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Revision 1.292 by sf-exg, Mon Mar 22 09:57:01 2010 UTC vs.
Revision 1.298 by sf-exg, Sat Jul 31 23:00:11 2010 UTC

75While this document tries to be as complete as possible in documenting 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 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 77on event-based programming, nor will it introduce event-based programming
78with libev. 78with libev.
79 79
80Familarity with event based programming techniques in general is assumed 80Familiarity with event based programming techniques in general is assumed
81throughout this document. 81throughout this document.
82 82
83=head1 ABOUT LIBEV 83=head1 ABOUT LIBEV
84 84
85Libev 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
124this argument. 124this argument.
125 125
126=head2 TIME REPRESENTATION 126=head2 TIME REPRESENTATION
127 127
128Libev represents time as a single floating point number, representing 128Libev represents time as a single floating point number, representing
129the (fractional) number of seconds since the (POSIX) epoch (somewhere 129the (fractional) number of seconds since the (POSIX) epoch (in practise
130near the beginning of 1970, details are complicated, don't ask). This 130somewhere near the beginning of 1970, details are complicated, don't
131type is called C<ev_tstamp>, which is what you should use too. It usually 131ask). This type is called C<ev_tstamp>, which is what you should use
132aliases to the C<double> type in C. When you need to do any calculations 132too. It usually aliases to the C<double> type in C. When you need to do
133on it, you should treat it as some floating point value. Unlike the name 133any calculations on it, you should treat it as some floating point value.
134
134component C<stamp> might indicate, it is also used for time differences 135Unlike the name component C<stamp> might indicate, it is also used for
135throughout libev. 136time differences (e.g. delays) throughout libev.
136 137
137=head1 ERROR HANDLING 138=head1 ERROR HANDLING
138 139
139Libev knows three classes of errors: operating system errors, usage errors 140Libev knows three classes of errors: operating system errors, usage errors
140and internal errors (bugs). 141and internal errors (bugs).
191as this indicates an incompatible change. Minor versions are usually 192as this indicates an incompatible change. Minor versions are usually
192compatible to older versions, so a larger minor version alone is usually 193compatible to older versions, so a larger minor version alone is usually
193not a problem. 194not a problem.
194 195
195Example: Make sure we haven't accidentally been linked against the wrong 196Example: Make sure we haven't accidentally been linked against the wrong
196version. 197version (note, however, that this will not detect ABI mismatches :).
197 198
198 assert (("libev version mismatch", 199 assert (("libev version mismatch",
199 ev_version_major () == EV_VERSION_MAJOR 200 ev_version_major () == EV_VERSION_MAJOR
200 && ev_version_minor () >= EV_VERSION_MINOR)); 201 && ev_version_minor () >= EV_VERSION_MINOR));
201 202
704C<ev_resume> directly afterwards to resume timer processing. 705C<ev_resume> directly afterwards to resume timer processing.
705 706
706Effectively, all C<ev_timer> watchers will be delayed by the time spend 707Effectively, all C<ev_timer> watchers will be delayed by the time spend
707between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers 708between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
708will be rescheduled (that is, they will lose any events that would have 709will be rescheduled (that is, they will lose any events that would have
709occured while suspended). 710occurred while suspended).
710 711
711After calling C<ev_suspend> you B<must not> call I<any> function on the 712After calling C<ev_suspend> you B<must not> call I<any> function on the
712given loop other than C<ev_resume>, and you B<must not> call C<ev_resume> 713given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
713without a previous call to C<ev_suspend>. 714without a previous call to C<ev_suspend>.
714 715
791C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or 792C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
792C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. 793C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
793 794
794This "unloop state" will be cleared when entering C<ev_loop> again. 795This "unloop state" will be cleared when entering C<ev_loop> again.
795 796
796It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls. 797It is safe to call C<ev_unloop> from outside any C<ev_loop> calls.
