Coro/Coro/AnyEvent.pm

=head1 NAME

Coro::AnyEvent - integrate threads into AnyEvent

=head1 SYNOPSIS

 use Coro;
 use AnyEvent;
 # using both Coro and AnyEvent will automatically load Coro::AnyEvent

 # or load it manually for its utility functions:
 use Coro::AnyEvent;

 Coro::AnyEvent::sleep 5;     # block current thread for 5s
 Coro::AnyEvent::poll;        # poll for new events once
 Coro::AnyEvent::idle;        # block until process no longer busy
 Coro::AnyEvent::idle_upto 5; # same, but only up to 5 seconds

 Coro::AnyEvent::readable $fh, 60
    or die "fh didn't become readable within 60 seconds\n";

=head1 DESCRIPTION

When one naively starts to use threads in Perl, one will quickly run
into the problem that threads which block on a syscall (sleeping,
reading from a socket etc.) will block all threads.

If one then uses an event loop, the problem is that the event loop has
no knowledge of threads and will not run them before it polls for new
events, again blocking the whole process.

This module integrates threads into any event loop supported by
AnyEvent, combining event-based programming with coroutine-based
programming in a natural way.

As of Coro 5.21 and newer, this module gets loaded automatically when
AnyEvent initialises itself and Coro is used in the same process, thus
there is no need to load it manually if you just want your threads to
coexist with AnyEvent.

If you want to use any functions from this module, you of course still
need to C<use Coro::AnyEvent>, just as with other perl modules.

Also, this module autodetects the event loop used (by relying on
L<AnyEvent>) and will either automatically defer to the high-performance
L<Coro::EV> or L<Coro::Event> modules, or will use a generic integration
method that should work with any event loop supported by L<AnyEvent>.

=head1 USAGE

=head2 RUN AN EVENT LOOP - OR NOT?

For performance reasons, it is recommended that the main program or
something else run the event loop of the event model you use, i.e.

   use Gtk2; # <- the event model
   use AnyEvent;
   use Coro:

   # initialise stuff
   async { ... };

   # now run mainloop of Gtk2
   main Gtk2;

You can move the event loop into a thread as well, although this tends to
get confusing:

   use Gtk2;
   use AnyEvent;
   use Coro:

   async { main Gtk2 };

   # do other things...
   while () {
      use Coro::AnyEvent;
      Coro::AnyEvent::sleep 1;
      print "ping...\n";
   }

You can also do nothing, in which case Coro::AnyEvent will invoke the event
loop as needed, which is less efficient, but sometimes very convenient.

What you I<MUST NOT EVER DO> is to block inside an event loop
callback. The reason is that most event loops are not reentrant and
this can cause a deadlock at best and corrupt memory at worst.

Coro will try to catch you when you block in the event loop
("FATAL: $Coro::IDLE blocked itself"), but this is just best effort and
only works when you do not run your own event loop.

To avoid this problem, start a new thread (e.g. with C<Coro::async_pool>)
or use C<Coro::unblock_sub> to run blocking tasks.

=head2 INVERSION OF CONTROL

If you need to wait for a single event, the rouse functions will come in
handy (see the Coro manpage for details):

   # wait for single SIGINT
   {
      my $int_w = AnyEvent->signal (signal => "INT", cb => Coro::rouse_cb);
      Coro::rouse_wait;
   }

=head2 EVENT MODULES OTHER THAN ANYEVENT

Keep in mind that, as shipped, Coro and Coro::AnyEvent only work with
AnyEvent, and only when AnyEvent is actually used (i.e. initialised), so
this will not work:

   # does not work: EV without AnyEvent is not recognised
   use EV;
   use Coro;

   EV::loop;

And neither does this, unless you actually I<use> AnyEvent for something:

   # does not work: AnyEvent must be initialised (e.g. by creating watchers)
   use EV;
   use AnyEvent;
   use Coro;

   EV::loop;

This does work, however, because you create a watcher (condvars work,
too), thus forcing AnyEvent to initialise itself:

   # does work: AnyEvent is actually used
   use EV;
   use AnyEvent;
   use Coro;

   my $timer = AE::timer 1, 1, sub { };

   EV::loop;

And if you want to use AnyEvent just to bridge between Coro and your event
model of choice, you can simply force it to initialise itself, like this:

   # does work: AnyEvent is initialised manually
   use POE;
   use AnyEvent;
   use Coro;

   AnyEvent::detect; # force AnyEvent to integrate Coro into POE
   POE::Kernel->run;

=head1 FUNCTIONS

Coro::AnyEvent also offers a few functions that might be useful.

