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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
705C<ev_resume> directly afterwards to resume timer processing. 705C<ev_resume> directly afterwards to resume timer processing.
706 706
707Effectively, 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
708between 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
709will 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
710occured while suspended). 710occurred while suspended).
711 711
712After 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
713given 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>
714without a previous call to C<ev_suspend>. 714without a previous call to C<ev_suspend>.
715 715
792C<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
793C<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.
794 794
795This "unloop state" will be cleared when entering C<ev_loop> again. 795This "unloop state" will be cleared when entering C<ev_loop> again.
796 796
797It 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.
798 798
799=item ev_ref (loop) 799=item ev_ref (loop)
800 800
801=item ev_unref (loop) 801=item ev_unref (loop)
802 802
872usually 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>,
873as this approaches the timing granularity of most systems. Note that if 873as this approaches the timing granularity of most systems. Note that if
874you 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
875parallelity, then this setting will limit your transaction rate (if you 875parallelity, then this setting will limit your transaction rate (if you
876need 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,
877then you can't do more than 100 transations per second). 877then you can't do more than 100 transactions per second).
878 878
879Setting the I<timeout collect interval> can improve the opportunity for 879Setting the I<timeout collect interval> can improve the opportunity for
880saving power, as the program will "bundle" timer callback invocations that 880saving power, as the program will "bundle" timer callback invocations that
881are "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
882times the process sleeps and wakes up again. Another useful technique to 882times the process sleeps and wakes up again. Another useful technique to
1380 1380
1381For example, to emulate how many other event libraries handle priorities, 1381For example, to emulate how many other event libraries handle priorities,
1382you 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
1383the normal watcher callback, you just start the idle watcher. The real 1383the normal watcher callback, you just start the idle watcher. The real
1384processing is done in the idle watcher callback. This causes libev to 1384processing is done in the idle watcher callback. This causes libev to
1385continously poll and process kernel event data for the watcher, but when 1385continuously poll and process kernel event data for the watcher, but when
1386the 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
1387workable. 1387workable.
1388 1388
1389Usually, however, the lock-out model implemented that way will perform 1389Usually, however, the lock-out model implemented that way will perform
1390miserably 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,
1468 1468
1469If 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
1470known-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
1471C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file 1471C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1472descriptors for which non-blocking operation makes no sense (such as 1472descriptors for which non-blocking operation makes no sense (such as
1473files) - libev doesn't guarentee any specific behaviour in that case. 1473files) - libev doesn't guarantee any specific behaviour in that case.
1474 1474
1475Another 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
1476receive "spurious" readiness notifications, that is your callback might 1476receive "spurious" readiness notifications, that is your callback might
1477be 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
1478because 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
1737 ev_tstamp timeout = last_activity + 60.; 1737 ev_tstamp timeout = last_activity + 60.;
1738 1738
1739 // 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
1740 if (timeout < now) 1740 if (timeout < now)
1741 { 1741 {
1742 // timeout occured, take action 1742 // timeout occurred, take action
1743 } 1743 }
1744 else 1744 else
1745 { 1745 {
1746 // callback was invoked, but there was some activity, re-arm 1746 // callback was invoked, but there was some activity, re-arm
1747 // the watcher to fire in last_activity + 60, which is 1747 // the watcher to fire in last_activity + 60, which is
3342 ev::io iow; 3342 ev::io iow;
3343 iow.set <myclass, &myclass::io_cb> (&obj); 3343 iow.set <myclass, &myclass::io_cb> (&obj);
3344 3344
3345=item w->set (object *) 3345=item w->set (object *)
3346 3346
3347This is an B<experimental> feature that might go away in a future version.
3348
3349This 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
3350will 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
3351functor objects without having to manually specify the C<operator ()> all 3349functor objects without having to manually specify the C<operator ()> all
3352the time. Incidentally, you can then also leave out the template argument 3350the time. Incidentally, you can then also leave out the template argument
3353list. 3351list.
3887EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, 3885EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
3888EV_ASYNC_ENABLE, EV_CHILD_ENABLE. 3886EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3889 3887
3890If undefined or defined to be C<1> (and the platform supports it), then 3888If undefined or defined to be C<1> (and the platform supports it), then
3891the respective watcher type is supported. If defined to be C<0>, then it 3889the respective watcher type is supported. If defined to be C<0>, then it
3892is not. Disabling watcher types mainly saves codesize. 3890is not. Disabling watcher types mainly saves code size.
3893 3891
3894=item EV_FEATURES 3892=item EV_FEATURES
3895 3893
3896If you need to shave off some kilobytes of code at the expense of some 3894If you need to shave off some kilobytes of code at the expense of some
3897speed (but with the full API), you can define this symbol to request 3895speed (but with the full API), you can define this symbol to request
3917 3915
3918=item C<1> - faster/larger code 3916=item C<1> - faster/larger code
3919 3917
3920Use larger code to speed up some operations. 3918Use larger code to speed up some operations.
