--- AnyEvent/README 2007/11/23 10:42:00 1.13 +++ AnyEvent/README 2008/04/16 15:10:10 1.15 @@ -1,7 +1,8 @@ NAME AnyEvent - provide framework for multiple event loops - Event, Coro, Glib, Tk, Perl - various supported event loops + EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported + event loops SYNOPSIS use AnyEvent; @@ -18,6 +19,48 @@ $w->wait; # enters "main loop" till $condvar gets ->broadcast $w->broadcast; # wake up current and all future wait's +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 utilise an event loop without forcing module @@ -29,11 +72,11 @@ 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, AnyEvent will fall back to a - pure-perl event loop, which is also not very efficient. + 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 @@ -70,10 +113,6 @@ watcher waiting for "r"eadable or "w"ritable events. "cb" the callback to invoke everytime the filehandle becomes ready. - Only one io watcher per "fh" and "poll" combination is allowed (i.e. on - a socket you can have one r + one w, not any more (limitation comes from - Tk - if you are sure you are not using Tk this limitation is gone). - Filehandles will be kept alive, so as long as the watcher exists, the filehandle exists, too. @@ -114,23 +153,37 @@ 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. - Not all event models support a blocking wait - some die in that - case, 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 blockign - waits if the caller so desires). - 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 @@ -182,12 +235,12 @@ 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::Coro based on Coro::Event, second best choice. AnyEvent::Impl::Event based on Event, also second best choice :) - AnyEvent::Impl::Glib based on Glib, 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. + AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. AnyEvent::detect Returns $AnyEvent::MODEL, forcing autodetection of the event model @@ -379,7 +432,7 @@ my $data = $fcp->client_get ($url); - 2. Blocking, but parallelizing: + 2. Blocking, but running in parallel: my @datas = map $_->result, map $fcp->txn_client_get ($_), @@ -388,9 +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; @@ -398,7 +451,7 @@ ... }); - Event::loop; + EV::loop; 3b. The module user could use AnyEvent, too: @@ -414,11 +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.