=over 4

=cut

package Coro::AnyEvent;

use common::sense;

use Coro;
use AnyEvent ();

our $VERSION = 6.57;

#############################################################################
# idle handler

our $IDLE;

#############################################################################
# 0-timeout idle emulation watcher

our $ACTIVITY;

sub _activity {
   $ACTIVITY ||= AE::timer 0, 0, \&_schedule;
}

Coro::_set_readyhook (\&AnyEvent::detect);

AnyEvent::post_detect {
   my $model = $AnyEvent::MODEL;

   if ($model eq "AnyEvent::Impl::EV" and eval { require Coro::EV }) {
      # provide faster versions of some functions
      Coro::EV::_set_readyhook ();

      eval '
         *sleep = \&Coro::EV::timer_once;
         *poll  = \&Coro::EV::_poll;
         *idle  = sub() {
            my $w = EV::idle Coro::rouse_cb;
            Coro::rouse_wait;
         };
         *idle_upto = sub($) {
            my $cb = Coro::rouse_cb;
            my $t = EV::timer $_[0], 0, $cb;
            my $w = EV::idle $cb;
            Coro::rouse_wait;
         };
         *readable = sub($;$) {
            EV::READ  & Coro::EV::timed_io_once $_[0], EV::READ , $_[1]
         };
         *writable = sub($;$) {
            EV::WRITE & Coro::EV::timed_io_once $_[0], EV::WRITE, $_[1]
         };
      ';
      die if $@;

   } elsif ($model eq "AnyEvent::Impl::Event" and eval { require Coro::Event }) {
      Coro::_set_readyhook undef;
      # let Coro::Event do its thing
   } else {
      # do the inefficient thing ourselves
      Coro::_set_readyhook \&_activity;

      $IDLE = new Coro sub {
         my $_poll = AnyEvent->can ("_poll")
                  || AnyEvent->can ("one_event"); # AnyEvent < 6.0

         while () {
            $_poll->();
            Coro::schedule if Coro::nready;
         }
      };
      $IDLE->{desc} = "[AnyEvent idle process]";

      $Coro::idle = $IDLE;

      # call the readyhook, in case coroutines were already readied
      _activity;
   }

   # augment condvars
   unshift @AnyEvent::CondVar::ISA, "Coro::AnyEvent::CondVar";
};

=item Coro::AnyEvent::poll

This call will block the current thread until the event loop has polled
for potential new events and instructs the event loop to poll for new
events once, without blocking.

Note that this call will not actually execute the poll, nor will it wait
until there are some events, just block until the event loop has polled
for new events, so other threads will have a chance to run.

This is useful when you have a thread that does some computations, but you
still want to poll for new events from time to time. Simply call C<poll>
from time to time:

   my $long_calc = async {
      for (1..10000) {
         Coro::AnyEvent::poll;
         # do some stuff, make sure it takes at least 0.001s or so
      }
   }

Although you should also consider C<idle> or C<idle_upto> in such cases.

=item Coro::AnyEvent::sleep $seconds

This blocks the current thread for at least the given number of seconds.

=item Coro::AnyEvent::idle

This call is similar to C<poll> in that it will also poll for
events. Unlike C<poll>, it will only resume the thread once there are no
events to handle anymore, i.e. when the process is otherwise idle.

This is good for background threads that shouldn't use CPU time when
foreground jobs are ready to run.

=item Coro::AnyEvent::idle_upto $seconds

Like C<idle>, but with a maximum waiting time.

If your process is busy handling events, calling C<idle> can mean that
your thread will never be resumed. To avoid this, you can use C<idle_upto>
and specify a timeout, after which your thread will be resumed even if the
process is completely busy.

