need to stop it, 1139ever, or make any event loop modifications>. If you need to stop it,
1136return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by 1140return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1137starting a prepare watcher). 1141starting an C<ev_prepare> watcher, which is legal).
1138 1142
1139Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 1143Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1140ev_tstamp now)>, e.g.: 1144ev_tstamp now)>, e.g.:
1141 1145
1142 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 1146 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
… …
1164 1168
1165Simply stops and restarts the periodic watcher again. This is only useful 1169Simply stops and restarts the periodic watcher again. This is only useful
1166when you changed some parameters or the reschedule callback would return 1170when you changed some parameters or the reschedule callback would return
1167a different time than the last time it was called (e.g. in a crond like 1171a different time than the last time it was called (e.g. in a crond like
1168program when the crontabs have changed). 1172program when the crontabs have changed).
1173
1174=item ev_tstamp offset [read-write]
1175
1176When repeating, this contains the offset value, otherwise this is the
1177absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1178
1179Can be modified any time, but changes only take effect when the periodic
1180timer fires or C<ev_periodic_again> is being called.
1169 1181
1170=item ev_tstamp interval [read-write] 1182=item ev_tstamp interval [read-write]
1171 1183
1172The current interval value. Can be modified any time, but changes only 1184The current interval value. Can be modified any time, but changes only
1173take effect when the periodic timer fires or C<ev_periodic_again> is being 1185take effect when the periodic timer fires or C<ev_periodic_again> is being

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