--- AnyEvent/README 2005/12/30 01:28:31 1.4 +++ AnyEvent/README 2008/04/16 15:10:10 1.15 @@ -1,50 +1,69 @@ NAME AnyEvent - provide framework for multiple event loops - Event, Coro, Glib, Tk - various supported event loops + EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported + event loops SYNOPSIS use AnyEvent; - my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub { - my ($poll_got) = @_; + my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... }); - * only one io watcher per $fh and $poll type is allowed (i.e. on a - socket you can have one r + one w or one rw watcher, not any more - (limitation by Tk). - - * the $poll_got passed to the handler needs to be checked by looking for - single characters (e.g. with a regex), as it can contain more event - types than were requested (e.g. a 'w' watcher might generate 'rw' - events, limitation by Glib). - - * AnyEvent will keep filehandles alive, so as long as the watcher - exists, the filehandle exists. - my $w = AnyEvent->timer (after => $seconds, cb => sub { ... }); - * io and time watchers get canceled whenever $w is destroyed, so keep a - copy - - * timers can only be used once and must be recreated for repeated - operation (limitation by Glib and Tk). - - my $w = AnyEvent->condvar; # kind of main loop replacement - $w->wait; # enters main loop till $condvar gets ->broadcast + my $w = AnyEvent->condvar; # stores wether a condition was flagged + $w->wait; # enters "main loop" till $condvar gets ->broadcast $w->broadcast; # wake up current and all future wait's - * condvars are used to give blocking behaviour when neccessary. Create a - condvar for any "request" or "event" your module might create, - "->broadcast" it when the event happens and provide a function that - calls "->wait" for it. See the examples below. +WHY YOU SHOULD USE THIS MODULE (OR NOT) + Glib, POE, IO::Async, Event... CPAN offers event models by the dozen + nowadays. So what is different about AnyEvent? + + Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of + policy* and AnyEvent is *small and efficient*. + + First and foremost, *AnyEvent is not an event model* itself, it only + interfaces to whatever event model the main program happens to use in a + pragmatic way. For event models and certain classes of immortals alike, + the statement "there can only be one" is a bitter reality, and AnyEvent + helps hiding the differences. + + The goal of AnyEvent is to offer module authors the ability to do event + programming (waiting for I/O or timer events) without subscribing to a + religion, a way of living, and most importantly: without forcing your + module users into the same thing by forcing them to use the same event + model you use. + + For modules like POE or IO::Async (which is actually doing all I/O + *synchronously*...), using them in your module is like joining a cult: + After you joined, you are dependent on them and you cannot use anything + else, as it is simply incompatible to everything that isn't itself. + + AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk + works fine etc. etc. but none of these work together with the rest: POE + + IO::Async? no go. Tk + Event? no go. If your module uses one of those, + every user of your module has to use it, too. If your module uses + AnyEvent, it works transparently with all event models it supports + (including stuff like POE and IO::Async). + + In addition of being free of having to use *the one and only true event + model*, AnyEvent also is free of bloat and policy: with POE or similar + modules, you get an enourmous amount of code and strict rules you have + to follow. AnyEvent, on the other hand, is lean and to the point by only + offering the functionality that is useful, in as thin as a wrapper as + technically possible. + + Of course, if you want lots of policy (this can arguably be somewhat + useful) and you want to force your users to use the one and only event + model, you should *not* use this module. DESCRIPTION AnyEvent provides an identical interface to multiple event loops. This - allows module authors to utilizy an event loop without forcing module + allows module authors to utilise an event loop without forcing module users to use the same event loop (as only a single event loop can coexist peacefully at any one time). @@ -53,10 +72,243 @@ On the first call of any method, the module tries to detect the currently loaded event loop by probing wether any of the following - modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is - used. If none is found, the module tries to load these modules in the - order given. The first one that could be successfully loaded will be - used. If still none could be found, it will issue an error. + modules is loaded: Coro::EV, Coro::Event, EV, Event, Glib, Tk. The first + one found is used. If none are found, the module tries to load these + modules in the order given. The first one that could be successfully + loaded will be used. If still none could be found, AnyEvent will fall + back to a pure-perl event loop, which is also not very efficient. + + Because AnyEvent first checks for modules that are already