[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.

    - 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

       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.

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 wehnever 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;
       }

    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->{buf};

    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:	1.3
Committed:	Sun Dec 4 09:44:32 2005 UTC (20 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_3
Changes since 1.2:	+147 -12 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			use AnyEvent;
8
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			- 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
17			- AnyEvent will keep filehandles alive, so as long as the watcher
18			exists, the filehandle exists.
19
20			my $w = AnyEvent->timer (after => $seconds, cb => sub {
21	root	1.2	...
22			});
23
24	root	1.3	- io and time watchers get canceled whenever $w is destroyed, so keep a
25			copy
26
27			- timers can only be used once and must be recreated for repeated
28			operation
29	root	1.2
30			my $w = AnyEvent->condvar; # kind of main loop replacement
31	root	1.3	$w->wait; # enters main loop till $condvar gets ->broadcast
32			$w->broadcast; # wake up current and all future wait's
33
34			- condvars are used to give blocking behaviour when neccessary. Create a
35			condvar for any "request" or "event" your module might create,
36			"->broadcast" it when the event happens and provide a function that
37			calls "->wait" for it. See the examples below.
38	root	1.2
39			DESCRIPTION
40			AnyEvent provides an identical interface to multiple event loops. This
41			allows module authors to utilizy an event loop without forcing module
42			users to use the same event loop (as only a single event loop can
43			coexist peacefully at any one time).
44
45			The interface itself is vaguely similar but not identical to the Event
46			module.
47
48			On the first call of any method, the module tries to detect the
49			currently loaded event loop by probing wether any of the following
50			modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is
51			used. If none is found, the module tries to load these modules in the
52			order given. The first one that could be successfully loaded will be
53			used. If still none could be found, it will issue an error.
54
55			EXAMPLE
56			The following program uses an io watcher to read data from stdin, a
57			timer to display a message once per second, and a condvar to exit the
58			program when the user enters quit:
59
60			use AnyEvent;
61
62			my $cv = AnyEvent->condvar;
63
64			my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
65			warn "io event <$_[0]>\n"; # will always output <r>
66			chomp (my $input = <STDIN>); # read a line
67			warn "read: $input\n"; # output what has been read
68			$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
69			});
70
71			my $time_watcher; # can only be used once
72
73			sub new_timer {
74			$timer = AnyEvent->timer (after => 1, cb => sub {
75			warn "timeout\n"; # print 'timeout' about every second
76			&new_timer; # and restart the time
77			});
78			}
79
80			new_timer; # create first timer
81
82			$cv->wait; # wait until user enters /^q/i
83
84	root	1.3	REAL-WORLD EXAMPLE
85			Consider the Net::FCP module. It features (among others) the following
86			API calls, which are to freenet what HTTP GET requests are to http:
87
88			my $data = $fcp->client_get ($url); # blocks
89
90			my $transaction = $fcp->txn_client_get ($url); # does not block
91			$transaction->cb ( sub { ... } ); # set optional result callback
92			my $data = $transaction->result; # possibly blocks
93
94			The "client_get" method works like "LWP::Simple::get": it requests the
95			given URL and waits till the data has arrived. It is defined to be:
96
97			sub client_get { $_[0]->txn_client_get ($_[1])->result }
98
99			And in fact is automatically generated. This is the blocking API of
100			Net::FCP, and it works as simple as in any other, similar, module.
101
102			More complicated is "txn_client_get": It only creates a transaction
103			(completion, result, ...) object and initiates the transaction.
104
105			my $txn = bless { }, Net::FCP::Txn::;
106
107			It also creates a condition variable that is used to signal the
108			completion of the request:
109
110			$txn->{finished} = AnyAvent->condvar;
111
112			It then creates a socket in non-blocking mode.
113
114			socket $txn->{fh}, ...;
115			fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
116			connect $txn->{fh}, ...
117			and !$!{EWOULDBLOCK}
118			and !$!{EINPROGRESS}
119			and Carp::croak "unable to connect: $!\n";
120
121			Then it creates a write-watcher which gets called wehnever an error
122			occurs or the connection succeeds:
123
124			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
125
126			And returns this transaction object. The "fh_ready_w" callback gets
127			called as soon as the event loop detects that the socket is ready for
128			writing.
129
130			The "fh_ready_w" method makes the socket blocking again, writes the
131			request data and replaces the watcher by a read watcher (waiting for
132			reply data). The actual code is more complicated, but that doesn't
133			matter for this example:
134
135			fcntl $txn->{fh}, F_SETFL, 0;
136			syswrite $txn->{fh}, $txn->{request}
137			or die "connection or write error";
138			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
139
140			Again, "fh_ready_r" waits till all data has arrived, and then stores the
141			result and signals any possible waiters that the request ahs finished:
142
143			sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
144
145			if (end-of-file or data complete) {
146			$txn->{result} = $txn->{buf};
147			$txn->{finished}->broadcast;
148			}
149
150			The "result" method, finally, just waits for the finished signal (if the
151			request was already finished, it doesn't wait, of course, and returns
152			the data:
153
154			$txn->{finished}->wait;
155			return $txn->{buf};
156
157			The actual code goes further and collects all errors ("die"s,
158			exceptions) that occured during request processing. The "result" method
159			detects wether an exception as thrown (it is stored inside the $txn
160			object) and just throws the exception, which means connection errors and
161			other problems get reported tot he code that tries to use the result,
162			not in a random callback.
163
164			All of this enables the following usage styles:
165
166			1. Blocking:
167
168			my $data = $fcp->client_get ($url);
169
170			2. Blocking, but parallelizing:
171
172			my @datas = map $_->result,
173			map $fcp->txn_client_get ($_),
174			@urls;
175
176			Both blocking examples work without the module user having to know
177			anything about events.
178
179			3a. Event-based in a main program, using any support Event module:
180
181			use Event;
182
183			$fcp->txn_client_get ($url)->cb (sub {
184			my $txn = shift;
185			my $data = $txn->result;
186			...
187			});
188
189			Event::loop;
190
191			3b. The module user could use AnyEvent, too:
192
193			use AnyEvent;
194
195			my $quit = AnyEvent->condvar;
196
197			$fcp->txn_client_get ($url)->cb (sub {
198			...
199			$quit->broadcast;
200			});
201
202			$quit->wait;
203
204	root	1.2	SEE ALSO
205	root	1.3	Event modules: Coro::Event, Coro, Event, Glib::Event, Glib.
206
207			Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event,
208			AnyEvent::Impl::Glib, AnyEvent::Impl::Tk.
209
210			Nontrivial usage example: Net::FCP.
211	root	1.2
212