=item Coro::AnyEvent::readable $fh_or_fileno[, $timeout]

=item Coro::AnyEvent::writable $fh_or_fileno[, $timeout]

Blocks the current thread until the given file handle (or file descriptor)
becomes readable (or writable), or the given timeout has elapsed,
whichever happens first. No timeout counts as infinite timeout.

Returns true when the file handle became ready, false when a timeout
occurred.

Note that these functions are quite inefficient as compared to using a
single watcher (they recreate watchers on every invocation) or compared to
using Coro::Handle.

Note also that they only work for sources that have reasonable
non-blocking behaviour (e.g. not files).

Example: wait until STDIN becomes readable, then quit the program.

   use Coro::AnyEvent;
   print "press enter to quit...\n";
   Coro::AnyEvent::readable *STDIN;
   exit 0;

=cut

sub poll() {
   my $w = AE::timer 0, 0, Coro::rouse_cb;
   Coro::rouse_wait;
}

sub sleep($) {
   my $w = AE::timer $_[0], 0, Coro::rouse_cb;
   Coro::rouse_wait;
}

sub idle() {
   my $w = AE::idle Coro::rouse_cb;
   Coro::rouse_wait;
}

sub idle_upto($) {
   my $cb = Coro::rouse_cb;
   my $t = AE::timer shift, 0, $cb;
   my $w = AE::idle $cb;
   Coro::rouse_wait;
}

sub readable($;$) {
   my $cb = Coro::rouse_cb;
   my $w = AE::io $_[0], 0, sub { $cb->(1) };
   my $t = defined $_[1] && AE::timer $_[1], 0, sub { $cb->(0) };
   Coro::rouse_wait
}

sub writable($;$) {
   my $cb = Coro::rouse_cb;
   my $w = AE::io $_[0], 1, sub { $cb->(1) };
   my $t = defined $_[1] && AE::timer $_[1], 0, sub { $cb->(0) };
   Coro::rouse_wait
}

sub Coro::AnyEvent::CondVar::_send {
   (delete $_[0]{_ae_coro})->ready if $_[0]{_ae_coro};
};

sub Coro::AnyEvent::CondVar::_wait {
   until ($_[0]{_ae_sent}) {
      $AnyEvent::CondVar::Base::WAITING = 0; # avoid recursive check by AnyEvent
      local $_[0]{_ae_coro} = $Coro::current;
      Coro::schedule;
   }
};

1;

=back

=head1 IMPLEMENTATION DETAILS

Unfortunately, few event loops (basically only L<EV> and L<Event>)
support the kind of integration required for smooth operations well, and
consequently, AnyEvent cannot completely offer the functionality required
by this module, so we need to improvise.

Here is what this module does when it has to work with other event loops:

=over 4

=item * run ready threads before blocking the process

Each time a thread is put into the ready queue (and there are no other
threads in the ready queue), a timer with an C<after> value of C<0> is
registered with AnyEvent.

This creates something similar to an I<idle> watcher, i.e. a watcher
that keeps the event loop from blocking but still polls for new
events. (Unfortunately, some badly designed event loops (e.g. Event::Lib)
don't support a timeout of C<0> and will always block for a bit).

The callback for that timer will C<cede> to other threads of the same or
higher priority for as long as such threads exists. This has the effect of
running all threads that have work to do until all threads block to wait
for external events.

If no threads of equal or higher priority are ready, it will cede to any
thread, but only once. This has the effect of running lower-priority
threads as well, but it will not keep higher priority threads from
receiving new events.

The priority used is simply the priority of the thread that runs the event
loop, usually the main program, which usually has a priority of C<0>. Note
that Coro::AnyEvent does I<not> run an event loop for you, so unless the
main program runs one, there will simply be no event loop to C<cede> to
(event handling will still work, somewhat inefficiently, but any thread
will have a higher priority than event handling in that case).

=item * provide a suitable idle callback.

In addition to hooking into C<ready>, this module will also provide a
C<$Coro::idle> handler that runs the event loop. It is best not to take
advantage of this too often, as this is rather inefficient, but it should
work perfectly fine.

=item * provide overrides for AnyEvent's condvars

This module installs overrides for AnyEvent's condvars. That is, when
the module is loaded it will provide its own condition variables. This
makes them coroutine-safe, i.e. you can safely block on them from within a
coroutine.

