--- AnyEvent/README 2005/04/27 01:26:44 1.1 +++ AnyEvent/README 2007/11/23 10:42:00 1.13 @@ -0,0 +1,424 @@ +NAME + AnyEvent - provide framework for multiple event loops + + Event, Coro, Glib, Tk, Perl - various supported event loops + +SYNOPSIS + use AnyEvent; + + my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { + ... + }); + + my $w = AnyEvent->timer (after => $seconds, cb => sub { + ... + }); + + 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 + +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 + 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. + + 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. + + 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. + + 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. + + 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. + + $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::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::Tk based on Tk, very bad choice. + AnyEvent::Impl::Perl pure-perl implementation, inefficient. + + 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: + + "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event + model gets used. + +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: + + 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 $time_watcher; # can only be used once + + sub new_timer { + $timer = AnyEvent->timer (after => 1, cb => sub { + warn "timeout\n"; # print 'timeout' about every second + &new_timer; # and restart the time + }); + } + + new_timer; # create first timer + + $cv->wait; # wait until user enters /^q/i + +REAL-WORLD EXAMPLE + Consider the Net::FCP module. It features (among others) the following + API calls, which are to freenet what HTTP GET requests are to http: + + my $data = $fcp->client_get ($url); # blocks + + my $transaction = $fcp->txn_client_get ($url); # does not block + $transaction->cb ( sub { ... } ); # set optional result callback + my $data = $transaction->result; # possibly blocks + + The "client_get" method works like "LWP::Simple::get": it requests the + given URL and waits till the data has arrived. It is defined to be: + + sub client_get { $_[0]->txn_client_get ($_[1])->result } + + And in fact is automatically generated. This is the blocking API of + Net::FCP, and it works as simple as in any other, similar, module. + + More complicated is "txn_client_get": It only creates a transaction + (completion, result, ...) object and initiates the transaction. + + my $txn = bless { }, Net::FCP::Txn::; + + It also creates a condition variable that is used to signal the + completion of the request: + + $txn->{finished} = AnyAvent->condvar; + + It then creates a socket in non-blocking mode. + + socket $txn->{fh}, ...; + fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; + connect $txn->{fh}, ... + and !$!{EWOULDBLOCK} + and !$!{EINPROGRESS} + and Carp::croak "unable to connect: $!\n"; + + Then it creates a write-watcher which gets called whenever an error + occurs or the connection succeeds: + + $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); + + And returns this transaction object. The "fh_ready_w" callback gets + called as soon as the event loop detects that the socket is ready for + writing. + + The "fh_ready_w" method makes the socket blocking again, writes the + request data and replaces the watcher by a read watcher (waiting for + reply data). The actual code is more complicated, but that doesn't + matter for this example: + + fcntl $txn->{fh}, F_SETFL, 0; + syswrite $txn->{fh}, $txn->{request} + or die "connection or write error"; + $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); + + Again, "fh_ready_r" waits till all data has arrived, and then stores the + result and signals any possible waiters that the request ahs finished: + + sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; + + if (end-of-file or data complete) { + $txn->{result} = $txn->{buf}; + $txn->{finished}->broadcast; + $txb->{cb}->($txn) of $txn->{cb}; # also call callback + } + + The "result" method, finally, just waits for the finished signal (if the + request was already finished, it doesn't wait, of course, and returns + the data: + + $txn->{finished}->wait; + return $txn->{result}; + + 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 + 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. + + All of this enables the following usage styles: + + 1. Blocking: + + my $data = $fcp->client_get ($url); + + 2. Blocking, but parallelizing: + + my @datas = map $_->result, + map $fcp->txn_client_get ($_), + @urls; + + 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: + + use Event; + + $fcp->txn_client_get ($url)->cb (sub { + my $txn = shift; + my $data = $txn->result; + ... + }); + + Event::loop; + + 3b. The module user could use AnyEvent, too: + + use AnyEvent; + + my $quit = AnyEvent->condvar; + + $fcp->txn_client_get ($url)->cb (sub { + ... + $quit->broadcast; + }); + + $quit->wait; + +SEE ALSO + Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. + + Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, + AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. + + Nontrivial usage example: Net::FCP. + +