[ViewVC] Contents 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 (18 years, 5 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_3
Changes since 1.2:	+147 -12 lines
Log Message:	* empty log message *
#	Content
1	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	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {
10	my ($poll_got) = @_;
11	...
12	});
13
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	...
22	});
23
24	- 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
30	my $w = AnyEvent->condvar; # kind of main loop replacement
31	$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
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	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	SEE ALSO
205	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
212