1 |
=head1 NAME |
2 |
|
3 |
Coro - the only real threads in perl |
4 |
|
5 |
=head1 SYNOPSIS |
6 |
|
7 |
use Coro; |
8 |
|
9 |
async { |
10 |
# some asynchronous thread of execution |
11 |
print "2\n"; |
12 |
cede; # yield back to main |
13 |
print "4\n"; |
14 |
}; |
15 |
print "1\n"; |
16 |
cede; # yield to coroutine |
17 |
print "3\n"; |
18 |
cede; # and again |
19 |
|
20 |
# use locking |
21 |
use Coro::Semaphore; |
22 |
my $lock = new Coro::Semaphore; |
23 |
my $locked; |
24 |
|
25 |
$lock->down; |
26 |
$locked = 1; |
27 |
$lock->up; |
28 |
|
29 |
=head1 DESCRIPTION |
30 |
|
31 |
For a tutorial-style introduction, please read the L<Coro::Intro> |
32 |
manpage. This manpage mainly contains reference information. |
33 |
|
34 |
This module collection manages continuations in general, most often |
35 |
in the form of cooperative threads (also called coroutines in the |
36 |
documentation). They are similar to kernel threads but don't (in general) |
37 |
run in parallel at the same time even on SMP machines. The specific flavor |
38 |
of thread offered by this module also guarantees you that it will not |
39 |
switch between threads unless necessary, at easily-identified points in |
40 |
your program, so locking and parallel access are rarely an issue, making |
41 |
thread programming much safer and easier than using other thread models. |
42 |
|
43 |
Unlike the so-called "Perl threads" (which are not actually real threads |
44 |
but only the windows process emulation ported to unix), Coro provides a |
45 |
full shared address space, which makes communication between threads |
46 |
very easy. And threads are fast, too: disabling the Windows process |
47 |
emulation code in your perl and using Coro can easily result in a two to |
48 |
four times speed increase for your programs. |
49 |
|
50 |
Coro achieves that by supporting multiple running interpreters that share |
51 |
data, which is especially useful to code pseudo-parallel processes and |
52 |
for event-based programming, such as multiple HTTP-GET requests running |
53 |
concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro |
54 |
into an event-based environment. |
55 |
|
56 |
In this module, a thread is defined as "callchain + lexical variables + |
57 |
@_ + $_ + $@ + $/ + C stack), that is, a thread has its own callchain, |
58 |
its own set of lexicals and its own set of perls most important global |
59 |
variables (see L<Coro::State> for more configuration and background info). |
60 |
|
61 |
See also the C<SEE ALSO> section at the end of this document - the Coro |
62 |
module family is quite large. |
63 |
|
64 |
=cut |
65 |
|
66 |
package Coro; |
67 |
|
68 |
use strict qw(vars subs); |
69 |
no warnings "uninitialized"; |
70 |
|
71 |
use Guard (); |
72 |
|
73 |
use Coro::State; |
74 |
|
75 |
use base qw(Coro::State Exporter); |
76 |
|
77 |
our $idle; # idle handler |
78 |
our $main; # main coroutine |
79 |
our $current; # current coroutine |
80 |
|
81 |
our $VERSION = 5.13; |
82 |
|
83 |
our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub); |
84 |
our %EXPORT_TAGS = ( |
85 |
prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)], |
86 |
); |
87 |
our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready)); |
88 |
|
89 |
=head1 GLOBAL VARIABLES |
90 |
|
91 |
=over 4 |
92 |
|
93 |
=item $Coro::main |
94 |
|
95 |
This variable stores the coroutine object that represents the main |
96 |
program. While you cna C<ready> it and do most other things you can do to |
97 |
coroutines, it is mainly useful to compare again C<$Coro::current>, to see |
98 |
whether you are running in the main program or not. |
99 |
|
100 |
=cut |
101 |
|
102 |
# $main is now being initialised by Coro::State |
103 |
|
104 |
=item $Coro::current |
105 |
|
106 |
The coroutine object representing the current coroutine (the last |
107 |
coroutine that the Coro scheduler switched to). The initial value is |
108 |
C<$Coro::main> (of course). |
109 |
|
110 |
This variable is B<strictly> I<read-only>. You can take copies of the |
111 |
value stored in it and use it as any other coroutine object, but you must |
112 |
not otherwise modify the variable itself. |
113 |
|
114 |