loaded, + loading an Event model explicitly before first using AnyEvent will + likely make that model the default. For example: + + use Tk; + use AnyEvent; + + # .. AnyEvent will likely default to Tk + + The pure-perl implementation of AnyEvent is called + "AnyEvent::Impl::Perl". Like other event modules you can load it + explicitly. + +WATCHERS + AnyEvent has the central concept of a *watcher*, which is an object that + stores relevant data for each kind of event you are waiting for, such as + the callback to call, the filehandle to watch, etc. + + These watchers are normal Perl objects with normal Perl lifetime. After + creating a watcher it will immediately "watch" for events and invoke the + callback. To disable the watcher you have to destroy it (e.g. by setting + the variable that stores it to "undef" or otherwise deleting all + references to it). + + All watchers are created by calling a method on the "AnyEvent" class. + + IO WATCHERS + You can create I/O watcher by calling the "AnyEvent->io" method with the + following mandatory arguments: + + "fh" the Perl *filehandle* (not filedescriptor) to watch for events. + "poll" must be a string that is either "r" or "w", that creates a + watcher waiting for "r"eadable or "w"ritable events. "cb" the callback + to invoke everytime the filehandle becomes ready. + + Filehandles will be kept alive, so as long as the watcher exists, the + filehandle exists, too. + + Example: + + # wait for readability of STDIN, then read a line and disable the watcher + my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { + chomp (my $input = ); + warn "read: $input\n"; + undef $w; + }); + + TIME WATCHERS + You can create a time watcher by calling the "AnyEvent->timer" method + with the following mandatory arguments: + + "after" after how many seconds (fractions are supported) should the + timer activate. "cb" the callback to invoke. + + 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 + and Glib). + + Example: + + # fire an event after 7.7 seconds + my $w = AnyEvent->timer (after => 7.7, cb => sub { + warn "timeout\n"; + }); + + # to cancel the timer: + undef $w; + + CONDITION WATCHERS + Condition watchers can be created by calling the "AnyEvent->condvar" + method without any arguments. + + A condition watcher watches for a condition - precisely that the + "->broadcast" method has been called. + + Note that condition watchers recurse into the event loop - if you have + two watchers that call "->wait" in a round-robbin fashion, you lose. + Therefore, condition watchers are good to export to your caller, but you + should avoid making a blocking wait, at least in callbacks, as this + usually asks for trouble. + + The watcher has only two methods: + + $cv->wait + Wait (blocking if necessary) until the "->broadcast" method has been + called on c<$cv>, while servicing other watchers normally. + + You can only wait once on a condition - additional calls will return + immediately. + + Not all event models support a blocking wait - some die in that case + (programs might want to do that so they stay interactive), so *if + you are using this from a module, never require a blocking wait*, + but let the caller decide wether the call will block or not (for + example, by coupling condition variables with some kind of request + results and supporting callbacks so the caller knows that getting + the result will not block, while still suppporting blocking waits if + the caller so desires). + + Another reason *never* to "->wait" in a module is that you cannot + sensibly have two "->wait"'s in parallel, as that would require + multiple interpreters or coroutines/threads, none of which + "AnyEvent" can supply (the coroutine-aware backends "Coro::EV" and + "Coro::Event" explicitly support concurrent "->wait"'s from + different coroutines, however). + + $cv->broadcast + Flag the condition as ready - a running "->wait" and all further + calls to "wait" will return after this method has been called. If + nobody is waiting the broadcast will be remembered.. + + Example: + + # wait till the result is ready + my $result_ready = AnyEvent->condvar; + + # do something such as adding a timer + # or socket watcher the calls $result_ready->broadcast + # when the "result" is ready. + + $result_ready->wait; + + SIGNAL WATCHERS + You can listen for signals using a signal watcher, "signal" is the + signal *name* without any "SIG" prefix. Multiple signals events can be + clumped together into one callback invocation, and callback invocation + might or might not be asynchronous. + + These watchers might use %SIG, so programs overwriting those signals + directly will likely not work correctly. + + Example: exit on SIGINT + + my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); + + CHILD PROCESS WATCHERS + You can also listen for the status of a child process specified by the + "pid" argument (or any child if the pid argument is 0). The watcher will + trigger as often as status change for the child are received. This works + by installing a signal handler for "SIGCHLD". The callback will be + called with the pid and exit status (as returned by waitpid). + + Example: