[ViewVC] Contents of: cvs/cvsroot/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.

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:	1.4
Committed:	Fri Dec 30 01:28:31 2005 UTC (20 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_4
Changes since 1.3:	+23 -10 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	(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
23	* AnyEvent will keep filehandles alive, so as long as the watcher
24	exists, the filehandle exists.
25
26	my $w = AnyEvent->timer (after => $seconds, cb => sub {
27	...
28	});
29
30	* io and time watchers get canceled whenever $w is destroyed, so keep a
31	copy
32
33	* timers can only be used once and must be recreated for repeated
34	operation (limitation by Glib and Tk).
35
36	my $w = AnyEvent->condvar; # kind of main loop replacement
37	$w->wait; # enters main loop till $condvar gets ->broadcast
38	$w->broadcast; # wake up current and all future wait's
39
40	* condvars are used to give blocking behaviour when neccessary. Create a
41	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
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	ENVIRONMENT VARIABLES
62	The following environment variables are used by this module:
63
64	"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event
65	model gets used.
66
67	EXAMPLE
68	The following program uses an io watcher to read data from stdin, a
69	timer to display a message once per second, and a condvar to exit the
70	program when the user enters quit:
71
72	use AnyEvent;
73
74	my $cv = AnyEvent->condvar;
75
76	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
77	warn "io event <$_[0]>\n"; # will always output <r>
78	chomp (my $input = <STDIN>); # read a line
79	warn "read: $input\n"; # output what has been read
80	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
81	});
82
83	my $time_watcher; # can only be used once
84
85	sub new_timer {
86	$timer = AnyEvent->timer (after => 1, cb => sub {
87	warn "timeout\n"; # print 'timeout' about every second
88	&new_timer; # and restart the time
89	});
90	}
91
92	new_timer; # create first timer
93
94	$cv->wait; # wait until user enters /^q/i
95
96	REAL-WORLD EXAMPLE
97	Consider the Net::FCP module. It features (among others) the following
98	API calls, which are to freenet what HTTP GET requests are to http:
99
100	my $data = $fcp->client_get ($url); # blocks
101
102	my $transaction = $fcp->txn_client_get ($url); # does not block
103	$transaction->cb ( sub { ... } ); # set optional result callback
104	my $data = $transaction->result; # possibly blocks
105
106	The "client_get" method works like "LWP::Simple::get": it requests the
107	given URL and waits till the data has arrived. It is defined to be:
108
109	sub client_get { $_[0]->txn_client_get ($_[1])->result }
110
111	And in fact is automatically generated. This is the blocking API of
112	Net::FCP, and it works as simple as in any other, similar, module.
113
114	More complicated is "txn_client_get": It only creates a transaction
115	(completion, result, ...) object and initiates the transaction.
116
117	my $txn = bless { }, Net::FCP::Txn::;
118
119	It also creates a condition variable that is used to signal the
120	completion of the request:
121
122	$txn->{finished} = AnyAvent->condvar;
123
124	It then creates a socket in non-blocking mode.
125
126	socket $txn->{fh}, ...;
127	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
128	connect $txn->{fh}, ...
129	and !$!{EWOULDBLOCK}
130	and !$!{EINPROGRESS}
131	and Carp::croak "unable to connect: $!\n";
132
133	Then it creates a write-watcher which gets called whenever an error
134	occurs or the connection succeeds:
135
136	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
137
138	And returns this transaction object. The "fh_ready_w" callback gets
139	called as soon as the event loop detects that the socket is ready for
140	writing.
141
142	The "fh_ready_w" method makes the socket blocking again, writes the
143	request data and replaces the watcher by a read watcher (waiting for
144	reply data). The actual code is more complicated, but that doesn't
145	matter for this example:
146
147	fcntl $txn->{fh}, F_SETFL, 0;
148	syswrite $txn->{fh}, $txn->{request}
149	or die "connection or write error";
150	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
151
152	Again, "fh_ready_r" waits till all data has arrived, and then stores the
153	result and signals any possible waiters that the request ahs finished:
154
155	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
156
157	if (end-of-file or data complete) {
158	$txn->{result} = $txn->{buf};
159	$txn->{finished}->broadcast;
160	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
161	}
162
163	The "result" method, finally, just waits for the finished signal (if the
164	request was already finished, it doesn't wait, of course, and returns
165	the data:
166
167	$txn->{finished}->wait;
168	return $txn->{result};
169
170	The actual code goes further and collects all errors ("die"s,
171	exceptions) that occured during request processing. The "result" method
172	detects wether an exception as thrown (it is stored inside the $txn
173	object) and just throws the exception, which means connection errors and
174	other problems get reported tot he code that tries to use the result,
175	not in a random callback.
176
177	All of this enables the following usage styles:
178
179	1. Blocking:
180
181	my $data = $fcp->client_get ($url);
182
183	2. Blocking, but parallelizing:
184
185	my @datas = map $_->result,
186	map $fcp->txn_client_get ($_),
187	@urls;
188
189	Both blocking examples work without the module user having to know
190	anything about events.
191
192	3a. Event-based in a main program, using any support Event module:
193
194	use Event;
195
196	$fcp->txn_client_get ($url)->cb (sub {
197	my $txn = shift;
198	my $data = $txn->result;
199	...
200	});
201
202	Event::loop;
203
204	3b. The module user could use AnyEvent, too:
205
206	use AnyEvent;
207
208	my $quit = AnyEvent->condvar;
209
210	$fcp->txn_client_get ($url)->cb (sub {
211	...
212	$quit->broadcast;
213	});
214
215	$quit->wait;
216
217	SEE ALSO
218	Event modules: Coro::Event, Coro, Event, Glib::Event, Glib.
219
220	Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event,
221	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk.
222
223	Nontrivial usage example: Net::FCP.
224
225