=cut |
115 |
|
116 |
sub current() { $current } # [DEPRECATED] |
117 |
|
118 |
=item $Coro::idle |
119 |
|
120 |
This variable is mainly useful to integrate Coro into event loops. It is |
121 |
usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is |
122 |
pretty low-level functionality. |
123 |
|
124 |
This variable stores either a coroutine or a callback. |
125 |
|
126 |
If it is a callback, the it is called whenever the scheduler finds no |
127 |
ready coroutines to run. The default implementation prints "FATAL: |
128 |
deadlock detected" and exits, because the program has no other way to |
129 |
continue. |
130 |
|
131 |
If it is a coroutine object, then this object will be readied (without |
132 |
invoking any ready hooks, however) when the scheduler finds no other ready |
133 |
coroutines to run. |
134 |
|
135 |
This hook is overwritten by modules such as C<Coro::EV> and |
136 |
C<Coro::AnyEvent> to wait on an external event that hopefully wake up a |
137 |
coroutine so the scheduler can run it. |
138 |
|
139 |
Note that the callback I<must not>, under any circumstances, block |
140 |
the current coroutine. Normally, this is achieved by having an "idle |
141 |
coroutine" that calls the event loop and then blocks again, and then |
142 |
readying that coroutine in the idle handler, or by simply placing the idle |
143 |
coroutine in this variable. |
144 |
|
145 |
See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this |
146 |
technique. |
147 |
|
148 |
Please note that if your callback recursively invokes perl (e.g. for event |
149 |
handlers), then it must be prepared to be called recursively itself. |
150 |
|
151 |
=cut |
152 |
|
153 |
$idle = sub { |
154 |
require Carp; |
155 |
Carp::croak ("FATAL: deadlock detected"); |
156 |
}; |
157 |
|
158 |
# this coroutine is necessary because a coroutine |
159 |
# cannot destroy itself. |
160 |
our @destroy; |
161 |
our $manager; |
162 |
|
163 |
$manager = new Coro sub { |
164 |
while () { |
165 |
Coro::_cancel shift @destroy |
166 |
while @destroy; |
167 |
|
168 |
&schedule; |
169 |
} |
170 |
}; |
171 |
$manager->{desc} = "[coro manager]"; |
172 |
$manager->prio (PRIO_MAX); |
173 |
|
174 |
=back |
175 |
|
176 |
=head1 SIMPLE COROUTINE CREATION |
177 |
|
178 |
=over 4 |
179 |
|
180 |
=item async { ... } [@args...] |
181 |
|
182 |
Create a new coroutine and return its coroutine object (usually |
183 |
unused). The coroutine will be put into the ready queue, so |
184 |
it will start running automatically on the next scheduler run. |
185 |
|
186 |
The first argument is a codeblock/closure that should be executed in the |
187 |
coroutine. When it returns argument returns the coroutine is automatically |
188 |
terminated. |
189 |
|
190 |
The remaining arguments are passed as arguments to the closure. |
191 |
|
192 |
See the C<Coro::State::new> constructor for info about the coroutine |
193 |
environment in which coroutines are executed. |
194 |
|
195 |
Calling C<exit> in a coroutine will do the same as calling exit outside |
196 |
the coroutine. Likewise, when the coroutine dies, the program will exit, |
197 |
just as it would in the main program. |
198 |
|
199 |
If you do not want that, you can provide a default C<die> handler, or |
200 |
simply avoid dieing (by use of C<eval>). |
201 |
|
202 |
Example: Create a new coroutine that just prints its arguments. |
203 |
|
204 |
async { |
205 |
print "@_\n"; |
206 |
} 1,2,3,4; |
207 |
|
208 |
=cut |
209 |
|
210 |
sub async(&@) { |
211 |
my $coro = new Coro @_; |
212 |
$coro->ready; |
213 |
$coro |
214 |
} |
215 |
|
216 |
=item async_pool { ... } [@args...] |
217 |
|
218 |
Similar to C<async>, but uses a coroutine pool, so you should not call |
219 |
terminate or join on it (although you are allowed to), and you get a |
220 |
coroutine that might have executed other code already (which can be good |
221 |
or bad :). |
222 |
|
223 |
On the plus side, this function is about twice as fast as creating (and |
224 |
destroying) a completely new coroutine, so if you need a lot of generic |
225 |
coroutines in quick successsion, use C<async_pool>, not C<async>. |
226 |
|
227 |
The code block is executed in an C<eval> context and a warning will be |
