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 GLOBALS

=over 4

=item $AnyEvent::MODEL

Contains C<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
C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).

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::Tk        based on Tk, very bad choice.
   AnyEvent::Impl::Perl      pure-perl implementation, inefficient.

=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 = '2.1';
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:	1.17
Committed:	Fri Nov 24 14:40:13 2006 UTC (17 years, 7 months ago) by root
Branch:	MAIN
CVS Tags:	rel-2_1
Changes since 1.16:	+1 -1 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	AnyEvent - provide framework for multiple event loops
4
5	Event, Coro, Glib, Tk, Perl - various supported event loops
6
7	=head1 SYNOPSIS
8
9	use AnyEvent;
10
11	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
12	...
13	});
14
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...
17	});
18
19	my $w = AnyEvent->condvar; # stores wether a condition was flagged
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast
21	$w->broadcast; # wake up current and all future wait's
22
23	=head1 DESCRIPTION
24
25	L<AnyEvent> provides an identical interface to multiple event loops. This
26	allows module authors to utilise an event loop without forcing module
27	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	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
126	=over 4
127
128	=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 GLOBALS
163
164	=over 4
165
166	=item $AnyEvent::MODEL
167
168	Contains C<undef> until the first watcher is being created. Then it
169	contains the event model that is being used, which is the name of the
170	Perl class implementing the model. This class is usually one of the
171	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
172	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
173
174	The known classes so far are:
175
176	AnyEvent::Impl::Coro based on Coro::Event, best choise.
177	AnyEvent::Impl::Event based on Event, also best choice :)
178	AnyEvent::Impl::Glib based on Glib, second-best choice.
179	AnyEvent::Impl::Tk based on Tk, very bad choice.
180	AnyEvent::Impl::Perl pure-perl implementation, inefficient.
181
182	=back
183
184	=head1 WHAT TO DO IN A MODULE
185
186	As a module author, you should "use AnyEvent" and call AnyEvent methods
187	freely, but you should not load a specific event module or rely on it.
188
189	Be careful when you create watchers in the module body - Anyevent will
190	decide which event module to use as soon as the first method is called, so
191	by calling AnyEvent in your module body you force the user of your module
192	to load the event module first.
193
194	=head1 WHAT TO DO IN THE MAIN PROGRAM
195
196	There will always be a single main program - the only place that should
197	dictate which event model to use.
198
199	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
200	do anything special and let AnyEvent decide which implementation to chose.
201
202	If the main program relies on a specific event model (for example, in Gtk2
203	programs you have to rely on either Glib or Glib::Event), you should load
204	it before loading AnyEvent or any module that uses it, generally, as early
205	as possible. The reason is that modules might create watchers when they
206	are loaded, and AnyEvent will decide on the event model to use as soon as
207	it creates watchers, and it might chose the wrong one unless you load the
208	correct one yourself.
209
210	You can chose to use a rather inefficient pure-perl implementation by
211	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is
212	generally better.
213
214	=cut
215
216	package AnyEvent;
217
218	no warnings;
219	use strict 'vars';
220	use Carp;
221
222	our $VERSION = '2.1';
223	our $MODEL;
224
225	our $AUTOLOAD;
226	our @ISA;
227
228	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
229
230	our @REGISTRY;
231
232	my @models = (
233	[Coro::Event:: => AnyEvent::Impl::Coro::],
234	[Event:: => AnyEvent::Impl::Event::],
235	[Glib:: => AnyEvent::Impl::Glib::],
236	[Tk:: => AnyEvent::Impl::Tk::],
237	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
238	);
239
240	our %method = map +($_ => 1), qw(io timer condvar broadcast wait DESTROY);
241
242	sub AUTOLOAD {
243	$AUTOLOAD =~ s/.*://;
244
245	$method{$AUTOLOAD}
246	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";
247
248	unless ($MODEL) {
249	# check for already loaded models
250	for (@REGISTRY, @models) {
251	my ($package, $model) = @$_;
252	if (${"$package\::VERSION"} > 0) {
253	if (eval "require $model") {
254	$MODEL = $model;
255	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;
256	last;
257	}
258	}
259	}
260
261	unless ($MODEL) {
262	# try to load a model
263
264	for (@REGISTRY, @models) {
265	my ($package, $model) = @$_;
266	if (eval "require $model") {
267	$MODEL = $model;
268	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
269	last;
270	}
271	}
272
273	$MODEL
274	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";
275	}
276	}
277
278	@ISA = $MODEL;
279
280	my $class = shift;
281	$class->$AUTOLOAD (@_);
282	}
283
284	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
285
286	If you need to support another event library which isn't directly
287	supported by AnyEvent, you can supply your own interface to it by
288	pushing, before the first watcher gets created, the package name of
289	the event module and the package name of the interface to use onto
290	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
291	AnyEvent.
292
293	Example:
294
295	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
296
297	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
298	package/class when it finds the C<urxvt> package/module is loaded. When
299	AnyEvent is loaded and asked to find a suitable event model, it will
300	first check for the presence of urxvt.
301
302	The class should prove implementations for all watcher types (see
