[ViewVC] Annotation of: cvs/AnyEvent/README

NAME
    AnyEvent - provide framework for multiple event loops

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

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

WHY YOU SHOULD USE THIS MODULE (OR NOT)
    Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
    nowadays. So what is different about AnyEvent?

    Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
    policy* and AnyEvent is *small and efficient*.

    First and foremost, *AnyEvent is not an event model* itself, it only
    interfaces to whatever event model the main program happens to use in a
    pragmatic way. For event models and certain classes of immortals alike,
    the statement "there can only be one" is a bitter reality, and AnyEvent
    helps hiding the differences.

    The goal of AnyEvent is to offer module authors the ability to do event
    programming (waiting for I/O or timer events) without subscribing to a
    religion, a way of living, and most importantly: without forcing your
    module users into the same thing by forcing them to use the same event
    model you use.

    For modules like POE or IO::Async (which is actually doing all I/O
    *synchronously*...), using them in your module is like joining a cult:
    After you joined, you are dependent on them and you cannot use anything
    else, as it is simply incompatible to everything that isn't itself.

    AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk
    works fine etc. etc. but none of these work together with the rest: POE
    + IO::Async? no go. Tk + Event? no go. If your module uses one of those,
    every user of your module has to use it, too. If your module uses
    AnyEvent, it works transparently with all event models it supports
    (including stuff like POE and IO::Async).

    In addition of being free of having to use *the one and only true event
    model*, AnyEvent also is free of bloat and policy: with POE or similar
    modules, you get an enourmous amount of code and strict rules you have
    to follow. AnyEvent, on the other hand, is lean and to the point by only
    offering the functionality that is useful, in as thin as a wrapper as
    technically possible.

    Of course, if you want lots of policy (this can arguably be somewhat
    useful) and you want to force your users to use the one and only event
    model, you should *not* use this module.

DESCRIPTION
    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: 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, 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
    "AnyEvent::Impl::Perl". Like other event modules you can load it
    explicitly.

WATCHERS
    AnyEvent has the central concept of a *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 "undef" or otherwise deleting all
    references to it).

    All watchers are created by calling a method on the "AnyEvent" class.

  IO WATCHERS
    You can create I/O watcher by calling the "AnyEvent->io" method with the
    following mandatory arguments:

    "fh" the Perl *filehandle* (not filedescriptor) to watch for events.
    "poll" must be a string that is either "r" or "w", that creates a
    watcher waiting for "r"eadable or "w"ritable events. "cb" the callback
    to invoke everytime the filehandle becomes ready.

    Only one io watcher per "fh" and "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;
       });

  TIME WATCHERS
    You can create a time watcher by calling the "AnyEvent->timer" method
    with the following mandatory arguments:

    "after" after how many seconds (fractions are supported) should the
    timer activate. "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;

  CONDITION WATCHERS
    Condition watchers can be created by calling the "AnyEvent->condvar"
    method without any arguments.

    A condition watcher watches for a condition - precisely that the
    "->broadcast" method has been called.

    Note that condition watchers recurse into the event loop - if you have
    two watchers that call "->wait" in a round-robbin fashion, you lose.
    Therefore, condition watchers are good to export to your caller, but you
    should avoid making a blocking wait, at least in callbacks, as this
    usually asks for trouble.

    The watcher has only two methods:

    $cv->wait
        Wait (blocking if necessary) until the "->broadcast" method has been
        called on c<$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.

    $cv->broadcast
        Flag the condition as ready - a running "->wait" and all further
        calls to "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;

  SIGNAL WATCHERS
    You can listen for signals using a signal watcher, "signal" is the
    signal *name* without any "SIG" prefix. Multiple signals events can be
    clumped together into one callback invocation, and callback invocation
    might or might not be asynchronous.

    These watchers might use %SIG, so programs overwriting those signals
    directly will likely not work correctly.

    Example: exit on SIGINT

       my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });

  CHILD PROCESS WATCHERS
    You can also listen for the status of a child process specified by the
    "pid" argument (or any child if the pid argument is 0). The watcher will
    trigger as often as status change for the child are received. This works
    by installing a signal handler for "SIGCHLD". The callback will be
    called with the pid and exit status (as returned by waitpid).

    Example: wait for pid 1333

      my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });

GLOBALS
    $AnyEvent::MODEL
        Contains "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 "AnyEvent::Impl:xxx" modules, but can be any other class in the
        case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).

        The known classes so far are:

           AnyEvent::Impl::CoroEV    based on Coro::EV, best choice.
           AnyEvent::Impl::EV        based on EV (an interface to libev, also best choice).
           AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
           AnyEvent::Impl::Event     based on Event, also second 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.