228 |
issued in case of an exception instead of terminating the program, as |
229 |
C<async> does. As the coroutine is being reused, stuff like C<on_destroy> |
230 |
will not work in the expected way, unless you call terminate or cancel, |
231 |
which somehow defeats the purpose of pooling (but is fine in the |
232 |
exceptional case). |
233 |
|
234 |
The priority will be reset to C<0> after each run, tracing will be |
235 |
disabled, the description will be reset and the default output filehandle |
236 |
gets restored, so you can change all these. Otherwise the coroutine will |
237 |
be re-used "as-is": most notably if you change other per-coroutine global |
238 |
stuff such as C<$/> you I<must needs> revert that change, which is most |
239 |
simply done by using local as in: C<< local $/ >>. |
240 |
|
241 |
The idle pool size is limited to C<8> idle coroutines (this can be |
242 |
adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle |
243 |
coros as required. |
244 |
|
245 |
If you are concerned about pooled coroutines growing a lot because a |
246 |
single C<async_pool> used a lot of stackspace you can e.g. C<async_pool |
247 |
{ terminate }> once per second or so to slowly replenish the pool. In |
248 |
addition to that, when the stacks used by a handler grows larger than 32kb |
249 |
(adjustable via $Coro::POOL_RSS) it will also be destroyed. |
250 |
|
251 |
=cut |
252 |
|
253 |
our $POOL_SIZE = 8; |
254 |
our $POOL_RSS = 32 * 1024; |
255 |
our @async_pool; |
256 |
|
257 |
sub pool_handler { |
258 |
while () { |
259 |
eval { |
260 |
&{&_pool_handler} while 1; |
261 |
}; |
262 |
|
263 |
warn $@ if $@; |
264 |
} |
265 |
} |
266 |
|
267 |
=back |
268 |
|
269 |
=head1 STATIC METHODS |
270 |
|
271 |
Static methods are actually functions that implicitly operate on the |
272 |
current coroutine. |
273 |
|
274 |
=over 4 |
275 |
|
276 |
=item schedule |
277 |
|
278 |
Calls the scheduler. The scheduler will find the next coroutine that is |
279 |
to be run from the ready queue and switches to it. The next coroutine |
280 |
to be run is simply the one with the highest priority that is longest |
281 |
in its ready queue. If there is no coroutine ready, it will clal the |
282 |
C<$Coro::idle> hook. |
283 |
|
284 |
Please note that the current coroutine will I<not> be put into the ready |
285 |
queue, so calling this function usually means you will never be called |
286 |
again unless something else (e.g. an event handler) calls C<< ->ready >>, |
287 |
thus waking you up. |
288 |
|
289 |
This makes C<schedule> I<the> generic method to use to block the current |
290 |
coroutine and wait for events: first you remember the current coroutine in |
291 |
a variable, then arrange for some callback of yours to call C<< ->ready |
292 |
>> on that once some event happens, and last you call C<schedule> to put |
293 |
yourself to sleep. Note that a lot of things can wake your coroutine up, |
294 |
so you need to check whether the event indeed happened, e.g. by storing the |
295 |
status in a variable. |
296 |
|
297 |
See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks. |
298 |
|
299 |
=item cede |
300 |
|
301 |
"Cede" to other coroutines. This function puts the current coroutine into |
302 |
the ready queue and calls C<schedule>, which has the effect of giving |
303 |
up the current "timeslice" to other coroutines of the same or higher |
304 |
priority. Once your coroutine gets its turn again it will automatically be |
305 |
resumed. |
306 |
|
307 |
This function is often called C<yield> in other languages. |
308 |
|
309 |
=item Coro::cede_notself |
310 |
|
311 |
Works like cede, but is not exported by default and will cede to I<any> |
312 |
coroutine, regardless of priority. This is useful sometimes to ensure |
313 |
progress is made. |
314 |
|
315 |
=item terminate [arg...] |
316 |
|
317 |
Terminates the current coroutine with the given status values (see L<cancel>). |
318 |
|
319 |
=item Coro::on_enter BLOCK, Coro::on_leave BLOCK |
320 |
|
321 |
These function install enter and leave winders in the current scope. The |
322 |
enter block will be executed when on_enter is called and whenever the |
