--- AnyEvent/lib/AnyEvent.pm 2005/04/27 01:26:44 1.1 +++ AnyEvent/lib/AnyEvent.pm 2008/04/22 05:12:19 1.54 @@ -1,52 +1,820 @@ =head1 NAME -AnyEvent - ??? +AnyEvent - provide framework for multiple event loops + +EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported event loops =head1 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 whether a condition was flagged + $w->wait; # enters "main loop" till $condvar gets ->broadcast + $w->broadcast; # wake up current and all future wait's + +=head1 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 I, AnyEvent is I and AnyEvent is I. + +First and foremost, I 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 I...), 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 +I 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 I, 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 I use this module. + + =head1 DESCRIPTION +L 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 L +module. + +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: L, L, L, +L, L, L. 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 likely make +that model the default. For example: + + use Tk; + use AnyEvent; + + # .. AnyEvent will likely default to Tk + +The I 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 +C. Like other event modules you can load it +explicitly. + +=head1 WATCHERS + +AnyEvent has the central concept of a I, 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 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 C or otherwise deleting all references +to it). + +All watchers are created by calling a method on the C class. + +Many watchers either are used with "recursion" (repeating timers for +example), or need to refer to their watcher object in other ways. + +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 C combination. This is necessary because in Perl, +my variables are only visible after the statement in which they are +declared. + +=head2 IO WATCHERS + +You can create an I/O watcher by calling the C<< AnyEvent->io >> method +with the following mandatory key-value pairs as arguments: + +C the Perl I (I file descriptor) to watch for +events. C must be a string that is either C or C, which +creates a watcher waiting for "r"eadable or "w"ritable events, +respectively. C 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: + + # 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; + }); + +=head2 TIME WATCHERS + +You can create a time watcher by calling the C<< AnyEvent->timer >> +method with the following mandatory arguments: + +C specifies after how many seconds (fractional values are +supported) should the timer activate. C 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 +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; + +Example 2: + + # fire an event after 0.5 seconds, then roughly every second + my $w; + + 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); + +=head3 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 L, which offers both relative (ev_timer) and +absolute (ev_periodic) timers. + +AnyEvent always prefers relative timers, if available, matching the +AnyEvent API. + +=head2 SIGNAL WATCHERS + +You can watch for signals using a signal watcher, C is the signal +I without any C prefix, C 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. + +The main advantage of using these watchers is that you can share a signal +between multiple watchers. + +This watcher might use C<%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 }); + +=head2 CHILD PROCESS WATCHERS + +You can also watch on a child process exit and catch its exit status. + +The child process is specified by the C argument (if set to C<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 C. The callback will be called with the pid +and exit status (as returned by waitpid). + +Example: wait for pid 1333 + + my $w = AnyEvent->child ( + pid => 1333, + cb => sub { + my ($pid, $status) = @_; + warn "pid $pid exited with status $status"; + }, + ); + +=head2 CONDITION VARIABLES + +Condition variables can be created by calling the C<< AnyEvent->condvar >> +method without any arguments. + +A condition variable waits for a condition - precisely that the C<< +->broadcast >> method has been called. + +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 C<< ->wait >> in your main +program until the user clicks the Quit button in your app, which would C<< +->broadcast >> the "quit" event. + +Note that condition variables recurse into the event loop - if you have +two pirces of code that call C<< ->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. + +This object has two methods: + +=over 4 + +=item $cv->wait + +Wait (blocking if necessary) until the C<< ->broadcast >> method