AnyEvent/lib/AnyEvent.pm

=head1 NAME

AnyEvent - provide framework for multiple event loops

Event, Coro, 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 wether a condition was flagged
   $w->wait; # enters "main loop" till $condvar gets ->broadcast
   $w->broadcast; # wake up current and all future wait's

=head1 DESCRIPTION

L<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: L<Coro::Event>, L<Event>, L<Glib>, L<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
C<AnyEvent::Impl::Perl>. Like other event modules you can load it
explicitly.

=head1 WATCHERS

AnyEvent has the central concept of a I<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 C<undef> or otherwise deleting all
references to it).

All watchers are created by calling a method on the C<AnyEvent> class.

=head2 IO WATCHERS

You can create I/O watcher by calling the C<< AnyEvent->io >> method with
the following mandatory arguments:

C<fh> the Perl I<filehandle> (not filedescriptor) to watch for
events. C<poll> must be a string that is either C<r> or C<w>, that creates
a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback
to invoke everytime the filehandle becomes ready.

Only one io watcher per C<fh> and C<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 = <STDIN>);
      warn "read: $input\n";
      undef $w;
   });

=head2 TIMER WATCHERS

You can create a timer watcher by calling the C<< AnyEvent->timer >>
method with the following mandatory arguments:

C<after> after how many seconds (fractions are supported) should the timer
activate. C<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

=head2 CONDITION WATCHERS

Condition watchers can be created by calling the C<< AnyEvent->condvar >>
method without any arguments.

A condition watcher watches for a condition - precisely that the C<<
->broadcast >> method has been called.

The watcher has only 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.

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.

=item $cv->broadcast

Flag the condition as ready - a running C<< ->wait >> and all further
calls to C<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;

=back

=head1 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.

=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 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 C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is
generally better.

=cut

package AnyEvent;

no warnings;
use strict 'vars';
use Carp;

our $VERSION = '1.02';
our $MODEL;

our $AUTOLOAD;
our @ISA;

our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;

our @REGISTRY;

my @models = (
      [Coro::Event::          => AnyEvent::Impl::Coro::],
      [Event::                => AnyEvent::Impl::Event::],
      [Glib::                 => AnyEvent::Impl::Glib::],
      [Tk::                   => AnyEvent::Impl::Tk::],
      [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
);

our %method = map +($_ => 1), qw(io timer condvar broadcast wait DESTROY);

sub AUTOLOAD {
   $AUTOLOAD =~ s/.*://;

   $method{$AUTOLOAD}
      or croak "$AUTOLOAD: not a valid method for AnyEvent objects";

   unless ($MODEL) {
      # check for already loaded models
      for (@REGISTRY, @models) {
         my ($package, $model) = @$_;
         if (${"$package\::VERSION"} > 0) {
            if (eval "require $model") {
               $MODEL = $model;
               warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;
               last;
            }
         }
      }

      unless ($MODEL) {
         # try to load a model

         for (@REGISTRY, @models) {
            my ($package, $model) = @$_;
            if (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: Coro, Event, Glib or Tk.";
      }
   }

   @ISA = $MODEL;

   my $class = shift;
   $class->$AUTOLOAD (@_);
}

=head1 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
C<@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 C<urxvt::anyevent::>
package/class when it finds the C<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 prove implementations for all watcher types (see
L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>
(Source code) and so on for actual examples, use C<perldoc -m
AnyEvent::Impl::Glib> to see the sources).

The above isn't fictitious, the I<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
I<rxvt-unicode>, and it is updated and maintained as part of the
I<rxvt-unicode> distribution.

I<rxvt-unicode> also cheats a bit by not providing blocking access to
condition variables: code blocking while waiting for a condition will
C<die>. This still works with most modules/usages, and blocking calls must
not be in an interactive appliation, so it makes sense.

=head1 ENVIRONMENT VARIABLES

The following environment variables are used by this module:

C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
model gets used.