303	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>
304	(Source code) and so on for actual examples, use C<perldoc -m
305	AnyEvent::Impl::Glib> to see the sources).
306
307	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
308	uses the above line as-is. An interface isn't included in AnyEvent
309	because it doesn't make sense outside the embedded interpreter inside
310	I<rxvt-unicode>, and it is updated and maintained as part of the
311	I<rxvt-unicode> distribution.
312
313	I<rxvt-unicode> also cheats a bit by not providing blocking access to
314	condition variables: code blocking while waiting for a condition will
315	C<die>. This still works with most modules/usages, and blocking calls must
316	not be in an interactive appliation, so it makes sense.
317
318	=head1 ENVIRONMENT VARIABLES
319
320	The following environment variables are used by this module:
321
322	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
323	model gets used.
324
325	=head1 EXAMPLE
326
327	The following program uses an io watcher to read data from stdin, a timer
328	to display a message once per second, and a condvar to exit the program
329	when the user enters quit:
330
331	use AnyEvent;
332
333	my $cv = AnyEvent->condvar;
334
335	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
336	warn "io event <$_[0]>\n"; # will always output <r>
337	chomp (my $input = <STDIN>); # read a line
338	warn "read: $input\n"; # output what has been read
339	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
340	});
341
342	my $time_watcher; # can only be used once
343
344	sub new_timer {
345	$timer = AnyEvent->timer (after => 1, cb => sub {
346	warn "timeout\n"; # print 'timeout' about every second
347	&new_timer; # and restart the time
348	});
349	}
350
351	new_timer; # create first timer
352
353	$cv->wait; # wait until user enters /^q/i
354
355	=head1 REAL-WORLD EXAMPLE
356
357	Consider the L<Net::FCP> module. It features (among others) the following
358	API calls, which are to freenet what HTTP GET requests are to http:
359
360	my $data = $fcp->client_get ($url); # blocks
361
362	my $transaction = $fcp->txn_client_get ($url); # does not block
363	$transaction->cb ( sub { ... } ); # set optional result callback
364	my $data = $transaction->result; # possibly blocks
365
366	The C<client_get> method works like C<LWP::Simple::get>: it requests the
367	given URL and waits till the data has arrived. It is defined to be:
368
369	sub client_get { $_[0]->txn_client_get ($_[1])->result }
370
371	And in fact is automatically generated. This is the blocking API of
372	L<Net::FCP>, and it works as simple as in any other, similar, module.
373
374	More complicated is C<txn_client_get>: It only creates a transaction
375	(completion, result, ...) object and initiates the transaction.
376
377	my $txn = bless { }, Net::FCP::Txn::;
378
379	It also creates a condition variable that is used to signal the completion
380	of the request:
381
382	$txn->{finished} = AnyAvent->condvar;
383
384	It then creates a socket in non-blocking mode.
385
386	socket $txn->{fh}, ...;
387	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
388	connect $txn->{fh}, ...
389	and !$!{EWOULDBLOCK}
390	and !$!{EINPROGRESS}
391	and Carp::croak "unable to connect: $!\n";
392
393	Then it creates a write-watcher which gets called whenever an error occurs
394	or the connection succeeds:
395
396	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
397
398	And returns this transaction object. The C<fh_ready_w> callback gets
399	called as soon as the event loop detects that the socket is ready for
400	writing.
401
402	The C<fh_ready_w> method makes the socket blocking again, writes the
403	request data and replaces the watcher by a read watcher (waiting for reply
404	data). The actual code is more complicated, but that doesn't matter for
405	this example:
406
407	fcntl $txn->{fh}, F_SETFL, 0;
408	syswrite $txn->{fh}, $txn->{request}
409	or die "connection or write error";
410	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
411
412	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
413	result and signals any possible waiters that the request ahs finished:
414
415	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
416
417	if (end-of-file or data complete) {
418	$txn->{result} = $txn->{buf};
419	$txn->{finished}->broadcast;
420	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
421	}
422
423	The C<result> method, finally, just waits for the finished signal (if the
424	request was already finished, it doesn't wait, of course, and returns the
425	data:
426
427	$txn->{finished}->wait;
428	return $txn->{result};
429
430	The actual code goes further and collects all errors (C<die>s, exceptions)
431	that occured during request processing. The C<result> method detects
432	wether an exception as thrown (it is stored inside the $txn object)
433	and just throws the exception, which means connection errors and other
434	problems get reported tot he code that tries to use the result, not in a
435	random callback.
436
437	All of this enables the following usage styles:
438
439	1. Blocking:
440
441	my $data = $fcp->client_get ($url);
442
443	2. Blocking, but parallelizing:
444
445	my @datas = map $_->result,
446	map $fcp->txn_client_get ($_),
447	@urls;
448
449	Both blocking examples work without the module user having to know
450	anything about events.
451
452	3a. Event-based in a main program, using any support Event module:
453
454	use Event;
455
456	$fcp->txn_client_get ($url)->cb (sub {
457	my $txn = shift;
458	my $data = $txn->result;
459	...
460	});
461
462	Event::loop;
463
464	3b. The module user could use AnyEvent, too:
465
466	use AnyEvent;
467
468	my $quit = AnyEvent->condvar;
469
470	$fcp->txn_client_get ($url)->cb (sub {
471	...
472	$quit->broadcast;
473	});
474
475	$quit->wait;
476
477	=head1 SEE ALSO
478
479	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.
480
481	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.
482
483	Nontrivial usage example: L<Net::FCP>.
484
485	=head1
486
487	=cut
488
489	1
490