323 |
current coroutine is re-entered by the scheduler, while the leave block is |
324 |
executed whenever the current coroutine is blocked by the scheduler, and |
325 |
also when the containing scope is exited (by whatever means, be it exit, |
326 |
die, last etc.). |
327 |
|
328 |
I<Neither invoking the scheduler, nor exceptions, are allowed within those |
329 |
BLOCKs>. That means: do not even think about calling C<die> without an |
330 |
eval, and do not even think of entering the scheduler in any way. |
331 |
|
332 |
Since both BLOCKs are tied to the current scope, they will automatically |
333 |
be removed when the current scope exits. |
334 |
|
335 |
These functions implement the same concept as C<dynamic-wind> in scheme |
336 |
does, and are useful when you want to localise some resource to a specific |
337 |
coroutine. |
338 |
|
339 |
They slow down coroutine switching considerably for coroutines that use |
340 |
them (But coroutine switching is still reasonably fast if the handlers are |
341 |
fast). |
342 |
|
343 |
These functions are best understood by an example: The following function |
344 |
will change the current timezone to "Antarctica/South_Pole", which |
345 |
requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>, |
346 |
which remember/change the current timezone and restore the previous |
347 |
value, respectively, the timezone is only changes for the coroutine that |
348 |
installed those handlers. |
349 |
|
350 |
use POSIX qw(tzset); |
351 |
|
352 |
async { |
353 |
my $old_tz; # store outside TZ value here |
354 |
|
355 |
Coro::on_enter { |
356 |
$old_tz = $ENV{TZ}; # remember the old value |
357 |
|
358 |
$ENV{TZ} = "Antarctica/South_Pole"; |
359 |
tzset; # enable new value |
360 |
}; |
361 |
|
362 |
Coro::on_leave { |
363 |
$ENV{TZ} = $old_tz; |
364 |
tzset; # restore old value |
365 |
}; |
366 |
|
367 |
# at this place, the timezone is Antarctica/South_Pole, |
368 |
# without disturbing the TZ of any other coroutine. |
369 |
}; |
370 |
|
371 |
This can be used to localise about any resource (locale, uid, current |
372 |
working directory etc.) to a block, despite the existance of other |
373 |
coroutines. |
374 |
|
375 |
=item killall |
376 |
|
377 |
Kills/terminates/cancels all coroutines except the currently running one. |
378 |
|
379 |
Note that while this will try to free some of the main interpreter |
380 |
resources if the calling coroutine isn't the main coroutine, but one |
381 |
cannot free all of them, so if a coroutine that is not the main coroutine |
382 |
calls this function, there will be some one-time resource leak. |
383 |
|
384 |
=cut |
385 |
|
386 |
sub killall { |
387 |
for (Coro::State::list) { |
388 |
$_->cancel |
389 |
if $_ != $current && UNIVERSAL::isa $_, "Coro"; |
390 |
} |
391 |
} |
392 |
|
393 |
=back |
394 |
|
395 |
=head1 COROUTINE OBJECT METHODS |
396 |
|
397 |
These are the methods you can call on coroutine objects (or to create |
398 |
them). |
399 |
|
400 |
=over 4 |
401 |
|
402 |
=item new Coro \&sub [, @args...] |
403 |
|
404 |
Create a new coroutine and return it. When the sub returns, the coroutine |
405 |
automatically terminates as if C<terminate> with the returned values were |
406 |
called. To make the coroutine run you must first put it into the ready |
407 |
queue by calling the ready method. |
408 |
|
409 |
See C<async> and C<Coro::State::new> for additional info about the |
410 |
coroutine environment. |
411 |
|
412 |
=cut |
413 |
|
414 |
sub _coro_run { |
415 |
terminate &{+shift}; |
416 |
} |
417 |
|
418 |
=item $success = $coroutine->ready |
419 |
|
420 |
Put the given coroutine into the end of its ready queue (there is one |
421 |
queue for each priority) and return true. If the coroutine is already in |
422 |
the ready queue, do nothing and return false. |
423 |
|
424 |
This ensures that the scheduler will resume this coroutine automatically |
425 |
once all the coroutines of higher priority and all coroutines of the same |
426 |
priority that were put into the ready queue earlier have been resumed. |
427 |
|
428 |
=item $is_ready = $coroutine->is_ready |
429 |
|
430 |
Return whether the coroutine is currently the ready queue or not, |
