[ViewVC] Annotation of: cvs/AnyEvent/README

NAME
    AnyEvent - provide framework for multiple event loops

    Event, Coro, Glib, Tk - various supported event loops

SYNOPSIS
       use AnyEvent;

       my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {
          my ($poll_got) = @_;
          ...
       });

    * only one io watcher per $fh and $poll type is allowed (i.e. on a
    socket you can have one r + one w or one rw watcher, not any more
    (limitation by Tk).

    * the $poll_got passed to the handler needs to be checked by looking for
    single characters (e.g. with a regex), as it can contain more event
    types than were requested (e.g. a 'w' watcher might generate 'rw'
    events, limitation by Glib).

    * AnyEvent will keep filehandles alive, so as long as the watcher
    exists, the filehandle exists.

       my $w = AnyEvent->timer (after => $seconds, cb => sub {
          ...
       });

    * io and time watchers get canceled whenever $w is destroyed, so keep a
    copy

    * timers can only be used once and must be recreated for repeated
    operation (limitation by Glib and Tk).

       my $w = AnyEvent->condvar; # kind of main loop replacement
       $w->wait; # enters main loop till $condvar gets ->broadcast
       $w->broadcast; # wake up current and all future wait's

    * condvars are used to give blocking behaviour when neccessary. Create a
    condvar for any "request" or "event" your module might create,
    "->broadcast" it when the event happens and provide a function that
    calls "->wait" for it. See the examples below.

DESCRIPTION
    AnyEvent provides an identical interface to multiple event loops. This
    allows module authors to utilizy 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, it will issue an error.

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 watch 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::" module
    when it finds the "urxvt" module is loaded. When AnyEvent is loaded and
    requested to find a suitable event model, it will first check for the
    urxvt module.

    The above isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) uses the
    above line exactly. 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.

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 <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

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.