has been +called on c<$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 to stay interactive), so I, 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 I to C<< ->wait >> in a module is that you cannot +sensibly have two C<< ->wait >>'s in parallel, as that would require +multiple interpreters or coroutines/threads, none of which C +can supply (the coroutine-aware backends L and +L explicitly support concurrent C<< ->wait >>'s +from different coroutines, however). + +=item $cv->broadcast + +Flag the condition as ready - a running C<< ->wait >> and all further +calls to C will (eventually) return after this method has been +called. If nobody is waiting the broadcast will be remembered.. + +=back + +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; + +=head1 GLOBAL VARIABLES AND FUNCTIONS + =over 4 +=item $AnyEvent::MODEL + +Contains C until the first watcher is being created. Then it +contains the event model that is being used, which is the name of the +Perl class implementing the model. This class is usually one of the +C modules, but can be any other class in the case +AnyEvent has been extended at runtime (e.g. in I). + +The known classes so far are: + + AnyEvent::Impl::CoroEV based on Coro::EV, best choice. + AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. + AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). + AnyEvent::Impl::Event based on Event, also second best choice :) + AnyEvent::Impl::Glib based on Glib, third-best choice. + AnyEvent::Impl::Tk based on Tk, very bad choice. + AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. + +=item AnyEvent::detect + +Returns C<$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, as late as possible at +runtime. + +=back + +=head1 WHAT TO DO IN A MODULE + +As a module author, you should C 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. + +Never call C<< ->wait >> on a condition variable unless you I that +the C<< ->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 C<< ->wait >> when the user of your module +requests it (i.e. if you create a http request object ad have a method +called C that returns the results, it should call C<< ->wait >> +freely, as the user of your module knows what she is doing. always). + +=head1 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 (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 C module, which gives you similar +behaviour everywhere, but letting AnyEvent chose is generally better. + =cut package AnyEvent; +no warnings; +use strict; + use Carp; -$VERSION = 0.1; +our $VERSION = '3.12'; +our $MODEL; -no warnings; +our $AUTOLOAD; +our @ISA; + +our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1; + +our @REGISTRY; my @models = ( - [Coro => Coro::Event::], - [Event => Event::], - [Glib => Glib::], - [Tk => Tk::], + [Coro::EV:: => AnyEvent::Impl::CoroEV::], + [Coro::Event:: => AnyEvent::Impl::CoroEvent::], + [EV:: => AnyEvent::Impl::EV::], + [Event:: => AnyEvent::Impl::Event::], + [Glib:: => AnyEvent::Impl::Glib::], + [Tk:: => AnyEvent::Impl::Tk::], + [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], ); -sub AUTOLOAD { - $AUTOLOAD =~ s/.*://; +our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY); - for (@models) { - my ($model, $package) = @$_; - if (defined ${"$package\::VERSION"}) { - $EVENT = "AnyEvent::Impl::$model"; - eval "require $EVENT"; die if $@; - goto &{"$EVENT\::$AUTOLOAD"}; +sub detect() { + unless ($MODEL) { + no strict 'refs'; + + # check for already loaded models + for (@REGISTRY, @models) { + my ($package, $model) = @$_; + if (${"$package\::VERSION"} > 0) { + if (eval "require $model") { + $MODEL = $model; + warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1; + last; + } + } } - } - for (@models) { - my ($model, $package) = @$_; - $EVENT = "AnyEvent::Impl::$model"; - if (eval "require $EVENT") { - goto &{"$EVENT\::$AUTOLOAD"}; + unless ($MODEL) { + # try to load a model + + for (@REGISTRY, @models) { + my ($package, $model) = @$_; + if (eval "require $package" + and ${"$package\::VERSION"} > 0 + and eval "require $model") { + $MODEL = $model; + warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1; + last; + } + } + + $MODEL + or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk."; } + + unshift @ISA, $MODEL; + push @{"$MODEL\::ISA"}, "AnyEvent::Base"; + } + + $MODEL +} + +sub AUTOLOAD { + (my $func = $AUTOLOAD) =~ s/.*://; + + $method{$func} + or croak "$func: not a valid method for AnyEvent objects"; + + detect unless $MODEL; + + my $class = shift; + $class->$func (@_); +} + +package AnyEvent::Base; + +# default implementation for ->condvar, ->wait, ->broadcast + +sub condvar { + bless \my $flag, "AnyEvent::Base::CondVar" +} + +sub AnyEvent::Base::CondVar::broadcast { + ${$_[0]}++; +} + +sub AnyEvent::Base::CondVar::wait { + AnyEvent->one_event while !