=head1 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 <r>
      chomp (my $input = <STDIN>); # 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<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 C<client_get> method works like C<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
L<Net::FCP>, and it works as simple as in any other, similar, module.

More complicated is C<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 C<fh_ready_w> callback gets
called as soon as the event loop detects that the socket is ready for
writing.

The C<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, C<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 C<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 (C<die>s, exceptions)
that occured during request processing. The C<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;

=head1 SEE ALSO

Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.

Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.

Nontrivial usage example: L<Net::FCP>.

=head1

=cut

1

Revision:	1.14
Committed:	Mon Oct 30 20:52:24 2006 UTC (17 years, 8 months ago) by root
Branch:	MAIN
Changes since 1.13:	+161 -35 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3	root	1.2	AnyEvent - provide framework for multiple event loops
4
5	root	1.14	Event, Coro, Glib, Tk, Perl - various supported event loops
6	root	1.1
7			=head1 SYNOPSIS
8
9	root	1.7	use AnyEvent;
10	root	1.2
11	root	1.14	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
12	root	1.2	...
13			});
14	root	1.5
15			my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	root	1.2	...
17			});
18
19	root	1.14	my $w = AnyEvent->condvar; # stores wether a condition was flagged
20			$w->wait; # enters "main loop" till $condvar gets ->broadcast
21	root	1.5	$w->broadcast; # wake up current and all future wait's
22
23	root	1.1	=head1 DESCRIPTION
24
25	root	1.2	L<AnyEvent> provides an identical interface to multiple event loops. This
26	root	1.13	allows module authors to utilise an event loop without forcing module
27	root	1.2	users to use the same event loop (as only a single event loop can coexist
28			peacefully at any one time).
29
30			The interface itself is vaguely similar but not identical to the Event
31			module.
32
33			On the first call of any method, the module tries to detect the currently
34			loaded event loop by probing wether any of the following modules is
35			loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is
36			used. If none is found, the module tries to load these modules in the
37			order given. The first one that could be successfully loaded will be
38	root	1.14	used. If still none could be found, AnyEvent will fall back to a pure-perl
39			event loop, which is also not very efficient.
40
41			Because AnyEvent first checks for modules that are already loaded, loading
42			an Event model explicitly before first using AnyEvent will likely make
43			that model the default. For example:
44
45			use Tk;
46			use AnyEvent;
47
48			# .. AnyEvent will likely default to Tk
49
50			The pure-perl implementation of AnyEvent is called
51			C<AnyEvent::Impl::Perl>. Like other event modules you can load it
52			explicitly.
53
54			=head1 WATCHERS
55
56			AnyEvent has the central concept of a I<watcher>, which is an object that
57			stores relevant data for each kind of event you are waiting for, such as
58			the callback to call, the filehandle to watch, etc.
59
60			These watchers are normal Perl objects with normal Perl lifetime. After
61			creating a watcher it will immediately "watch" for events and invoke
62			the callback. To disable the watcher you have to destroy it (e.g. by
63			setting the variable that stores it to C<undef> or otherwise deleting all
64			references to it).
65
66			All watchers are created by calling a method on the C<AnyEvent> class.
67
68			=head2 IO WATCHERS
69
70			You can create I/O watcher by calling the C<< AnyEvent->io >> method with
71			the following mandatory arguments:
72
73			C<fh> the Perl I<filehandle> (not filedescriptor) to watch for
74			events. C<poll> must be a string that is either C<r> or C<w>, that creates
75			a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback
76			to invoke everytime the filehandle becomes ready.
77
78			Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on
79			a socket you can have one r + one w, not any more (limitation comes from
80			Tk - if you are sure you are not using Tk this limitation is gone).