=item * lead to data corruption or worse

As C<unblock_sub> cannot be used by this module (as it is the module
that implements it, basically), you must not call into the event
loop recursively from any coroutine. This is not usually a difficult
restriction to live with, just use condvars, C<unblock_sub> or other means
of inter-coroutine-communications.

If you use a module that supports AnyEvent (or uses the same event
loop as AnyEvent, making it implicitly compatible), and it offers
callbacks of any kind, then you must not block in them, either (or use
e.g. C<unblock_sub>), see the description of C<unblock_sub> in the
L<Coro> module.

This also means that you should load the module as early as possible,
as only condvars created after this module has been loaded will work
correctly.

=back

=head1 SEE ALSO

L<AnyEvent>, to see which event loops are supported, L<Coro::EV> and
L<Coro::Event> for more efficient and more correct solutions (they will be
used automatically if applicable).

=head1 AUTHOR/SUPPORT/CONTACT

   Marc A. Lehmann <schmorp@schmorp.de>
   http://software.schmorp.de/pkg/Coro.html

=cut

Revision:	1.119
Committed:	Sun Jul 26 10:30:56 2020 UTC (3 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-6_57, HEAD
Changes since 1.118:	+1 -0 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	Coro::AnyEvent - integrate threads into AnyEvent
4
5	=head1 SYNOPSIS
6
7	use Coro;
8	use AnyEvent;
9	# using both Coro and AnyEvent will automatically load Coro::AnyEvent
10
11	# or load it manually for its utility functions:
12	use Coro::AnyEvent;
13
14	Coro::AnyEvent::sleep 5; # block current thread for 5s
15	Coro::AnyEvent::poll; # poll for new events once
16	Coro::AnyEvent::idle; # block until process no longer busy
17	Coro::AnyEvent::idle_upto 5; # same, but only up to 5 seconds
18
19	Coro::AnyEvent::readable $fh, 60
20	or die "fh didn't become readable within 60 seconds\n";
21
22	=head1 DESCRIPTION
23
24	When one naively starts to use threads in Perl, one will quickly run
25	into the problem that threads which block on a syscall (sleeping,
26	reading from a socket etc.) will block all threads.
27
28	If one then uses an event loop, the problem is that the event loop has
29	no knowledge of threads and will not run them before it polls for new
30	events, again blocking the whole process.
31
32	This module integrates threads into any event loop supported by
33	AnyEvent, combining event-based programming with coroutine-based
34	programming in a natural way.
35
36	As of Coro 5.21 and newer, this module gets loaded automatically when
37	AnyEvent initialises itself and Coro is used in the same process, thus
38	there is no need to load it manually if you just want your threads to
39	coexist with AnyEvent.
40
41	If you want to use any functions from this module, you of course still
42	need to C<use Coro::AnyEvent>, just as with other perl modules.
43
44	Also, this module autodetects the event loop used (by relying on
45	L<AnyEvent>) and will either automatically defer to the high-performance
46	L<Coro::EV> or L<Coro::Event> modules, or will use a generic integration
47	method that should work with any event loop supported by L<AnyEvent>.
48
49	=head1 USAGE
50
51	=head2 RUN AN EVENT LOOP - OR NOT?
52
53	For performance reasons, it is recommended that the main program or
54	something else run the event loop of the event model you use, i.e.
55
56	use Gtk2; # <- the event model
57	use AnyEvent;
58	use Coro:
59
60	# initialise stuff
61	async { ... };
62
63	# now run mainloop of Gtk2
64	main Gtk2;
65
66	You can move the event loop into a thread as well, although this tends to
67	get confusing:
68
69	use Gtk2;
70	use AnyEvent;
71	use Coro:
72
73	async { main Gtk2 };
74
75	# do other things...
76	while () {
77	use Coro::AnyEvent;
78	Coro::AnyEvent::sleep 1;
79	print "ping...\n";
80	}
81
82	You can also do nothing, in which case Coro::AnyEvent will invoke the event
