--- AnyEvent/lib/AnyEvent.pm 2008/04/24 08:38:13 1.59 +++ AnyEvent/lib/AnyEvent.pm 2008/04/26 04:19:52 1.93 @@ -2,7 +2,7 @@ AnyEvent - provide framework for multiple event loops -EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt - various supported event loops +EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops =head1 SYNOPSIS @@ -80,11 +80,12 @@ module. During the first call of any watcher-creation method, the module tries -to detect the currently loaded event loop by probing whether one of -the following modules is already loaded: L, L, -L, L, L, L, L, L. The first one -found is used. If none are found, the module tries to load these modules -(excluding Event::Lib and Qt) in the order given. The first one that can +to detect the currently loaded event loop by probing whether one of the +following modules is already loaded: L, L, L, +L, L, L, L, L, L, +L. The first one found is used. If none are found, the module tries +to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl +adaptor should always succeed) in the order given. The first one that can be successfully loaded will be used. If, after this, still none could be found, AnyEvent will fall back to a pure-perl event loop, which is not very efficient, but should work everywhere. @@ -137,22 +138,24 @@ my variables are only visible after the statement in which they are declared. -=head2 IO WATCHERS +=head2 I/O WATCHERS You can create an I/O watcher by calling the C<< AnyEvent->io >> method with the following mandatory key-value pairs as arguments: -C the Perl I (I file descriptor) to watch for -events. C must be a string that is either C or C, which -creates a watcher waiting for "r"eadable or "w"ritable events, +C the Perl I (I file descriptor) to watch +for events. C must be a string that is either C or C, +which creates a watcher waiting for "r"eadable or "w"ritable events, respectively. C is the callback to invoke each time the file handle becomes ready. -As long as the I/O watcher exists it will keep the file descriptor or a -copy of it alive/open. - -It is not allowed to close a file handle as long as any watcher is active -on the underlying file descriptor. +Although the callback might get passed parameters, their value and +presence is undefined and you cannot rely on them. Portable AnyEvent +callbacks cannot use arguments passed to I/O watcher callbacks. + +The I/O watcher might use the underlying file descriptor or a copy of it. +You must not close a file handle as long as any watcher is active on the +underlying file descriptor. Some event loops issue spurious readyness notifications, so you should always use non-blocking calls when reading/writing from/to your file @@ -173,8 +176,12 @@ method with the following mandatory arguments: C specifies after how many seconds (fractional values are -supported) should the timer activate. C the callback to invoke in that -case. +supported) the callback should be invoked. C is the callback to invoke +in that case. + +Although the callback might get passed parameters, their value and +presence is undefined and you cannot rely on them. Portable AnyEvent +callbacks cannot use arguments passed to time watcher callbacks. The timer callback will be invoked at most once: if you want a repeating timer you have to create a new watcher (this is a limitation by both Tk @@ -229,6 +236,10 @@ I without any C prefix, C is the Perl callback to be invoked whenever a signal occurs. +Although the callback might get passed parameters, their value and +presence is undefined and you cannot rely on them. Portable AnyEvent +callbacks cannot use arguments passed to signal watcher callbacks. + Multiple signal occurances can be clumped together into one callback invocation, and callback invocation will be synchronous. synchronous means that it might take a while until the signal gets handled by the process, @@ -252,18 +263,41 @@ watches for any child process exit). The watcher will trigger as often as status change for the child are received. This works by installing a signal handler for C. The callback will be called with the pid -and exit status (as returned by waitpid). +and exit status (as returned by waitpid), so unlike other watcher types, +you I rely on child watcher callback arguments. + +There is a slight catch to child watchers, however: you usually start them +I the child process was created, and this means the process could +have exited already (and no SIGCHLD will be sent anymore). + +Not all event models handle this correctly (POE doesn't), but even for +event models that I handle this correctly, they usually need to be +loaded before the process exits (i.e. before you fork in the first place). -Example: wait for pid 1333 +This means you cannot create a child watcher as the very first thing in an +AnyEvent program, you