    AnyEvent::detect
        Returns $AnyEvent::MODEL, forcing autodetection of the event model
        if necessary. You should only call this function right before you
        would have created an AnyEvent watcher anyway, that is, very late at
        runtime.

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.

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 "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is
    generally better.

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
    @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::"
    package/class when it finds the "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 provide implementations for all watcher types (see
    AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code)
    and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to
    see the sources).

    The above isn't fictitious, the *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
    *rxvt-unicode*, and it is updated and maintained as part of the
    *rxvt-unicode* distribution.

    *rxvt-unicode* also cheats a bit by not providing blocking access to
    condition variables: code blocking while waiting for a condition will
    "die". This still works with most modules/usages, and blocking calls
    must not be in an interactive application, so it makes sense.

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:	1.14
Committed:	Mon Apr 7 19:46:50 2008 UTC (16 years, 1 month ago) by root
Branch:	MAIN
CVS Tags:	rel-3_0
Changes since 1.13:	+49 -1 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.2	NAME
2			AnyEvent - provide framework for multiple event loops
3
4	root	1.6	Event, Coro, Glib, Tk, Perl - various supported event loops
5	root	1.2
6			SYNOPSIS
7	root	1.4	use AnyEvent;
8	root	1.2
9	root	1.6	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
10	root	1.2	...
11			});
12	root	1.3
13			my $w = AnyEvent->timer (after => $seconds, cb => sub {
14	root	1.2	...
15			});
16
17	root	1.6	my $w = AnyEvent->condvar; # stores wether a condition was flagged
18			$w->wait; # enters "main loop" till $condvar gets ->broadcast
19	root	1.3	$w->broadcast; # wake up current and all future wait's
20
21	root	1.14	WHY YOU SHOULD USE THIS MODULE (OR NOT)
22			Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
23			nowadays. So what is different about AnyEvent?
24
25			Executive Summary: AnyEvent is compatible, AnyEvent is *free of
26			policy* and AnyEvent is small and efficient.
27
28			First and foremost, AnyEvent is not an event model itself, it only
29			interfaces to whatever event model the main program happens to use in a
30			pragmatic way. For event models and certain classes of immortals alike,
31			the statement "there can only be one" is a bitter reality, and AnyEvent
32			helps hiding the differences.
33
34			The goal of AnyEvent is to offer module authors the ability to do event
35			programming (waiting for I/O or timer events) without subscribing to a
36			religion, a way of living, and most importantly: without forcing your
37			module users into the same thing by forcing them to use the same event
38			model you use.
39
40			For modules like POE or IO::Async (which is actually doing all I/O
41			synchronously...), using them in your module is like joining a cult:
42			After you joined, you are dependent on them and you cannot use anything
43			else, as it is simply incompatible to everything that isn't itself.
44
45			AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk
46			works fine etc. etc. but none of these work together with the rest: POE
47			+ IO::Async? no go. Tk + Event? no go. If your module uses one of those,
48			every user of your module has to use it, too. If your module uses
49			AnyEvent, it works transparently with all event models it supports
50			(including stuff like POE and IO::Async).
51
52			In addition of being free of having to use *the one and only true event
53			model*, AnyEvent also is free of bloat and policy: with POE or similar
54			modules, you get an enourmous amount of code and strict rules you have
55			to follow. AnyEvent, on the other hand, is lean and to the point by only
56			offering the functionality that is useful, in as thin as a wrapper as
57			technically possible.
58
59			Of course, if you want lots of policy (this can arguably be somewhat
60			useful) and you want to force your users to use the one and only event
61			model, you should not use this module.
62
63	root	1.2	DESCRIPTION
64			AnyEvent provides an identical interface to multiple event loops. This
65	root	1.6	allows module authors to utilise an event loop without forcing module
66	root	1.2	users to use the same event loop (as only a single event loop can
67			coexist peacefully at any one time).
68
69			The interface itself is vaguely similar but not identical to the Event
70			module.
71
72			On the first call of any method, the module tries to detect the
73			currently loaded event loop by probing wether any of the following
74			modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is
75			used. If none is found, the module tries to load these modules in the
76			order given. The first one that could be successfully loaded will be
77	root	1.6	used. If still none could be found, AnyEvent will fall back to a