Revision:	1.5
Committed:	Sun Jan 8 04:41:08 2006 UTC (18 years, 4 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_0, rel-1_02, rel-1_01
Changes since 1.4:	+23 -0 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.2	NAME
2			AnyEvent - provide framework for multiple event loops
3
4			Event, Coro, Glib, Tk - various supported event loops
5
6			SYNOPSIS
7	root	1.4	use AnyEvent;
8	root	1.2
9	root	1.3	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {
10	root	1.2	my ($poll_got) = @_;
11			...
12			});
13	root	1.3
14	root	1.4	* only one io watcher per $fh and $poll type is allowed (i.e. on a
15			socket you can have one r + one w or one rw watcher, not any more
16			(limitation by Tk).
17
18			* the $poll_got passed to the handler needs to be checked by looking for
19			single characters (e.g. with a regex), as it can contain more event
20			types than were requested (e.g. a 'w' watcher might generate 'rw'
21			events, limitation by Glib).
22	root	1.3
23	root	1.4	* AnyEvent will keep filehandles alive, so as long as the watcher
24	root	1.3	exists, the filehandle exists.
25
26			my $w = AnyEvent->timer (after => $seconds, cb => sub {
27	root	1.2	...
28			});
29
30	root	1.4	* io and time watchers get canceled whenever $w is destroyed, so keep a
31	root	1.3	copy
32
33	root	1.4	* timers can only be used once and must be recreated for repeated
34			operation (limitation by Glib and Tk).
35	root	1.2
36			my $w = AnyEvent->condvar; # kind of main loop replacement
37	root	1.3	$w->wait; # enters main loop till $condvar gets ->broadcast
38			$w->broadcast; # wake up current and all future wait's
39
40	root	1.4	* condvars are used to give blocking behaviour when neccessary. Create a
41	root	1.3	condvar for any "request" or "event" your module might create,
42			"->broadcast" it when the event happens and provide a function that
43			calls "->wait" for it. See the examples below.
44	root	1.2
45			DESCRIPTION
46			AnyEvent provides an identical interface to multiple event loops. This
47			allows module authors to utilizy an event loop without forcing module
48			users to use the same event loop (as only a single event loop can
49			coexist peacefully at any one time).
50
51			The interface itself is vaguely similar but not identical to the Event
52			module.
53
54			On the first call of any method, the module tries to detect the
55			currently loaded event loop by probing wether any of the following
56			modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is
57			used. If none is found, the module tries to load these modules in the
58			order given. The first one that could be successfully loaded will be
59			used. If still none could be found, it will issue an error.
60
61	root	1.5	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
62			If you need to support another event library which isn't directly
63			supported by AnyEvent, you can supply your own interface to it by
64			pushing, before the first watch gets created, the package name of the
65			event module and the package name of the interface to use onto
66			@AnyEvent::REGISTRY. You can do that before and even without loading
67			AnyEvent.
68
69			Example:
70
71			push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
72
73			This tells AnyEvent to (literally) use the "urxvt::anyevent::" module
74			when it finds the "urxvt" module is loaded. When AnyEvent is loaded and
75			requested to find a suitable event model, it will first check for the
76			urxvt module.
77
78			The above isn't fictitious, the rxvt-unicode (a.k.a. urxvt) uses the
79			above line exactly. An interface isn't included in AnyEvent because it
80			doesn't make sense outside the embedded interpreter inside
81			rxvt-unicode, and it is updated and maintained as part of the
82			rxvt-unicode distribution.
83
84	root	1.4	ENVIRONMENT VARIABLES
85			The following environment variables are used by this module:
86
87			"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event
88			model gets used.
89
90	root	1.2	EXAMPLE
91			The following program uses an io watcher to read data from stdin, a
92			timer to display a message once per second, and a condvar to exit the
93			program when the user enters quit:
94
95			use AnyEvent;
96
97			my $cv = AnyEvent->condvar;
98
99			my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
100			warn "io event <$_[0]>\n"; # will always output <r>
101			chomp (my $input = <STDIN>); # read a line
102			warn "read: $input\n"; # output what has been read
103			$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
104			});
105
106			my $time_watcher; # can only be used once
107
108			sub new_timer {
109			$timer = AnyEvent->timer (after => 1, cb => sub {
110			warn "timeout\n"; # print 'timeout' about every second
111			&new_timer; # and restart the time
112			});
113			}
114
115			new_timer; # create first timer
116
117			$cv->wait; # wait until user enters /^q/i
118
119	root	1.3	REAL-WORLD EXAMPLE
120			Consider the Net::FCP module. It features (among others) the following
121			API calls, which are to freenet what HTTP GET requests are to http:
122
123			my $data = $fcp->client_get ($url); # blocks
124
125			my $transaction = $fcp->txn_client_get ($url); # does not block
126			$transaction->cb ( sub { ... } ); # set optional result callback
127			my $data = $transaction->result; # possibly blocks
128
129			The "client_get" method works like "LWP::Simple::get": it requests the
130			given URL and waits till the data has arrived. It is defined to be:
131
132			sub client_get { $_[0]->txn_client_get ($_[1])->result }
133
134			And in fact is automatically generated. This is the blocking API of
135			Net::FCP, and it works as simple as in any other, similar, module.
136
137			More complicated is "txn_client_get": It only creates a transaction
138			(completion, result, ...) object and initiates the transaction.
139
140			my $txn = bless { }, Net::FCP::Txn::;
141
142			It also creates a condition variable that is used to signal the
143			completion of the request:
144
145			$txn->{finished} = AnyAvent->condvar;
146
147			It then creates a socket in non-blocking mode.
148
149			socket $txn->{fh}, ...;
150			fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
151			connect $txn->{fh}, ...
152			and !$!{EWOULDBLOCK}
153			and !$!{EINPROGRESS}
154			and Carp::croak "unable to connect: $!\n";
155
156	root	1.4	Then it creates a write-watcher which gets called whenever an error
157	root	1.3	occurs or the connection succeeds:
158
159			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
160
161			And returns this transaction object. The "fh_ready_w" callback gets
162			called as soon as the event loop detects that the socket is ready for
163			writing.
164
165			The "fh_ready_w" method makes the socket blocking again, writes the
166			request data and replaces the watcher by a read watcher (waiting for
167			reply data). The actual code is more complicated, but that doesn't
168			matter for this example:
169
170			fcntl $txn->{fh}, F_SETFL, 0;
171			syswrite $txn->{fh}, $txn->{request}
172			or die "connection or write error";
173			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
174
175			Again, "fh_ready_r" waits till all data has arrived, and then stores the
176			result and signals any possible waiters that the request ahs finished:
177
178			sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
179
180			if (end-of-file or data complete) {
181			$txn->{result} = $txn->{buf};
182			$txn->{finished}->broadcast;
183	root	1.4	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
184	root	1.3	}
185
186			The "result" method, finally, just waits for the finished signal (if the
187			request was already finished, it doesn't wait, of course, and returns
188			the data:
189
190			$txn->{finished}->wait;
191	root	1.4	return $txn->{result};
192	root	1.3
193			The actual code goes further and collects all errors ("die"s,
194			exceptions) that occured during request processing. The "result" method
195			detects wether an exception as thrown (it is stored inside the $txn
196			object) and just throws the exception, which means connection errors and
197			other problems get reported tot he code that tries to use the result,
198			not in a random callback.
199
200			All of this enables the following usage styles:
201
202			1. Blocking:
203
204			my $data = $fcp->client_get ($url);
205
206			2. Blocking, but parallelizing:
207
208			my @datas = map $_->result,
209			map $fcp->txn_client_get ($_),
210			@urls;
211
212			Both blocking examples work without the module user having to know
213			anything about events.
214
215			3a. Event-based in a main program, using any support Event module:
216
217			use Event;
218
219			$fcp->txn_client_get ($url)->cb (sub {
220			my $txn = shift;
221			my $data = $txn->result;
222			...
223			});
224
225			Event::loop;
226
227			3b. The module user could use AnyEvent, too:
228
229			use AnyEvent;
230
231			my $quit = AnyEvent->condvar;
232
233			$fcp->txn_client_get ($url)->cb (sub {
234			...
235			$quit->broadcast;
236			});
237
238			$quit->wait;
239
240	root	1.2	SEE ALSO
241	root	1.3	Event modules: Coro::Event, Coro, Event, Glib::Event, Glib.
242
243			Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event,
244			AnyEvent::Impl::Glib, AnyEvent::Impl::Tk.
245
246			Nontrivial usage example: Net::FCP.
247	root	1.2
248