83	loop as needed, which is less efficient, but sometimes very convenient.
84
85	What you I<MUST NOT EVER DO> is to block inside an event loop
86	callback. The reason is that most event loops are not reentrant and
87	this can cause a deadlock at best and corrupt memory at worst.
88
89	Coro will try to catch you when you block in the event loop
90	("FATAL: $Coro::IDLE blocked itself"), but this is just best effort and
91	only works when you do not run your own event loop.
92
93	To avoid this problem, start a new thread (e.g. with C<Coro::async_pool>)
94	or use C<Coro::unblock_sub> to run blocking tasks.
95
96	=head2 INVERSION OF CONTROL
97
98	If you need to wait for a single event, the rouse functions will come in
99	handy (see the Coro manpage for details):
100
101	# wait for single SIGINT
102	{
103	my $int_w = AnyEvent->signal (signal => "INT", cb => Coro::rouse_cb);
104	Coro::rouse_wait;
105	}
106
107	=head2 EVENT MODULES OTHER THAN ANYEVENT
108
109	Keep in mind that, as shipped, Coro and Coro::AnyEvent only work with
110	AnyEvent, and only when AnyEvent is actually used (i.e. initialised), so
111	this will not work:
112
113	# does not work: EV without AnyEvent is not recognised
114	use EV;
115	use Coro;
116
117	EV::loop;
118
119	And neither does this, unless you actually I<use> AnyEvent for something:
120
121	# does not work: AnyEvent must be initialised (e.g. by creating watchers)
122	use EV;
123	use AnyEvent;
124	use Coro;
125
126	EV::loop;
127
128	This does work, however, because you create a watcher (condvars work,
129	too), thus forcing AnyEvent to initialise itself:
130
131	# does work: AnyEvent is actually used
132	use EV;
133	use AnyEvent;
134	use Coro;
135
136	my $timer = AE::timer 1, 1, sub { };
137
138	EV::loop;
139
140	And if you want to use AnyEvent just to bridge between Coro and your event
141	model of choice, you can simply force it to initialise itself, like this:
142
143	# does work: AnyEvent is initialised manually
144	use POE;
145	use AnyEvent;
146	use Coro;
147
148	AnyEvent::detect; # force AnyEvent to integrate Coro into POE
149	POE::Kernel->run;
150
151	=head1 FUNCTIONS
152
153	Coro::AnyEvent also offers a few functions that might be useful.
154
155	=over 4
156
157	=cut
158
159	package Coro::AnyEvent;
160
161	use common::sense;
162
163	use Coro;
164	use AnyEvent ();
165
166	our $VERSION = 6.57;
167
168	#############################################################################
169	# idle handler
170
171	our $IDLE;
172
173	#############################################################################
174	# 0-timeout idle emulation watcher
175
176	our $ACTIVITY;
177
178	sub _activity {
179	$ACTIVITY \|\|= AE::timer 0, 0, \&_schedule;
180	}
181
182	Coro::_set_readyhook (\&AnyEvent::detect);
183
184	AnyEvent::post_detect {
185	my $model = $AnyEvent::MODEL;
186
187	if ($model eq "AnyEvent::Impl::EV" and eval { require Coro::EV }) {
188	# provide faster versions of some functions
189	Coro::EV::_set_readyhook ();
190
191	eval '
192	*sleep = \&Coro::EV::timer_once;
193	*poll = \&Coro::EV::_poll;
194	*idle = sub() {
195	my $w = EV::idle Coro::rouse_cb;
196	Coro::rouse_wait;
197	};
198	*idle_upto = sub($) {
199	my $cb = Coro::rouse_cb;
200	my $t = EV::timer $_[0], 0, $cb;
201	my $w = EV::idle $cb;
202	Coro::rouse_wait;
203	};
204	*readable = sub($;$) {
205	EV::READ & Coro::EV::timed_io_once $_[0], EV::READ , $_[1]
206	};
207	*writable = sub($;$) {
208	EV::WRITE & Coro::EV::timed_io_once $_[0], EV::WRITE, $_[1]
209	};
210	';
211	die if $@;
212
213	} elsif ($model eq "AnyEvent::Impl::Event" and eval { require Coro::Event }) {
214	Coro::_set_readyhook undef;
215	# let Coro::Event do its thing
216	} else {
217	# do the inefficient thing ourselves
218	Coro::_set_readyhook \&_activity;
219
220	$IDLE = new Coro sub {
221	my $_poll = AnyEvent->can ("_poll")
222	\|\| AnyEvent->can ("one_event"); # AnyEvent < 6.0
223
224	while () {
225	$_poll->();
226	Coro::schedule if Coro::nready;
227	}
228	};