78			pure-perl event loop, which is also not very efficient.
79
80			Because AnyEvent first checks for modules that are already loaded,
81			loading an Event model explicitly before first using AnyEvent will
82			likely make that model the default. For example:
83
84			use Tk;
85			use AnyEvent;
86
87			# .. AnyEvent will likely default to Tk
88
89			The pure-perl implementation of AnyEvent is called
90			"AnyEvent::Impl::Perl". Like other event modules you can load it
91			explicitly.
92
93			WATCHERS
94			AnyEvent has the central concept of a watcher, which is an object that
95			stores relevant data for each kind of event you are waiting for, such as
96			the callback to call, the filehandle to watch, etc.
97
98			These watchers are normal Perl objects with normal Perl lifetime. After
99			creating a watcher it will immediately "watch" for events and invoke the
100			callback. To disable the watcher you have to destroy it (e.g. by setting
101			the variable that stores it to "undef" or otherwise deleting all
102			references to it).
103
104			All watchers are created by calling a method on the "AnyEvent" class.
105
106			IO WATCHERS
107			You can create I/O watcher by calling the "AnyEvent->io" method with the
108			following mandatory arguments:
109
110			"fh" the Perl filehandle (not filedescriptor) to watch for events.
111			"poll" must be a string that is either "r" or "w", that creates a
112	root	1.13	watcher waiting for "r"eadable or "w"ritable events. "cb" the callback
113	root	1.6	to invoke everytime the filehandle becomes ready.
114
115			Only one io watcher per "fh" and "poll" combination is allowed (i.e. on
116			a socket you can have one r + one w, not any more (limitation comes from
117			Tk - if you are sure you are not using Tk this limitation is gone).
118
119			Filehandles will be kept alive, so as long as the watcher exists, the
120			filehandle exists, too.
121
122			Example:
123
124			# wait for readability of STDIN, then read a line and disable the watcher
125			my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
126			chomp (my $input = <STDIN>);
127			warn "read: $input\n";
128			undef $w;
129			});
130
131	root	1.8	TIME WATCHERS
132			You can create a time watcher by calling the "AnyEvent->timer" method
133	root	1.6	with the following mandatory arguments:
134
135			"after" after how many seconds (fractions are supported) should the
136			timer activate. "cb" the callback to invoke.
137
138			The timer callback will be invoked at most once: if you want a repeating
139			timer you have to create a new watcher (this is a limitation by both Tk
140			and Glib).
141
142			Example:
143
144			# fire an event after 7.7 seconds
145			my $w = AnyEvent->timer (after => 7.7, cb => sub {
146			warn "timeout\n";
147			});
148
149			# to cancel the timer:
150	root	1.13	undef $w;
151	root	1.6
152			CONDITION WATCHERS
153			Condition watchers can be created by calling the "AnyEvent->condvar"
154			method without any arguments.
155
156			A condition watcher watches for a condition - precisely that the
157			"->broadcast" method has been called.
158
159	root	1.14	Note that condition watchers recurse into the event loop - if you have
160			two watchers that call "->wait" in a round-robbin fashion, you lose.
161			Therefore, condition watchers are good to export to your caller, but you
162			should avoid making a blocking wait, at least in callbacks, as this
163			usually asks for trouble.
164
165	root	1.6	The watcher has only two methods:
166
167			$cv->wait
168			Wait (blocking if necessary) until the "->broadcast" method has been
169			called on c<$cv>, while servicing other watchers normally.
170
171			Not all event models support a blocking wait - some die in that
172			case, so if you are using this from a module, never require a
173			blocking wait, but let the caller decide wether the call will block
174			or not (for example, by coupling condition variables with some kind
175			of request results and supporting callbacks so the caller knows that
176			getting the result will not block, while still suppporting blockign
177			waits if the caller so desires).
178
179			You can only wait once on a condition - additional calls will return
180			immediately.
181
182			$cv->broadcast
183			Flag the condition as ready - a running "->wait" and all further
184			calls to "wait" will return after this method has been called. If
185			nobody is waiting the broadcast will be remembered..
186
187			Example:
188
189			# wait till the result is ready
190			my $result_ready = AnyEvent->condvar;
191
192			# do something such as adding a timer
193			# or socket watcher the calls $result_ready->broadcast
194			# when the "result" is ready.
195
196			$result_ready->wait;
197
198	root	1.8	SIGNAL WATCHERS
199			You can listen for signals using a signal watcher, "signal" is the
200			signal name without any "SIG" prefix. Multiple signals events can be
201	root	1.9	clumped together into one callback invocation, and callback invocation
202	root	1.8	might or might not be asynchronous.
203
204			These watchers might use %SIG, so programs overwriting those signals
205			directly will likely not work correctly.
206
207			Example: exit on SIGINT
208
209			my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
