--- AnyEvent/README 2006/01/08 04:41:08 1.5 +++ 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). @@ -53,15 +72,215 @@ 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 watch gets created, the package name of the + 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. @@ -70,17 +289,27 @@ push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; - This tells AnyEvent to (literally) use the "urxvt::anyevent::" module - when it finds the "urxvt" module is loaded. When AnyEvent is loaded and - requested to find a suitable event model, it will first check for the - urxvt module. + 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 exactly. An interface isn't included in AnyEvent because it + 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: @@ -203,7 +432,7 @@ my $data = $fcp->client_get ($url); - 2. Blocking, but parallelizing: + 2. Blocking, but running in parallel: my @datas = map $_->result, map $fcp->txn_client_get ($_), @@ -212,9 +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; @@ -222,7 +451,7 @@ ... }); - Event::loop; + EV::loop; 3b. The module user could use AnyEvent, too: @@ -238,11 +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.