3921 3919
3922Currently this is used to override some inlining decisions (enlarging the roughly 3920Currently this is used to override some inlining decisions (enlarging the
392330% code size on amd64. 3921code size by roughly 30% on amd64).
3924 3922
3925When optimising for size, use of compiler flags such as C<-Os> with 3923When optimising for size, use of compiler flags such as C<-Os> with
3926gcc recommended, as well as C<-DNDEBUG>, as libev contains a number of 3924gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
3927assertions. 3925assertions.
3928 3926
3929=item C<2> - faster/larger data structures 3927=item C<2> - faster/larger data structures
3930 3928
3931Replaces the small 2-heap for timer management by a faster 4-heap, larger 3929Replaces the small 2-heap for timer management by a faster 4-heap, larger
3932hash table sizes and so on. This will usually further increase codesize 3930hash table sizes and so on. This will usually further increase code size
3933and can additionally have an effect on the size of data structures at 3931and can additionally have an effect on the size of data structures at
3934runtime. 3932runtime.
3935 3933
3936=item C<4> - full API configuration 3934=item C<4> - full API configuration
3937 3935
3974I/O watcher then might come out at only 5Kb. 3972I/O watcher then might come out at only 5Kb.
3975 3973
3976=item EV_AVOID_STDIO 3974=item EV_AVOID_STDIO
3977 3975
3978If this is set to C<1> at compiletime, then libev will avoid using stdio 3976If this is set to C<1> at compiletime, then libev will avoid using stdio
3979functions (printf, scanf, perror etc.). This will increase the codesize 3977functions (printf, scanf, perror etc.). This will increase the code size
3980somewhat, but if your program doesn't otherwise depend on stdio and your 3978somewhat, but if your program doesn't otherwise depend on stdio and your
3981libc allows it, this avoids linking in the stdio library which is quite 3979libc allows it, this avoids linking in the stdio library which is quite
3982big. 3980big.
3983 3981
3984Note that error messages might become less precise when this option is 3982Note that error messages might become less precise when this option is
3988 3986
3989The highest supported signal number, +1 (or, the number of 3987The highest supported signal number, +1 (or, the number of
3990signals): Normally, libev tries to deduce the maximum number of signals 3988signals): Normally, libev tries to deduce the maximum number of signals
3991automatically, but sometimes this fails, in which case it can be 3989automatically, but sometimes this fails, in which case it can be
3992specified. Also, using a lower number than detected (C<32> should be 3990specified. Also, using a lower number than detected (C<32> should be
3993good 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
3994statically allocates some 12-24 bytes per signal number. 3992statically allocates some 12-24 bytes per signal number.
3995 3993
3996=item EV_PID_HASHSIZE 3994=item EV_PID_HASHSIZE
3997 3995
3998C<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
4044will be C<0>. 4042will be C<0>.
4045 4043
4046=item EV_COMMON 4044=item EV_COMMON
4047 4045
4048By default, all watchers have a C<void *data> member. By redefining 4046By default, all watchers have a C<void *data> member. By redefining
4049this macro to a something else you can include more and other types of 4047this macro to something else you can include more and other types of
4050members. You have to define it each time you include one of the files, 4048members. You have to define it each time you include one of the files,
4051though, and it must be identical each time. 4049though, and it must be identical each time.
4052 4050
4053For example, the perl EV module uses something like this: 4051For example, the perl EV module uses something like this:
4054 4052
4353maintainable. 4351maintainable.
4354 4352
4355And of course, some compiler warnings are just plain stupid, or simply 4353And of course, some compiler warnings are just plain stupid, or simply
4356wrong (because they don't actually warn about the condition their message 4354wrong (because they don't actually warn about the condition their message
4357seems to warn about). For example, certain older gcc versions had some 4355seems to warn about). For example, certain older gcc versions had some
4358warnings that resulted an extreme number of false positives. These have 4356warnings that resulted in an extreme number of false positives. These have
4359been fixed, but some people still insist on making code warn-free with 4357been fixed, but some people still insist on making code warn-free with
4360such buggy versions. 4358such buggy versions.
4361 4359
4362While libev is written to generate as few warnings as possible, 4360While libev is written to generate as few warnings as possible,
4363"warn-free" code is not a goal, and it is recommended not to build libev 4361"warn-free" code is not a goal, and it is recommended not to build libev
4653 4651
4654This is a simple rename - all other watcher types use their name 4652This is a simple rename - all other watcher types use their name
4655as revents flag, and now C<ev_timer> does, too. 4653as revents flag, and now C<ev_timer> does, too.
4656 4654
4657Both 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
4658and 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
4659documentation change. 4657documentation change.
4660 4658
4661=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES> 4659=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4662 4660
4663The 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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