210
211			CHILD PROCESS WATCHERS
212			You can also listen for the status of a child process specified by the
213	root	1.11	"pid" argument (or any child if the pid argument is 0). The watcher will
214			trigger as often as status change for the child are received. This works
215			by installing a signal handler for "SIGCHLD". The callback will be
216			called with the pid and exit status (as returned by waitpid).
217	root	1.8
218			Example: wait for pid 1333
219
220			my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
221
222	root	1.7	GLOBALS
223			$AnyEvent::MODEL
224			Contains "undef" until the first watcher is being created. Then it
225			contains the event model that is being used, which is the name of
226			the Perl class implementing the model. This class is usually one of
227			the "AnyEvent::Impl:xxx" modules, but can be any other class in the
228			case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
229
230			The known classes so far are:
231
232	root	1.12	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
233			AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).
234	root	1.14	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
235	root	1.11	AnyEvent::Impl::Event based on Event, also second best choice :)
236	root	1.7	AnyEvent::Impl::Glib based on Glib, second-best choice.
237			AnyEvent::Impl::Tk based on Tk, very bad choice.
238			AnyEvent::Impl::Perl pure-perl implementation, inefficient.
239
240	root	1.8	AnyEvent::detect
241			Returns $AnyEvent::MODEL, forcing autodetection of the event model
242			if necessary. You should only call this function right before you
243			would have created an AnyEvent watcher anyway, that is, very late at
244			runtime.
245
246	root	1.6	WHAT TO DO IN A MODULE
247			As a module author, you should "use AnyEvent" and call AnyEvent methods
248			freely, but you should not load a specific event module or rely on it.
249
250			Be careful when you create watchers in the module body - Anyevent will
251			decide which event module to use as soon as the first method is called,
252			so by calling AnyEvent in your module body you force the user of your
253			module to load the event module first.
254
255			WHAT TO DO IN THE MAIN PROGRAM
256			There will always be a single main program - the only place that should
257			dictate which event model to use.
258
259			If it doesn't care, it can just "use AnyEvent" and use it itself, or not
260			do anything special and let AnyEvent decide which implementation to
261			chose.
262
263			If the main program relies on a specific event model (for example, in
264			Gtk2 programs you have to rely on either Glib or Glib::Event), you
265			should load it before loading AnyEvent or any module that uses it,
266			generally, as early as possible. The reason is that modules might create
267			watchers when they are loaded, and AnyEvent will decide on the event
268			model to use as soon as it creates watchers, and it might chose the
269			wrong one unless you load the correct one yourself.
270
271			You can chose to use a rather inefficient pure-perl implementation by
272			loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is
273			generally better.
274	root	1.2
275	root	1.5	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
276			If you need to support another event library which isn't directly
277			supported by AnyEvent, you can supply your own interface to it by
278	root	1.6	pushing, before the first watcher gets created, the package name of the
279	root	1.5	event module and the package name of the interface to use onto
280			@AnyEvent::REGISTRY. You can do that before and even without loading
281			AnyEvent.
282
283			Example:
284
285			push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
286
287	root	1.6	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
288			package/class when it finds the "urxvt" package/module is loaded. When
289			AnyEvent is loaded and asked to find a suitable event model, it will
290			first check for the presence of urxvt.
291
292	root	1.8	The class should provide implementations for all watcher types (see
293	root	1.6	AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code)
294			and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to
295			see the sources).
296	root	1.5
297			The above isn't fictitious, the rxvt-unicode (a.k.a. urxvt) uses the
298	root	1.6	above line as-is. An interface isn't included in AnyEvent because it
299	root	1.5	doesn't make sense outside the embedded interpreter inside
300			rxvt-unicode, and it is updated and maintained as part of the
301			rxvt-unicode distribution.
302
303	root	1.6	rxvt-unicode also cheats a bit by not providing blocking access to
304			condition variables: code blocking while waiting for a condition will
305			"die". This still works with most modules/usages, and blocking calls
306	root	1.10	must not be in an interactive application, so it makes sense.
307	root	1.6
308	root	1.4	ENVIRONMENT VARIABLES
309			The following environment variables are used by this module:
310
311			"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event
312			model gets used.
313
314	root	1.2	EXAMPLE
315			The following program uses an io watcher to read data from stdin, a