229	$IDLE->{desc} = "[AnyEvent idle process]";
230
231	$Coro::idle = $IDLE;
232
233	# call the readyhook, in case coroutines were already readied
234	_activity;
235	}
236
237	# augment condvars
238	unshift @AnyEvent::CondVar::ISA, "Coro::AnyEvent::CondVar";
239	};
240
241	=item Coro::AnyEvent::poll
242
243	This call will block the current thread until the event loop has polled
244	for potential new events and instructs the event loop to poll for new
245	events once, without blocking.
246
247	Note that this call will not actually execute the poll, nor will it wait
248	until there are some events, just block until the event loop has polled
249	for new events, so other threads will have a chance to run.
250
251	This is useful when you have a thread that does some computations, but you
252	still want to poll for new events from time to time. Simply call C<poll>
253	from time to time:
254
255	my $long_calc = async {
256	for (1..10000) {
257	Coro::AnyEvent::poll;
258	# do some stuff, make sure it takes at least 0.001s or so
259	}
260	}
261
262	Although you should also consider C<idle> or C<idle_upto> in such cases.
263
264	=item Coro::AnyEvent::sleep $seconds
265
266	This blocks the current thread for at least the given number of seconds.
267
268	=item Coro::AnyEvent::idle
269
270	This call is similar to C<poll> in that it will also poll for
271	events. Unlike C<poll>, it will only resume the thread once there are no
272	events to handle anymore, i.e. when the process is otherwise idle.
273
274	This is good for background threads that shouldn't use CPU time when
275	foreground jobs are ready to run.
276
277	=item Coro::AnyEvent::idle_upto $seconds
278
279	Like C<idle>, but with a maximum waiting time.
280
281	If your process is busy handling events, calling C<idle> can mean that
282	your thread will never be resumed. To avoid this, you can use C<idle_upto>
283	and specify a timeout, after which your thread will be resumed even if the
284	process is completely busy.
285
286	=item Coro::AnyEvent::readable $fh_or_fileno[, $timeout]
287
288	=item Coro::AnyEvent::writable $fh_or_fileno[, $timeout]
289
290	Blocks the current thread until the given file handle (or file descriptor)
291	becomes readable (or writable), or the given timeout has elapsed,
292	whichever happens first. No timeout counts as infinite timeout.
293
294	Returns true when the file handle became ready, false when a timeout
295	occurred.
296
297	Note that these functions are quite inefficient as compared to using a
298	single watcher (they recreate watchers on every invocation) or compared to
299	using Coro::Handle.
300
301	Note also that they only work for sources that have reasonable
302	non-blocking behaviour (e.g. not files).
303
304	Example: wait until STDIN becomes readable, then quit the program.
305
306	use Coro::AnyEvent;
307	print "press enter to quit...\n";
308	Coro::AnyEvent::readable *STDIN;
309	exit 0;
310
311	=cut
312
313	sub poll() {
314	my $w = AE::timer 0, 0, Coro::rouse_cb;
315	Coro::rouse_wait;
316	}
317
318	sub sleep($) {
319	my $w = AE::timer $_[0], 0, Coro::rouse_cb;
320	Coro::rouse_wait;
321	}
322
323	sub idle() {
324	my $w = AE::idle Coro::rouse_cb;
325	Coro::rouse_wait;
326	}
327
328	sub idle_upto($) {
329	my $cb = Coro::rouse_cb;
330	my $t = AE::timer shift, 0, $cb;
331	my $w = AE::idle $cb;
332	Coro::rouse_wait;
333	}
334
335	sub readable($;$) {
336	my $cb = Coro::rouse_cb;
337	my $w = AE::io $_[0], 0, sub { $cb->(1) };
338	my $t = defined $_[1] && AE::timer $_[1], 0, sub { $cb->(0) };
339	Coro::rouse_wait
340	}
341
342	sub writable($;$) {
343	my $cb = Coro::rouse_cb;
344	my $w = AE::io $_[0], 1, sub { $cb->(1) };
345	my $t = defined $_[1] && AE::timer $_[1], 0, sub { $cb->(0) };
346	Coro::rouse_wait
347	}
348
349	sub Coro::AnyEvent::CondVar::_send {
350	(delete $_[0]{_ae_coro})->ready if $_[0]{_ae_coro};
351	};
352
353	sub Coro::AnyEvent::CondVar::_wait {
354	until ($_[0]{_ae_sent}) {