81
82			Filehandles will be kept alive, so as long as the watcher exists, the
83			filehandle exists, too.
84
85			Example:
86
87			# wait for readability of STDIN, then read a line and disable the watcher
88			my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
89			chomp (my $input = <STDIN>);
90			warn "read: $input\n";
91			undef $w;
92			});
93
94			=head2 TIMER WATCHERS
95
96			You can create a timer watcher by calling the C<< AnyEvent->timer >>
97			method with the following mandatory arguments:
98
99			C<after> after how many seconds (fractions are supported) should the timer
100			activate. C<cb> the callback to invoke.
101
102			The timer callback will be invoked at most once: if you want a repeating
103			timer you have to create a new watcher (this is a limitation by both Tk
104			and Glib).
105
106			Example:
107
108			# fire an event after 7.7 seconds
109			my $w = AnyEvent->timer (after => 7.7, cb => sub {
110			warn "timeout\n";
111			});
112
113			# to cancel the timer:
114			undef $w
115
116			=head2 CONDITION WATCHERS
117
118			Condition watchers can be created by calling the C<< AnyEvent->condvar >>
119			method without any arguments.
120
121			A condition watcher watches for a condition - precisely that the C<<
122			->broadcast >> method has been called.
123
124			The watcher has only two methods:
125	root	1.2
126	root	1.1	=over 4
127
128	root	1.14	=item $cv->wait
129
130			Wait (blocking if necessary) until the C<< ->broadcast >> method has been
131			called on c<$cv>, while servicing other watchers normally.
132
133			Not all event models support a blocking wait - some die in that case, so
134			if you are using this from a module, never require a blocking wait, but
135			let the caller decide wether the call will block or not (for example,
136			by coupling condition variables with some kind of request results and
137			supporting callbacks so the caller knows that getting the result will not
138			block, while still suppporting blockign waits if the caller so desires).
139
140			You can only wait once on a condition - additional calls will return
141			immediately.
142
143			=item $cv->broadcast
144
145			Flag the condition as ready - a running C<< ->wait >> and all further
146			calls to C<wait> will return after this method has been called. If nobody
147			is waiting the broadcast will be remembered..
148
149			Example:
150
151			# wait till the result is ready
152			my $result_ready = AnyEvent->condvar;
153
154			# do something such as adding a timer
155			# or socket watcher the calls $result_ready->broadcast
156			# when the "result" is ready.
157
158			$result_ready->wait;
159
160			=back
161
162			=head1 WHAT TO DO IN A MODULE
163
164			As a module author, you should "use AnyEvent" and call AnyEvent methods
165			freely, but you should not load a specific event module or rely on it.
166
167			Be careful when you create watchers in the module body - Anyevent will
168			decide which event module to use as soon as the first method is called, so
169			by calling AnyEvent in your module body you force the user of your module
170			to load the event module first.
171
172			=head1 WHAT TO DO IN THE MAIN PROGRAM
173
174			There will always be a single main program - the only place that should
175			dictate which event model to use.
176
177			If it doesn't care, it can just "use AnyEvent" and use it itself, or not
178			do anything special and let AnyEvent decide which implementation to chose.
179
180			If the main program relies on a specific event model (for example, in Gtk2
181			programs you have to rely on either Glib or Glib::Event), you should load
182			it before loading AnyEvent or any module that uses it, generally, as early
183			as possible. The reason is that modules might create watchers when they
184			are loaded, and AnyEvent will decide on the event model to use as soon as
185			it creates watchers, and it might chose the wrong one unless you load the
186			correct one yourself.
187
188			You can chose to use a rather inefficient pure-perl implementation by
189			loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is
190			generally better.
191
192	root	1.1	=cut
193
194			package AnyEvent;
195
196	root	1.2	no warnings;
197			use strict 'vars';
198	root	1.1	use Carp;
199
200	root	1.10	our $VERSION = '1.02';
201	root	1.2	our $MODEL;
202	root	1.1
203	root	1.2	our $AUTOLOAD;
204			our @ISA;
205	root	1.1