316			timer to display a message once per second, and a condvar to exit the
317			program when the user enters quit:
318
319			use AnyEvent;
320
321			my $cv = AnyEvent->condvar;
322
323			my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
324			warn "io event <$_[0]>\n"; # will always output <r>
325			chomp (my $input = <STDIN>); # read a line
326			warn "read: $input\n"; # output what has been read
327			$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
328			});
329
330			my $time_watcher; # can only be used once
331
332			sub new_timer {
333			$timer = AnyEvent->timer (after => 1, cb => sub {
334			warn "timeout\n"; # print 'timeout' about every second
335			&new_timer; # and restart the time
336			});
337			}
338
339			new_timer; # create first timer
340
341			$cv->wait; # wait until user enters /^q/i
342
343	root	1.3	REAL-WORLD EXAMPLE
344			Consider the Net::FCP module. It features (among others) the following
345			API calls, which are to freenet what HTTP GET requests are to http:
346
347			my $data = $fcp->client_get ($url); # blocks
348
349			my $transaction = $fcp->txn_client_get ($url); # does not block
350			$transaction->cb ( sub { ... } ); # set optional result callback
351			my $data = $transaction->result; # possibly blocks
352
353			The "client_get" method works like "LWP::Simple::get": it requests the
354			given URL and waits till the data has arrived. It is defined to be:
355
356			sub client_get { $_[0]->txn_client_get ($_[1])->result }
357
358			And in fact is automatically generated. This is the blocking API of
359			Net::FCP, and it works as simple as in any other, similar, module.
360
361			More complicated is "txn_client_get": It only creates a transaction
362			(completion, result, ...) object and initiates the transaction.
363
364			my $txn = bless { }, Net::FCP::Txn::;
365
366			It also creates a condition variable that is used to signal the
367			completion of the request:
368
369			$txn->{finished} = AnyAvent->condvar;
370
371			It then creates a socket in non-blocking mode.
372
373			socket $txn->{fh}, ...;
374			fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
375			connect $txn->{fh}, ...
376			and !$!{EWOULDBLOCK}
377			and !$!{EINPROGRESS}
378			and Carp::croak "unable to connect: $!\n";
379
380	root	1.4	Then it creates a write-watcher which gets called whenever an error
381	root	1.3	occurs or the connection succeeds:
382
383			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
384
385			And returns this transaction object. The "fh_ready_w" callback gets
386			called as soon as the event loop detects that the socket is ready for
387			writing.
388
389			The "fh_ready_w" method makes the socket blocking again, writes the
390			request data and replaces the watcher by a read watcher (waiting for
391			reply data). The actual code is more complicated, but that doesn't
392			matter for this example:
393
394			fcntl $txn->{fh}, F_SETFL, 0;
395			syswrite $txn->{fh}, $txn->{request}
396			or die "connection or write error";
397			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
398
399			Again, "fh_ready_r" waits till all data has arrived, and then stores the
400			result and signals any possible waiters that the request ahs finished:
401
402			sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
403
404			if (end-of-file or data complete) {
405			$txn->{result} = $txn->{buf};
406			$txn->{finished}->broadcast;
407	root	1.4	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
408	root	1.3	}
409
410			The "result" method, finally, just waits for the finished signal (if the
411			request was already finished, it doesn't wait, of course, and returns
412			the data:
413
414			$txn->{finished}->wait;
415	root	1.4	return $txn->{result};
416	root	1.3
417			The actual code goes further and collects all errors ("die"s,
418			exceptions) that occured during request processing. The "result" method
419			detects wether an exception as thrown (it is stored inside the $txn
420			object) and just throws the exception, which means connection errors and
421			other problems get reported tot he code that tries to use the result,
422			not in a random callback.
423
424			All of this enables the following usage styles:
425
426			1. Blocking:
427
428			my $data = $fcp->client_get ($url);
429
430			2. Blocking, but parallelizing:
431
432			my @datas = map $_->result,
433			map $fcp->txn_client_get ($_),
434			@urls;
435
436			Both blocking examples work without the module user having to know
437			anything about events.
438
439			3a. Event-based in a main program, using any support Event module:
440
441			use Event;
442
443			$fcp->txn_client_get ($url)->cb (sub {
444			my $txn = shift;
445			my $data = $txn->result;
446			...
447			});
448
449			Event::loop;
450
451			3b. The module user could use AnyEvent, too:
452
453			use AnyEvent;
454
455			my $quit = AnyEvent->condvar;
456
457			$fcp->txn_client_get ($url)->cb (sub {
458			...
459			$quit->broadcast;
460			});
461
462			$quit->wait;
463
464	root	1.2	SEE ALSO
465	root	1.3	Event modules: Coro::Event, Coro, Event, Glib::Event, Glib.
466
467			Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event,
468			AnyEvent::Impl::Glib, AnyEvent::Impl::Tk.
469
470			Nontrivial usage example: Net::FCP.
471	root	1.2
472