--- AnyEvent/README 2006/12/11 01:16:09 1.8 +++ AnyEvent/README 2008/04/19 04:58:14 1.16 @@ -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; @@ -14,29 +15,77 @@ ... }); - my $w = AnyEvent->condvar; # stores wether a condition was flagged + my $w = AnyEvent->condvar; # stores whether a condition was flagged $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: In general, + only one event loop can be active at the same time in a process. + AnyEvent helps hiding the differences between those event loops. + + 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 a total misnomer as it 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. What's worse, all the potential users of your module + are *also* forced to use the same event loop you use. + + AnyEvent is different: 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. Again: if your + module uses one of those, every user of your module has to use it, too. + But if your module uses AnyEvent, it works transparently with all event + models it supports (including stuff like POE and IO::Async, as long as + those use one of the supported event loops. It is trivial to add new + event loops to AnyEvent, too, so it is future-proof). + + In addition to 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 up to the point, by + only offering the functionality that is necessary, 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 users to use the same event loop (as only a single event loop can coexist peacefully at any one time). - The interface itself is vaguely similar but not identical to the Event + The interface itself is vaguely similar, but not identical to the Event module. - 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. + 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: 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 stated order. 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. Because AnyEvent first checks for modules that are already loaded, - loading an Event model explicitly before first using AnyEvent will + loading an event model explicitly before first using AnyEvent will likely make that model the default. For example: use Tk; @@ -44,6 +93,10 @@ # .. AnyEvent will likely default to Tk + The *likely* means that, if any module loads another event model and + starts using it, all bets are off. Maybe you should tell their authors + to use AnyEvent so their modules work together with others seamlessly... + The pure-perl implementation of AnyEvent is called "AnyEvent::Impl::Perl". Like other event modules you can load it explicitly. @@ -55,27 +108,47 @@ 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). + callback when the event occurs (of course, only when the event model is + in control). + + To disable the watcher you have to destroy it (e.g. by setting the + variable you store it in 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: + Many watchers either are used with "recursion" (repeating timers for + example), or need to refer to their watcher object in other ways. - "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" teh 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). + An any way to achieve that is this pattern: + + my $w; $w = AnyEvent->type (arg => value ..., cb => sub { + # you can use $w here, for example to undef it + undef $w; + }); + + Note that "my $w; $w =" combination. This is necessary because in Perl, + my variables are only visible after the statement in which they are + declared. + + IO WATCHERS + You can create an I/O watcher by calling the "AnyEvent->io" method with + the following mandatory key-value pairs as arguments: - Filehandles will be kept alive, so as long as the watcher exists, the - filehandle exists, too. + "fh" the Perl *file handle* (*not* file descriptor) to watch for events. + "poll" must be a string that is either "r" or "w", which creates a + watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" + is the callback to invoke each time the file handle becomes ready. + + File handles will be kept alive, so as long as the watcher exists, the + file handle exists, too. + + It is not allowed to 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 + handles. Example: @@ -90,8 +163,9 @@ 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. + "after" specifies after how many seconds (fractional values are + supported) should the timer activate. "cb" the callback to invoke in + that case. 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 @@ -105,71 +179,150 @@ }); # to cancel the timer: - undef $w + undef $w; - CONDITION WATCHERS - Condition watchers can be created by calling the "AnyEvent->condvar" - method without any arguments. + Example 2: - A condition watcher watches for a condition - precisely that the - "->broadcast" method has been called. + # fire an event after 0.5 seconds, then roughly every second + my $w; - The watcher has only two methods: + my $cb = sub { + # cancel the old timer while creating a new one + $w = AnyEvent->timer (after => 1, cb => $cb); + }; + + # start the "loop" by creating the first watcher + $w = AnyEvent->timer (after => 0.5, cb => $cb); + + TIMING ISSUES + There are two ways to handle timers: based on real time (relative, "fire + in 10 seconds") and based on wallclock time (absolute, "fire at 12 + o'clock"). + + While most event loops expect timers to specified in a relative way, + they use absolute time internally. This makes a difference when your + clock "jumps", for example, when ntp decides to set your clock backwards + from the wrong 2014-01-01 to 2008-01-01, a watcher that you created to + fire "after" a second might actually take six years to finally fire. + + AnyEvent cannot compensate for this. The only event loop that is + conscious about these issues is EV, which offers both relative + (ev_timer) and absolute (ev_periodic) timers. - $cv->wait - Wait (blocking if necessary) until the "->broadcast" method has been - called on c<$cv>, while servicing other watchers normally. + AnyEvent always prefers relative timers, if available, matching the + AnyEvent API. - 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). + SIGNAL WATCHERS + You can watch for signals using a signal watcher, "signal" is the signal + *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked + whenever a signal occurs. + + Multiple signals 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, but it is guarenteed not to interrupt any other callbacks. - You can only wait once on a condition - additional calls will return - immediately. + The main advantage of using these watchers is that you can share a + signal between multiple watchers. - $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.. + This watcher might use %SIG, so programs overwriting those signals + directly will likely not work correctly. - Example: + Example: exit on SIGINT - # wait till the result is ready - my $result_ready = AnyEvent->condvar; + my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); - # do something such as adding a timer - # or socket watcher the calls $result_ready->broadcast - # when the "result" is ready. + CHILD PROCESS WATCHERS + You can also watch on a child process exit and catch its exit status. - $result_ready->wait; + The child process is specified by the "pid" argument (if set to 0, it + 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 "SIGCHLD". The callback will be called with the pid + and exit status (as returned by waitpid). - 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 callbakc invocation - might or might not be asynchronous. + Example: wait for pid 1333 - These watchers might use %SIG, so programs overwriting