206	root	1.7	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
207
208	root	1.8	our @REGISTRY;
209
210	root	1.1	my @models = (
211	root	1.14	[Coro::Event:: => AnyEvent::Impl::Coro::],
212			[Event:: => AnyEvent::Impl::Event::],
213			[Glib:: => AnyEvent::Impl::Glib::],
214			[Tk:: => AnyEvent::Impl::Tk::],
215			[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
216	root	1.1	);
217
218	root	1.14	our %method = map +($_ => 1), qw(io timer condvar broadcast wait DESTROY);
219	root	1.3
220	root	1.1	sub AUTOLOAD {
221			$AUTOLOAD =~ s/.*://;
222
223	root	1.3	$method{$AUTOLOAD}
224			or croak "$AUTOLOAD: not a valid method for AnyEvent objects";
225
226	root	1.2	unless ($MODEL) {
227			# check for already loaded models
228	root	1.8	for (@REGISTRY, @models) {
229			my ($package, $model) = @$_;
230	root	1.7	if (${"$package\::VERSION"} > 0) {
231	root	1.8	if (eval "require $model") {
232			$MODEL = $model;
233			warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;
234			last;
235			}
236	root	1.2	}
237	root	1.1	}
238
239	root	1.2	unless ($MODEL) {
240			# try to load a model
241
242	root	1.8	for (@REGISTRY, @models) {
243			my ($package, $model) = @$_;
244			if (eval "require $model") {
245			$MODEL = $model;
246			warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
247			last;
248			}
249	root	1.2	}
250
251			$MODEL
252			or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";
253	root	1.1	}
254			}
255
256	root	1.2	@ISA = $MODEL;
257
258			my $class = shift;
259			$class->$AUTOLOAD (@_);
260	root	1.1	}
261
262	root	1.8	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
263
264			If you need to support another event library which isn't directly
265			supported by AnyEvent, you can supply your own interface to it by
266	root	1.11	pushing, before the first watcher gets created, the package name of
267	root	1.8	the event module and the package name of the interface to use onto
268			C<@AnyEvent::REGISTRY>. You can do that before and even without loading
269			AnyEvent.
270
271			Example:
272
273			push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
274
275	root	1.12	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
276			package/class when it finds the C<urxvt> package/module is loaded. When
277			AnyEvent is loaded and asked to find a suitable event model, it will
278			first check for the presence of urxvt.
279
280			The class should prove implementations for all watcher types (see
281			L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>
282			(Source code) and so on for actual examples, use C<perldoc -m
283			AnyEvent::Impl::Glib> to see the sources).
284	root	1.8
285	root	1.12	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
286			uses the above line as-is. An interface isn't included in AnyEvent
287	root	1.8	because it doesn't make sense outside the embedded interpreter inside
288			I<rxvt-unicode>, and it is updated and maintained as part of the
289			I<rxvt-unicode> distribution.
290
291	root	1.12	I<rxvt-unicode> also cheats a bit by not providing blocking access to
292			condition variables: code blocking while waiting for a condition will
293			C<die>. This still works with most modules/usages, and blocking calls must
294			not be in an interactive appliation, so it makes sense.
295
296	root	1.7	=head1 ENVIRONMENT VARIABLES
297
298			The following environment variables are used by this module:
299
300			C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
301			model gets used.
302
303	root	1.2	=head1 EXAMPLE
304
305			The following program uses an io watcher to read data from stdin, a timer
306			to display a message once per second, and a condvar to exit the program
307			when the user enters quit:
308
309			use AnyEvent;
310
311			my $cv = AnyEvent->condvar;
312
313			my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
314			warn "io event <$_[0]>\n"; # will always output <r>
315			chomp (my $input = <STDIN>); # read a line
316			warn "read: $input\n"; # output what has been read
317			$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
318			});
319
320			my $time_watcher; # can only be used once
321
322			sub new_timer {
323			$timer = AnyEvent->timer (after => 1, cb => sub {
324			warn "timeout\n"; # print 'timeout' about every second
325			&new_timer; # and restart the time
326			});
327			}
328
329			new_timer; # create first timer
330
331			$cv->wait; # wait until user enters /^q/i
332
333	root	1.5	=head1 REAL-WORLD EXAMPLE
334