355	$AnyEvent::CondVar::Base::WAITING = 0; # avoid recursive check by AnyEvent
356	local $_[0]{_ae_coro} = $Coro::current;
357	Coro::schedule;
358	}
359	};
360
361	1;
362
363	=back
364
365	=head1 IMPLEMENTATION DETAILS
366
367	Unfortunately, few event loops (basically only L<EV> and L<Event>)
368	support the kind of integration required for smooth operations well, and
369	consequently, AnyEvent cannot completely offer the functionality required
370	by this module, so we need to improvise.
371
372	Here is what this module does when it has to work with other event loops:
373
374	=over 4
375
376	=item * run ready threads before blocking the process
377
378	Each time a thread is put into the ready queue (and there are no other
379	threads in the ready queue), a timer with an C<after> value of C<0> is
380	registered with AnyEvent.
381
382	This creates something similar to an I<idle> watcher, i.e. a watcher
383	that keeps the event loop from blocking but still polls for new
384	events. (Unfortunately, some badly designed event loops (e.g. Event::Lib)
385	don't support a timeout of C<0> and will always block for a bit).
386
387	The callback for that timer will C<cede> to other threads of the same or
388	higher priority for as long as such threads exists. This has the effect of
389	running all threads that have work to do until all threads block to wait
390	for external events.
391
392	If no threads of equal or higher priority are ready, it will cede to any
393	thread, but only once. This has the effect of running lower-priority
394	threads as well, but it will not keep higher priority threads from
395	receiving new events.
396
397	The priority used is simply the priority of the thread that runs the event
398	loop, usually the main program, which usually has a priority of C<0>. Note
399	that Coro::AnyEvent does I<not> run an event loop for you, so unless the
400	main program runs one, there will simply be no event loop to C<cede> to
401	(event handling will still work, somewhat inefficiently, but any thread
402	will have a higher priority than event handling in that case).
403
404	=item * provide a suitable idle callback.
405
406	In addition to hooking into C<ready>, this module will also provide a
407	C<$Coro::idle> handler that runs the event loop. It is best not to take
408	advantage of this too often, as this is rather inefficient, but it should
409	work perfectly fine.
410
411	=item * provide overrides for AnyEvent's condvars
412
413	This module installs overrides for AnyEvent's condvars. That is, when
414	the module is loaded it will provide its own condition variables. This
415	makes them coroutine-safe, i.e. you can safely block on them from within a
416	coroutine.
417
418	=item * lead to data corruption or worse
419
420	As C<unblock_sub> cannot be used by this module (as it is the module
421	that implements it, basically), you must not call into the event
422	loop recursively from any coroutine. This is not usually a difficult
423	restriction to live with, just use condvars, C<unblock_sub> or other means
424	of inter-coroutine-communications.
425
426	If you use a module that supports AnyEvent (or uses the same event
427	loop as AnyEvent, making it implicitly compatible), and it offers
428	callbacks of any kind, then you must not block in them, either (or use
429	e.g. C<unblock_sub>), see the description of C<unblock_sub> in the
430	L<Coro> module.
431
432	This also means that you should load the module as early as possible,
433	as only condvars created after this module has been loaded will work
434	correctly.
435
436	=back
437
438	=head1 SEE ALSO
439
440	L<AnyEvent>, to see which event loops are supported, L<Coro::EV> and
441	L<Coro::Event> for more efficient and more correct solutions (they will be
442	used automatically if applicable).
443
444	=head1 AUTHOR/SUPPORT/CONTACT
445
446	Marc A. Lehmann <schmorp@schmorp.de>
447	http://software.schmorp.de/pkg/Coro.html
448
449	=cut
450