those signals - directly will likely not work correctly. + my $w = AnyEvent->child ( + pid => 1333, + cb => sub { + my ($pid, $status) = @_; + warn "pid $pid exited with status $status"; + }, + ); - Example: exit on SIGINT + CONDITION VARIABLES + Condition variables can be created by calling the "AnyEvent->condvar" + method without any arguments. - my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); + A condition variable waits for a condition - precisely that the + "->broadcast" method has been called. - CHILD PROCESS WATCHERS - You can also listen for the status of a child process specified by the - "pid" argument. The watcher will only trigger once. This works by - installing a signal handler for "SIGCHLD". + They are very useful to signal that a condition has been fulfilled, for + example, if you write a module that does asynchronous http requests, + then a condition variable would be the ideal candidate to signal the + availability of results. + + You can also use condition variables to block your main program until an + event occurs - for example, you could "->wait" in your main program + until the user clicks the Quit button in your app, which would + "->broadcast" the "quit" event. + + Note that condition variables recurse into the event loop - if you have + two pirces of code that call "->wait" in a round-robbin fashion, you + lose. Therefore, condition variables are good to export to your caller, + but you should avoid making a blocking wait yourself, at least in + callbacks, as this asks for trouble. - Example: wait for pid 1333 + This object has 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. - my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); + Not all event models support a blocking wait - some die in that case + (programs might want to do that to stay interactive), so *if you are + using this from a module, never require a blocking wait*, but let + the caller decide whether 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 + AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly + support concurrent "->wait"'s from different coroutines, however). -GLOBALS + $cv->broadcast + Flag the condition as ready - a running "->wait" and all further + calls to "wait" will (eventually) 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. + # in this case, we simply use a timer: + my $w = AnyEvent->timer ( + after => 1, + cb => sub { $result_ready->broadcast }, + ); + + # this "blocks" (while handling events) till the watcher + # calls broadcast + $result_ready->wait; + +GLOBAL VARIABLES AND FUNCTIONS $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 @@ -179,101 +332,129 @@ The known classes so far are: - AnyEvent::Impl::Coro based on Coro::Event, best choise. - AnyEvent::Impl::Event based on Event, also best choice :) - AnyEvent::Impl::Glib based on Glib, second-best choice. + 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. + 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. + would have created an AnyEvent watcher anyway, that is, as late as + possible 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 + 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. + Never call "->wait" on a condition variable unless you *know* that the + "->broadcast" method has been called on it already. This is because it + will stall the whole program, and the whole point of using events is to + stay interactive. + + It is fine, however, to call "->wait" when the user of your module + requests it (i.e. if you create a http request object ad have a method + called "results" that returns the results, it should call "->wait" + freely, as the user of your module knows what she is doing. always). + 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. + do anything special (it does not need to be event-based) and let + AnyEvent decide which implementation to chose if some module relies on + it. + + If the main program relies on a specific event model. For example, in + Gtk2 programs you have to rely on the Glib module. You should load the + event module before loading AnyEvent or any module that uses it: + generally speaking, you should load it 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. + loading the "AnyEvent::Impl::Perl" module, which gives you similar + behaviour everywhere, but letting AnyEvent chose is generally better. SUPPLYING YOUR OWN EVENT MODEL INTERFACE + This is an advanced topic that you do not normally need to use AnyEvent + in a module. This section is only of use to event loop authors who want + to provide AnyEvent compatibility. + 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. + AnyEvent, so it is reasonably cheap. 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. + package/class when it finds the "urxvt" package/module is already + loaded. + + When AnyEvent is loaded and asked to find a suitable event model, it + will first check for the presence of urxvt by trying to "use" the + "urxvt::anyevent" module. + + The class should provide implementations for all watcher types. See + AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and + so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see + the sources. + + If you don't provide "signal" and "child" watchers than AnyEvent will + provide suitable (hopefully) replacements. + + The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) + terminal emulator 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 appliation, so it makes sense. + must not be done in an interactive application, so it makes sense. ENVIRONMENT VARIABLES The following environment variables are used by this module: - "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event - model gets used. + "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, cause AnyEvent to + report to STDERR which event model it chooses. -EXAMPLE - The following program uses an io watcher to read data from stdin, a - timer to display a message once per second, and a condvar to exit the - program when the user enters quit: +EXAMPLE PROGRAM + The following program uses an IO 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: use AnyEvent; my $cv = AnyEvent->condvar; - my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { - warn "io event <$_[0]>\n"; # will always output - chomp (my $input = ); # read a line - warn "read: $input\n"; # output what has been read - $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i - }); + my $io_watcher = AnyEvent->io ( + fh => \*STDIN, + poll => 'r', + cb => sub { + warn "io event <$_[0]>\n"; # will always output + chomp (my $input = ); # read a line + warn "read: $input\n"; # output what has been read + $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i + }, + ); my $time_watcher; # can only be used once @@ -364,7 +545,7 @@ The actual code goes further and collects all errors ("die"s, exceptions) that occured during request processing. The "result" method - detects wether an exception as thrown (it is stored inside the $txn + detects whether an exception as thrown (it is stored inside the $txn object) and just throws the exception, which means connection errors and other problems get reported tot he code that tries to use the result, not in a random callback. @@ -375,7 +556,7 @@ my $data = $fcp->client_get ($url); - 2. Blocking, but parallelizing: + 2. Blocking, but running in parallel: my @datas = map $_->result, map $fcp->txn_client_get ($_), @@ -384,9 +565,9 @@ 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; @@ -394,7 +575,7 @@ ... }); - Event::loop; + EV::loop; 3b. The module user could use AnyEvent, too: @@ -410,11 +591,13 @@ $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.