335			Consider the L<Net::FCP> module. It features (among others) the following
336			API calls, which are to freenet what HTTP GET requests are to http:
337
338			my $data = $fcp->client_get ($url); # blocks
339
340			my $transaction = $fcp->txn_client_get ($url); # does not block
341			$transaction->cb ( sub { ... } ); # set optional result callback
342			my $data = $transaction->result; # possibly blocks
343
344			The C<client_get> method works like C<LWP::Simple::get>: it requests the
345			given URL and waits till the data has arrived. It is defined to be:
346
347			sub client_get { $_[0]->txn_client_get ($_[1])->result }
348
349			And in fact is automatically generated. This is the blocking API of
350			L<Net::FCP>, and it works as simple as in any other, similar, module.
351
352			More complicated is C<txn_client_get>: It only creates a transaction
353			(completion, result, ...) object and initiates the transaction.
354
355			my $txn = bless { }, Net::FCP::Txn::;
356
357			It also creates a condition variable that is used to signal the completion
358			of the request:
359
360			$txn->{finished} = AnyAvent->condvar;
361
362			It then creates a socket in non-blocking mode.
363
364			socket $txn->{fh}, ...;
365			fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
366			connect $txn->{fh}, ...
367			and !$!{EWOULDBLOCK}
368			and !$!{EINPROGRESS}
369			and Carp::croak "unable to connect: $!\n";
370
371	root	1.6	Then it creates a write-watcher which gets called whenever an error occurs
372	root	1.5	or the connection succeeds:
373
374			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
375
376			And returns this transaction object. The C<fh_ready_w> callback gets
377			called as soon as the event loop detects that the socket is ready for
378			writing.
379
380			The C<fh_ready_w> method makes the socket blocking again, writes the
381			request data and replaces the watcher by a read watcher (waiting for reply
382			data). The actual code is more complicated, but that doesn't matter for
383			this example:
384
385			fcntl $txn->{fh}, F_SETFL, 0;
386			syswrite $txn->{fh}, $txn->{request}
387			or die "connection or write error";
388			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
389
390			Again, C<fh_ready_r> waits till all data has arrived, and then stores the
391			result and signals any possible waiters that the request ahs finished:
392
393			sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
394
395			if (end-of-file or data complete) {
396			$txn->{result} = $txn->{buf};
397			$txn->{finished}->broadcast;
398	root	1.6	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
399	root	1.5	}
400
401			The C<result> method, finally, just waits for the finished signal (if the
402			request was already finished, it doesn't wait, of course, and returns the
403			data:
404
405			$txn->{finished}->wait;
406	root	1.6	return $txn->{result};
407	root	1.5
408			The actual code goes further and collects all errors (C<die>s, exceptions)
409			that occured during request processing. The C<result> method detects
410			wether an exception as thrown (it is stored inside the $txn object)
411			and just throws the exception, which means connection errors and other
412			problems get reported tot he code that tries to use the result, not in a
413			random callback.
414
415			All of this enables the following usage styles:
416
417			1. Blocking:
418
419			my $data = $fcp->client_get ($url);
420
421			2. Blocking, but parallelizing:
422
423			my @datas = map $_->result,
424			map $fcp->txn_client_get ($_),
425			@urls;
426
427			Both blocking examples work without the module user having to know
428			anything about events.
429
430			3a. Event-based in a main program, using any support Event module:
431
432			use Event;
433
434			$fcp->txn_client_get ($url)->cb (sub {
435			my $txn = shift;
436			my $data = $txn->result;
437			...
438			});
439
440			Event::loop;
441
442			3b. The module user could use AnyEvent, too:
443
444			use AnyEvent;
445
446			my $quit = AnyEvent->condvar;
447
448			$fcp->txn_client_get ($url)->cb (sub {
449			...
450			$quit->broadcast;
451			});
452
453			$quit->wait;
454
455	root	1.2	=head1 SEE ALSO
456
457	root	1.5	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.
458
459			Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.
460
461			Nontrivial usage example: L<Net::FCP>.
462	root	1.2
463			=head1
464
465			=cut
466
467			1
468	root	1.1