797 798
798=item ev_ref (loop) 799=item ev_ref (loop)
799 800
800=item ev_unref (loop) 801=item ev_unref (loop)
801 802
871usually doesn't make much sense to set it to a lower value than C<0.01>, 872usually doesn't make much sense to set it to a lower value than C<0.01>,
872as this approaches the timing granularity of most systems. Note that if 873as this approaches the timing granularity of most systems. Note that if
873you do transactions with the outside world and you can't increase the 874you do transactions with the outside world and you can't increase the
874parallelity, then this setting will limit your transaction rate (if you 875parallelity, then this setting will limit your transaction rate (if you
875need to poll once per transaction and the I/O collect interval is 0.01, 876need to poll once per transaction and the I/O collect interval is 0.01,
876then you can't do more than 100 transations per second). 877then you can't do more than 100 transactions per second).
877 878
878Setting the I<timeout collect interval> can improve the opportunity for 879Setting the I<timeout collect interval> can improve the opportunity for
879saving power, as the program will "bundle" timer callback invocations that 880saving power, as the program will "bundle" timer callback invocations that
880are "near" in time together, by delaying some, thus reducing the number of 881are "near" in time together, by delaying some, thus reducing the number of
881times the process sleeps and wakes up again. Another useful technique to 882times the process sleeps and wakes up again. Another useful technique to
1379 1380
1380For example, to emulate how many other event libraries handle priorities, 1381For example, to emulate how many other event libraries handle priorities,
1381you can associate an C<ev_idle> watcher to each such watcher, and in 1382you can associate an C<ev_idle> watcher to each such watcher, and in
1382the normal watcher callback, you just start the idle watcher. The real 1383the normal watcher callback, you just start the idle watcher. The real
1383processing is done in the idle watcher callback. This causes libev to 1384processing is done in the idle watcher callback. This causes libev to
1384continously poll and process kernel event data for the watcher, but when 1385continuously poll and process kernel event data for the watcher, but when
1385the lock-out case is known to be rare (which in turn is rare :), this is 1386the lock-out case is known to be rare (which in turn is rare :), this is
1386workable. 1387workable.
1387 1388
1388Usually, however, the lock-out model implemented that way will perform 1389Usually, however, the lock-out model implemented that way will perform
1389miserably under the type of load it was designed to handle. In that case, 1390miserably under the type of load it was designed to handle. In that case,
1403 { 1404 {
1404 // stop the I/O watcher, we received the event, but 1405 // stop the I/O watcher, we received the event, but
1405 // are not yet ready to handle it. 1406 // are not yet ready to handle it.
1406 ev_io_stop (EV_A_ w); 1407 ev_io_stop (EV_A_ w);
1407 1408
1408 // start the idle watcher to ahndle the actual event. 1409 // start the idle watcher to handle the actual event.
1409 // it will not be executed as long as other watchers 1410 // it will not be executed as long as other watchers
1410 // with the default priority are receiving events. 1411 // with the default priority are receiving events.
1411 ev_idle_start (EV_A_ &idle); 1412 ev_idle_start (EV_A_ &idle);
1412 } 1413 }
1413 1414
1467 1468
1468If you cannot use non-blocking mode, then force the use of a 1469If you cannot use non-blocking mode, then force the use of a
1469known-to-be-good backend (at the time of this writing, this includes only 1470known-to-be-good backend (at the time of this writing, this includes only
1470C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file 1471C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1471descriptors for which non-blocking operation makes no sense (such as 1472descriptors for which non-blocking operation makes no sense (such as
1472files) - libev doesn't guarentee any specific behaviour in that case. 1473files) - libev doesn't guarantee any specific behaviour in that case.