wait for pid 1333 + + my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); + +GLOBALS + $AnyEvent::MODEL + Contains "undef" until the first watcher is being created. Then it + contains the event model that is being used, which is the name of + the Perl class implementing the model. This class is usually one of + the "AnyEvent::Impl:xxx" modules, but can be any other class in the + case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). + + The known classes so far are: + + AnyEvent::Impl::CoroEV based on Coro::EV, best choice. + AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. + AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). + AnyEvent::Impl::Event based on Event, also 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::detect + Returns $AnyEvent::MODEL, forcing autodetection of the event model + if necessary. You should only call this function right before you + would have created an AnyEvent watcher anyway, that is, very late at + runtime. + +WHAT TO DO IN A MODULE + As a module author, you should "use AnyEvent" and call AnyEvent methods + freely, but you should not load a specific event module or rely on it. + + Be careful when you create watchers in the module body - Anyevent will + decide which event module to use as soon as the first method is called, + so by calling AnyEvent in your module body you force the user of your + module to load the event module first. + +WHAT TO DO IN THE MAIN PROGRAM + There will always be a single main program - the only place that should + dictate which event model to use. + + If it doesn't care, it can just "use AnyEvent" and use it itself, or not + do anything special and let AnyEvent decide which implementation to + chose. + + If the main program relies on a specific event model (for example, in + Gtk2 programs you have to rely on either Glib or Glib::Event), you + should load it before loading AnyEvent or any module that uses it, + generally, as early as possible. The reason is that modules might create + watchers when they are loaded, and AnyEvent will decide on the event + model to use as soon as it creates watchers, and it might chose the + wrong one unless you load the correct one yourself. + + You can chose to use a rather inefficient pure-perl implementation by + loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is + generally better. + +SUPPLYING YOUR OWN EVENT MODEL INTERFACE + If you need to support another event library which isn't directly + supported by AnyEvent, you can supply your own interface to it by + pushing, before the first watcher gets created, the package name of the + event module and the package name of the interface to use onto + @AnyEvent::REGISTRY. You can do that before and even without loading + AnyEvent. + + Example: + + push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; + + This tells AnyEvent to (literally) use the "urxvt::anyevent::" + package/class when it finds the "urxvt" package/module is loaded. When + AnyEvent is loaded and asked to find a suitable event model, it will + first check for the presence of urxvt. + + The class should provide implementations for all watcher types (see + AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code) + and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to + see the sources). + + The above isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) uses the + above line as-is. An interface isn't included in AnyEvent because it + doesn't make sense outside the embedded interpreter inside + *rxvt-unicode*, and it is updated and maintained as part of the + *rxvt-unicode* distribution. + + *rxvt-unicode* also cheats a bit by not providing blocking access to + condition variables: code blocking while waiting for a condition will + "die". This still works with most modules/usages, and blocking calls + must not be in an interactive application, so it makes sense. ENVIRONMENT VARIABLES The following environment variables are used by this module: @@ -180,7 +432,7 @@ my $data = $fcp->client_get ($url); - 2. Blocking, but parallelizing: + 2. Blocking, but running in parallel: my @datas = map $_->result, map $fcp->txn_client_get ($_), @@ -189,9 +441,9 @@ Both blocking examples work without the module user having to know anything about events. - 3a. Event-based in a main program, using any support Event module: + 3a. Event-based in a main program, using any supported event module: - use Event; + use EV; $fcp->txn_client_get ($url)->cb (sub { my $txn = shift; @@ -199,7 +451,7 @@ ... }); - Event::loop; + EV::loop; 3b. The module user could use AnyEvent, too: @@ -215,11 +467,13 @@ $quit->wait; SEE ALSO - Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. + Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event, + Glib::Event, Glib, Coro, Tk. - Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, - AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. + Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV, + AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib, + AnyEvent::Impl::Tk, AnyEvent::Impl::Perl. - Nontrivial usage example: Net::FCP. + Nontrivial usage examples: Net::FCP, Net::XMPP2.