I to create at least one watcher before you +C the child (alternatively, you can call C). + +Example: fork a process and wait for it + + my $done = AnyEvent->condvar; + + AnyEvent::detect; # force event module to be initialised + + my $pid = fork or exit 5; my $w = AnyEvent->child ( - pid => 1333, + pid => $pid, cb => sub { my ($pid, $status) = @_; warn "pid $pid exited with status $status"; + $done->broadcast; }, ); + # do something else, then wait for process exit + $done->wait; + =head2 CONDITION VARIABLES Condition variables can be created by calling the C<< AnyEvent->condvar >> @@ -360,10 +394,21 @@ AnyEvent::Impl::EV based on EV (an interface to libev, best choice). AnyEvent::Impl::Event based on Event, second best choice. AnyEvent::Impl::Glib based on Glib, third-best choice. - AnyEvent::Impl::Tk based on Tk, very bad choice. AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. + AnyEvent::Impl::Tk based on Tk, very bad choice. AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. + AnyEvent::Impl::POE based on POE, not generic enough for full support. + +There is no support for WxWidgets, as WxWidgets has no support for +watching file handles. However, you can use WxWidgets through the +POE Adaptor, as POE has a Wx backend that simply polls 20 times per +second, which was considered to be too horrible to even consider for +AnyEvent. Likewise, other POE backends can be used by AnyEvent by using +it's adaptor. + +AnyEvent knows about L and L and will try to use L when +autodetecting them. =item AnyEvent::detect @@ -424,7 +469,7 @@ use Carp; -our $VERSION = '3.2'; +our $VERSION = '3.3'; our $MODEL; our $AUTOLOAD; @@ -441,11 +486,13 @@ [Event:: => AnyEvent::Impl::Event::], [Glib:: => AnyEvent::Impl::Glib::], [Tk:: => AnyEvent::Impl::Tk::], + [Wx:: => AnyEvent::Impl::POE::], + [Prima:: => AnyEvent::Impl::POE::], [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], -); -my @models_detect = ( - [Qt:: => AnyEvent::Impl::Qt::], # requires special main program + # everything below here will not be autoprobed as the pureperl backend should work everywhere [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy + [Qt:: => AnyEvent::Impl::Qt::], # requires special main program + [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza ); our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY); @@ -459,12 +506,14 @@ if (eval "require $model") { $MODEL = $model; warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1; + } else { + warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose; } } # check for already loaded models unless ($MODEL) { - for (@REGISTRY, @models, @models_detect) { + for (@REGISTRY, @models) { my ($package, $model) = @$_; if (${"$package\::VERSION"} > 0) { if (eval "require $model") { @@ -661,6 +710,14 @@ =item C +By default, AnyEvent will be completely silent except in fatal +conditions. You can set this environment variable to make AnyEvent more +talkative. + +When set to C<1> or higher, causes AnyEvent to warn about unexpected +conditions, such as not being able to load the event model specified by +C. + When set to C<2> or higher, cause AnyEvent to report to STDERR which event model it chooses. @@ -684,7 +741,7 @@ =head1 EXAMPLE PROGRAM -The following program uses an IO watcher to read data from STDIN, a timer +The following program uses an I/O watcher to read data from STDIN, a timer to display a message once per second, and a condition variable to quit the program when the user enters quit: @@ -838,6 +895,260 @@ $quit->wait; + +=head1 BENCHMARKS + +To give you an idea of the performance and overheads that AnyEvent adds +over the event loops themselves and to give you an impression of the speed +of various event loops I prepared some benchmarks. + +=head2 BENCHMARKING ANYEVENT OVERHEAD + +Here is a benchmark of various supported event models used natively and +through anyevent. The benchmark creates a lot of timers (with a zero +timeout) and I/O watchers (watching STDOUT, a pty, to become writable, +which it is), lets them fire exactly once and destroys them again. + +Source code for this benchmark is found as F in the AnyEvent +distribution. + +=head3 Explanation of the columns + +I is the number of event watchers created/destroyed. Since +different event models feature vastly different performances, each event +loop was given a number of watchers so that overall runtime is acceptable +and similar between tested event loop (and keep them from crashing): Glib +would probably take thousands of years if asked to process the same number +of watchers as EV in this benchmark. + +I is the number of bytes (as measured by the resident set size, +RSS) consumed by each watcher. This method of measuring captures both C +and Perl-based overheads. + +I is the time, in microseconds (millionths