1473 1474
1474Another thing you have to watch out for is that it is quite easy to 1475Another thing you have to watch out for is that it is quite easy to
1475receive "spurious" readiness notifications, that is your callback might 1476receive "spurious" readiness notifications, that is your callback might
1476be called with C<EV_READ> but a subsequent C<read>(2) will actually block 1477be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1477because there is no data. Not only are some backends known to create a 1478because there is no data. Not only are some backends known to create a
1736 ev_tstamp timeout = last_activity + 60.; 1737 ev_tstamp timeout = last_activity + 60.;
1737 1738
1738 // if last_activity + 60. is older than now, we did time out 1739 // if last_activity + 60. is older than now, we did time out
1739 if (timeout < now) 1740 if (timeout < now)
1740 { 1741 {
1741 // timeout occured, take action 1742 // timeout occurred, take action
1742 } 1743 }
1743 else 1744 else
1744 { 1745 {
1745 // callback was invoked, but there was some activity, re-arm 1746 // callback was invoked, but there was some activity, re-arm
1746 // the watcher to fire in last_activity + 60, which is 1747 // the watcher to fire in last_activity + 60, which is
1773 callback (loop, timer, EV_TIMER); 1774 callback (loop, timer, EV_TIMER);
1774 1775
1775And when there is some activity, simply store the current time in 1776And when there is some activity, simply store the current time in
1776C<last_activity>, no libev calls at all: 1777C<last_activity>, no libev calls at all:
1777 1778
1778 last_actiivty = ev_now (loop); 1779 last_activity = ev_now (loop);
1779 1780
1780This technique is slightly more complex, but in most cases where the 1781This technique is slightly more complex, but in most cases where the
1781time-out is unlikely to be triggered, much more efficient. 1782time-out is unlikely to be triggered, much more efficient.
1782 1783
1783Changing the timeout is trivial as well (if it isn't hard-coded in the 1784Changing the timeout is trivial as well (if it isn't hard-coded in the
3341 ev::io iow; 3342 ev::io iow;
3342 iow.set <myclass, &myclass::io_cb> (&obj); 3343 iow.set <myclass, &myclass::io_cb> (&obj);
3343 3344
3344=item w->set (object *) 3345=item w->set (object *)
3345 3346
3346This is an B<experimental> feature that might go away in a future version.
3347
3348This is a variation of a method callback - leaving out the method to call 3347This is a variation of a method callback - leaving out the method to call
3349will default the method to C<operator ()>, which makes it possible to use 3348will default the method to C<operator ()>, which makes it possible to use
3350functor objects without having to manually specify the C<operator ()> all 3349functor objects without having to manually specify the C<operator ()> all
3351the time. Incidentally, you can then also leave out the template argument 3350the time. Incidentally, you can then also leave out the template argument
3352list. 3351list.
3987 3986
3988The highest supported signal number, +1 (or, the number of 3987The highest supported signal number, +1 (or, the number of
3989signals): Normally, libev tries to deduce the maximum number of signals 3988signals): Normally, libev tries to deduce the maximum number of signals
3990automatically, but sometimes this fails, in which case it can be 3989automatically, but sometimes this fails, in which case it can be
3991specified. Also, using a lower number than detected (C<32> should be 3990specified. Also, using a lower number than detected (C<32> should be
3992good for about any system in existance) can save some memory, as libev 3991good for about any system in existence) can save some memory, as libev
3993statically allocates some 12-24 bytes per signal number. 3992statically allocates some 12-24 bytes per signal number.
3994 3993
3995=item EV_PID_HASHSIZE 3994=item EV_PID_HASHSIZE
3996 3995
3997C<ev_child> watchers use a small hash table to distribute workload by 3996C<ev_child> watchers use a small hash table to distribute workload by
4652 4651
4653This is a simple rename - all other watcher types use their name 4652This is a simple rename - all other watcher types use their name
4654as revents flag, and now C<ev_timer> does, too. 4653as revents flag, and now C<ev_timer> does, too.
4655 4654
4656Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions 4655Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
4657and continue to be present for the forseeable future, so this is mostly a 4656and continue to be present for the foreseeable future, so this is mostly a
4658documentation change. 4657documentation change.
4659 4658
4660=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES> 4659=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4661 4660
4662The preprocessor symbol C<EV_MINIMAL> has been replaced by a different 4661The preprocessor symbol C<EV_MINIMAL> has been replaced by a different

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