${$_[0]}; +} + +# default implementation for ->signal + +our %SIG_CB; + +sub signal { + my (undef, %arg) = @_; + + my $signal = uc $arg{signal} + or Carp::croak "required option 'signal' is missing"; + + $SIG_CB{$signal}{$arg{cb}} = $arg{cb}; + $SIG{$signal} ||= sub { + $_->() for values %{ $SIG_CB{$signal} || {} }; + }; + + bless [$signal, $arg{cb}], "AnyEvent::Base::Signal" +} + +sub AnyEvent::Base::Signal::DESTROY { + my ($signal, $cb) = @{$_[0]}; + + delete $SIG_CB{$signal}{$cb}; + + $SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} }; +} + +# default implementation for ->child + +our %PID_CB; +our $CHLD_W; +our $CHLD_DELAY_W; +our $PID_IDLE; +our $WNOHANG; + +sub _child_wait { + while (0 < (my $pid = waitpid -1, $WNOHANG)) { + $_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }), + (values %{ $PID_CB{0} || {} }); } - die "No event module selected for AnyEvent and autodetect failed. Install any of these: Coro, Event, Glib or Tk."; + undef $PID_IDLE; +} + +sub _sigchld { + # make sure we deliver these changes "synchronous" with the event loop. + $CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub { + undef $CHLD_DELAY_W; + &_child_wait; + }); +} + +sub child { + my (undef, %arg) = @_; + + defined (my $pid = $arg{pid} + 0) + or Carp::croak "required option 'pid' is missing"; + + $PID_CB{$pid}{$arg{cb}} = $arg{cb}; + + unless ($WNOHANG) { + $WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1; + } + + unless ($CHLD_W) { + $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld); + # child could be a zombie already, so make at least one round + &_sigchld; + } + + bless [$pid, $arg{cb}], "AnyEvent::Base::Child" +} + +sub AnyEvent::Base::Child::DESTROY { + my ($pid, $cb) = @{$_[0]}; + + delete $PID_CB{$pid}{$cb}; + delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} }; + + undef $CHLD_W unless keys %PID_CB; } -1; +=head1 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 +C<@AnyEvent::REGISTRY>. You can do that before and even without loading +AnyEvent, so it is reasonably cheap. + +Example: + + push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; + +This tells AnyEvent to (literally) use the C +package/class when it finds the C 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 C the +C module. + +The class should provide implementations for all watcher types. See +L (source code), L (Source code) +and so on for actual examples. Use C to +see the sources. + +If you don't provide C and C watchers than AnyEvent will +provide suitable (hopefully) replacements. + +The above example isn't fictitious, the I (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 I, and it is updated and maintained as part of the +I distribution. + +I also cheats a bit by not providing blocking access to +condition variables: code blocking while waiting for a condition will +C. This still works with most modules/usages, and blocking calls must +not be done in an interactive application, so it makes sense. + +=head1 ENVIRONMENT VARIABLES + +The following environment variables are used by this module: + +C when set to C<2> or higher, cause AnyEvent to +report to STDERR which event model it chooses. + +=head1 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 $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 + +=head1 REAL-WORLD EXAMPLE + +Consider the L 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 C method works like C: 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 +L, and it works as simple as in any other, similar, module. + +More complicated is C: 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 C callback gets +called as soon as the event loop detects that the socket is ready for +writing. + +The C 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, C 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 C 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 (Cs, exceptions) +that occured during request processing. The C method 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. + +All of this enables the following usage styles: + +1. Blocking: + + my $data = $fcp->client_get ($url); + +2. Blocking, but running in parallel: + + 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 supported event module: + + use EV; + + $fcp->txn_client_get ($url)->cb (sub { + my $txn = shift; + my $data = $txn->result; + ... + }); + + EV::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; + +=head1 SEE ALSO + +Event modules: L, L, L, L, +L, L, L, L, L, L. + +Implementations: L, L, +L, L, +L, L, L. + +Nontrivial usage examples: L, L. + +=head1 AUTHOR + + Marc Lehmann + http://home.schmorp.de/ + +=cut + +1