431 |
|
432 |
=item $coroutine->cancel (arg...) |
433 |
|
434 |
Terminates the given coroutine and makes it return the given arguments as |
435 |
status (default: the empty list). Never returns if the coroutine is the |
436 |
current coroutine. |
437 |
|
438 |
=cut |
439 |
|
440 |
sub cancel { |
441 |
my $self = shift; |
442 |
|
443 |
if ($current == $self) { |
444 |
terminate @_; |
445 |
} else { |
446 |
$self->{_status} = [@_]; |
447 |
$self->_cancel; |
448 |
} |
449 |
} |
450 |
|
451 |
=item $coroutine->schedule_to |
452 |
|
453 |
Puts the current coroutine to sleep (like C<Coro::schedule>), but instead |
454 |
of continuing with the next coro from the ready queue, always switch to |
455 |
the given coroutine object (regardless of priority etc.). The readyness |
456 |
state of that coroutine isn't changed. |
457 |
|
458 |
This is an advanced method for special cases - I'd love to hear about any |
459 |
uses for this one. |
460 |
|
461 |
=item $coroutine->cede_to |
462 |
|
463 |
Like C<schedule_to>, but puts the current coroutine into the ready |
464 |
queue. This has the effect of temporarily switching to the given |
465 |
coroutine, and continuing some time later. |
466 |
|
467 |
This is an advanced method for special cases - I'd love to hear about any |
468 |
uses for this one. |
469 |
|
470 |
=item $coroutine->throw ([$scalar]) |
471 |
|
472 |
If C<$throw> is specified and defined, it will be thrown as an exception |
473 |
inside the coroutine at the next convenient point in time. Otherwise |
474 |
clears the exception object. |
475 |
|
476 |
Coro will check for the exception each time a schedule-like-function |
477 |
returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down |
478 |
>>, C<< Coro::Handle->readable >> and so on. Most of these functions |
479 |
detect this case and return early in case an exception is pending. |
480 |
|
481 |
The exception object will be thrown "as is" with the specified scalar in |
482 |
C<$@>, i.e. if it is a string, no line number or newline will be appended |
483 |
(unlike with C<die>). |
484 |
|
485 |
This can be used as a softer means than C<cancel> to ask a coroutine to |
486 |
end itself, although there is no guarantee that the exception will lead to |
487 |
termination, and if the exception isn't caught it might well end the whole |
488 |
program. |
489 |
|
490 |
You might also think of C<throw> as being the moral equivalent of |
491 |
C<kill>ing a coroutine with a signal (in this case, a scalar). |
492 |
|
493 |
=item $coroutine->join |
494 |
|
495 |
Wait until the coroutine terminates and return any values given to the |
496 |
C<terminate> or C<cancel> functions. C<join> can be called concurrently |
497 |
from multiple coroutines, and all will be resumed and given the status |
498 |
return once the C<$coroutine> terminates. |
499 |
|
500 |
=cut |
501 |
|
502 |
sub join { |
503 |
my $self = shift; |
504 |
|
505 |
unless ($self->{_status}) { |
506 |
my $current = $current; |
507 |
|
508 |
push @{$self->{_on_destroy}}, sub { |
509 |
$current->ready; |
510 |
undef $current; |
511 |
}; |
512 |
|
513 |
&schedule while $current; |
514 |
} |
515 |
|
516 |
wantarray ? @{$self->{_status}} : $self->{_status}[0]; |
517 |
} |
518 |
|
519 |
=item $coroutine->on_destroy (\&cb) |
520 |
|
521 |
Registers a callback that is called when this coroutine gets destroyed, |
522 |
but before it is joined. The callback gets passed the terminate arguments, |
523 |
if any, and I<must not> die, under any circumstances. |
524 |
|
525 |
=cut |
526 |
|
527 |
sub on_destroy { |
528 |
my ($self, $cb) = @_; |
529 |
|
530 |
push @{ $self->{_on_destroy} }, $cb; |
531 |
} |
532 |
|
533 |
=item $oldprio = $coroutine->prio ($newprio) |
534 |
|
535 |
Sets (or gets, if the argument is missing) the priority of the |
536 |
coroutine. Higher priority coroutines get run before lower priority |
537 |
coroutines. Priorities are small signed integers (currently -4 .. +3), |
538 |
that you can refer to using PRIO_xxx constants (use the import tag :prio |
539 |
to get then): |
540 |
|
541 |
PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
542 |
3 > 1 > 0 > -1 > -3 > -4 |
543 |
|
544 |