of seconds), that it +takes to create a single watcher. The callback is a closure shared between +all watchers, to avoid adding memory overhead. That means closure creation +and memory usage is not included in the figures. + +I is the time, in microseconds, used to invoke a simple +callback. The callback simply counts down a Perl variable and after it was +invoked "watcher" times, it would C<< ->broadcast >> a condvar once to +signal the end of this phase. + +I is the time, in microseconds, that it takes to destroy a single +watcher. + +=head3 Results + + name watchers bytes create invoke destroy comment + EV/EV 400000 244 0.56 0.46 0.31 EV native interface + EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers + CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal + Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation + Event/Event 16000 516 31.88 31.30 0.85 Event native interface + Event/Any 16000 936 39.17 33.63 1.43 Event + AnyEvent watchers + Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour + Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers + POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event + POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select + +=head3 Discussion + +The benchmark does I measure scalability of the event loop very +well. For example, a select-based event loop (such as the pure perl one) +can never compete with an event loop that uses epoll when the number of +file descriptors grows high. In this benchmark, all events become ready at +the same time, so select/poll-based implementations get an unnatural speed +boost. + +C is the sole leader regarding speed and memory use, which are both +maximal/minimal, respectively. Even when going through AnyEvent, it uses +far less memory than any other event loop and is still faster than Event +natively. + +The pure perl implementation is hit in a few sweet spots (both the +constant timeout and the use of a single fd hit optimisations in the perl +interpreter and the backend itself). Nevertheless this shows that it +adds very little overhead in itself. Like any select-based backend its +performance becomes really bad with lots of file descriptors (and few of +them active), of course, but this was not subject of this benchmark. + +The C module has a relatively high setup and callback invocation +cost, but overall scores in on the third place. + +C's memory usage is quite a bit higher, but it features a +faster callback invocation and overall ends up in the same class as +C. However, Glib scales extremely badly, doubling the number of +watchers increases the processing time by more than a factor of four, +making it completely unusable when using larger numbers of watchers +(note that only a single file descriptor was used in the benchmark, so +inefficiencies of C do not account for this). + +The C adaptor works relatively well. The fact that it crashes with +more than 2000 watchers is a big setback, however, as correctness takes +precedence over speed. Nevertheless, its performance is surprising, as the +file descriptor is dup()ed for each watcher. This shows that the dup() +employed by some adaptors is not a big performance issue (it does incur a +hidden memory cost inside the kernel which is not reflected in the figures +above). + +C, regardless of underlying event loop (whether using its pure +perl select-based backend or the Event module, the POE-EV backend +couldn't be tested because it wasn't working) shows abysmal performance +and memory usage: Watchers use almost 30 times as much memory as +EV watchers, and 10 times as much memory as Event (the high memory +requirements are caused by requiring a session for each watcher). Watcher +invocation speed is almost 900 times slower than with AnyEvent's pure perl +implementation. The design of the POE adaptor class in AnyEvent can not +really account for this, as session creation overhead is small compared +to execution of the state machine, which is coded pretty optimally within +L. POE simply seems to be abysmally slow. + +=head3 Summary + +=over 4 + +=item * Using EV through AnyEvent is faster than any other event loop +(even when used without AnyEvent), but most event loops have acceptable +performance with or without AnyEvent. + +=item * The overhead AnyEvent adds is usually much smaller than the overhead of +the actual event loop, only with extremely fast event loops such as EV +adds AnyEvent significant overhead. + +=item * You should avoid POE like the plague if you want performance or +reasonable memory usage. + +=back + +=head2 BENCHMARKING THE LARGE SERVER CASE + +This benchmark atcually benchmarks the event loop itself. It works by +creating a number of "servers": each server consists of a socketpair, a +timeout watcher that gets reset on activity (but never fires), and an I/O +watcher waiting for input on one side of the socket. Each time the socket +watcher reads a byte it will write that byte to a random other "server". + +The effect is that there will be a lot of I/O watchers, only part of which +are active at any one point (so there is a constant number of active +fds for each loop iterstaion, but which fds these are is random). The +timeout is reset each time something is read because that reflects how +most timeouts work (and puts extra pressure on the event loops). + +In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100 +(1%) are active. This mirrors the activity of large servers with many +connections, most of which are idle at any one point in time. + +Source code for this benchmark is found as F in the AnyEvent +distribution. + +=head3 Explanation of the columns + +I is the number of sockets, and twice the number of "servers" (as +eahc server has a read and write socket end). + +I is the time it takes to create a socketpair (which is +nontrivial) and two watchers: an I/O watcher and a timeout watcher. + +I, the most important value, is the time it takes to handle a +single "request", that is, reading the token from the pipe and forwarding +it to another server. This includes deleting the old timeout and creating +a new one that moves the timeout into the future. + +=head3 Results + + name sockets create request + EV 20000 69.01 11.16 + Perl 20000 75.28 112.76 + Event 20000 212.62 257.32 + Glib 20000 651.16 1896.30 + POE 20000 349.67 12317.24 uses POE::Loop::Event + +=head3 Discussion + +This benchmark I measure scalability and overall performance of the +particular event loop. + +EV is again fastest. Since it is using epoll on my system, the setup time +is relatively high, though. + +Perl surprisingly comes second. It is much faster than the C-based event +loops Event and Glib. + +Event suffers from high setup time as well (look at its code and you will +understand why). Callback invocation also has a high overhead compared to +the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event +uses select or poll in basically all documented configurations. + +Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It +clearly fails to perform with many filehandles or in busy servers. + +POE is still completely out of the picture, taking over 1000 times as long +as EV, and over 100 times as long as the Perl implementation, even though +it uses a C-based event loop in this case. + +=head3 Summary + +=over 4 + +=item * The pure perl implementation performs extremely well, considering +that it uses select. + +=item * Avoid Glib or POE in large projects where performance matters. + +=back + +=head2 BENCHMARKING SMALL SERVERS + +While event loops should scale (and select-based ones do not...) even to +large servers, most programs we (or I :) actually write have only a few +I/O watchers. + +In this benchmark, I use the same benchmark program as in the large server +case, but it uses only eight "servers", of which three are active at any +one time. This should reflect performance for a small server relatively +well. + +The columns are identical to the previous table. + +=head3 Results + + name sockets create request + EV 16 20.00 6.54 + Event 16 81.27 35.86 + Glib 16 32.63 15.48 + Perl 16 24.62 162.37 + POE 16 261.87 276.28 uses POE::Loop::Event + +=head3 Discussion + +The benchmark tries to test the performance of a typical small +server. While knowing how various event loops perform is interesting, keep +in mind that their overhead in this case is usually not as important, due +to the small absolute number of watchers. + +EV is again fastest. + +The C-based event loops Event and Glib come in second this time, as the +overhead of running an iteration is much smaller in C than in Perl (little +code to execute in the inner loop, and perl's function calling overhead is +high, and updating all the data structures is costly). + +The pure perl event loop is much slower, but still competitive. + +POE also performs much better in this case, but is is stillf ar behind the +others. + +=head3 Summary + +=over 4 + +=item * C-based event loops perform very well with small number of +watchers, as the management overhead dominates. + +=back + + =head1 FORK Most event libraries are not fork-safe. The ones who are usually are @@ -846,6 +1157,7 @@ If you have to fork, you must either do so I creating your first watcher OR you must not use AnyEvent at all in the child. + =head1 SECURITY CONSIDERATIONS AnyEvent can be forced to load any event model via @@ -862,19 +1174,21 @@ use AnyEvent; + =head1 SEE ALSO Event modules: L, L, L, L, L, L, L, L, L, L, -L, L. +L, L, L. Implementations: L, L, L, L, L, L, L, L, -L. +L, L. Nontrivial usage examples: L, L. + =head1 AUTHOR Marc Lehmann