# set priority to HIGH |
545 |
current->prio(PRIO_HIGH); |
546 |
|
547 |
The idle coroutine ($Coro::idle) always has a lower priority than any |
548 |
existing coroutine. |
549 |
|
550 |
Changing the priority of the current coroutine will take effect immediately, |
551 |
but changing the priority of coroutines in the ready queue (but not |
552 |
running) will only take effect after the next schedule (of that |
553 |
coroutine). This is a bug that will be fixed in some future version. |
554 |
|
555 |
=item $newprio = $coroutine->nice ($change) |
556 |
|
557 |
Similar to C<prio>, but subtract the given value from the priority (i.e. |
558 |
higher values mean lower priority, just as in unix). |
559 |
|
560 |
=item $olddesc = $coroutine->desc ($newdesc) |
561 |
|
562 |
Sets (or gets in case the argument is missing) the description for this |
563 |
coroutine. This is just a free-form string you can associate with a |
564 |
coroutine. |
565 |
|
566 |
This method simply sets the C<< $coroutine->{desc} >> member to the given |
567 |
string. You can modify this member directly if you wish. |
568 |
|
569 |
=cut |
570 |
|
571 |
sub desc { |
572 |
my $old = $_[0]{desc}; |
573 |
$_[0]{desc} = $_[1] if @_ > 1; |
574 |
$old; |
575 |
} |
576 |
|
577 |
sub transfer { |
578 |
require Carp; |
579 |
Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught"); |
580 |
} |
581 |
|
582 |
=back |
583 |
|
584 |
=head1 GLOBAL FUNCTIONS |
585 |
|
586 |
=over 4 |
587 |
|
588 |
=item Coro::nready |
589 |
|
590 |
Returns the number of coroutines that are currently in the ready state, |
591 |
i.e. that can be switched to by calling C<schedule> directory or |
592 |
indirectly. The value C<0> means that the only runnable coroutine is the |
593 |
currently running one, so C<cede> would have no effect, and C<schedule> |
594 |
would cause a deadlock unless there is an idle handler that wakes up some |
595 |
coroutines. |
596 |
|
597 |
=item my $guard = Coro::guard { ... } |
598 |
|
599 |
This function still exists, but is deprecated. Please use the |
600 |
C<Guard::guard> function instead. |
601 |
|
602 |
=cut |
603 |
|
604 |
BEGIN { *guard = \&Guard::guard } |
605 |
|
606 |
=item unblock_sub { ... } |
607 |
|
608 |
This utility function takes a BLOCK or code reference and "unblocks" it, |
609 |
returning a new coderef. Unblocking means that calling the new coderef |
610 |
will return immediately without blocking, returning nothing, while the |
611 |
original code ref will be called (with parameters) from within another |
612 |
coroutine. |
613 |
|
614 |
The reason this function exists is that many event libraries (such as the |
615 |
venerable L<Event|Event> module) are not coroutine-safe (a weaker form |
616 |
of reentrancy). This means you must not block within event callbacks, |
617 |
otherwise you might suffer from crashes or worse. The only event library |
618 |
currently known that is safe to use without C<unblock_sub> is L<EV>. |
619 |
|
620 |
This function allows your callbacks to block by executing them in another |
621 |
coroutine where it is safe to block. One example where blocking is handy |
622 |
is when you use the L<Coro::AIO|Coro::AIO> functions to save results to |
623 |
disk, for example. |
624 |
|
625 |
In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when |
626 |
creating event callbacks that want to block. |
627 |
|
628 |
If your handler does not plan to block (e.g. simply sends a message to |
629 |
another coroutine, or puts some other coroutine into the ready queue), |
630 |
there is no reason to use C<unblock_sub>. |
631 |
|
632 |
Note that you also need to use C<unblock_sub> for any other callbacks that |
633 |
are indirectly executed by any C-based event loop. For example, when you |
634 |
use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it |
635 |
provides callbacks that are the result of some event callback, then you |
636 |
must not block either, or use C<unblock_sub>. |
637 |
|
638 |
=cut |
639 |
|
640 |
our @unblock_queue; |
641 |
|
642 |
# we create a special coro because we want to cede, |
643 |
# to reduce pressure on the coro pool (because most callbacks |
644 |
# return immediately and can be reused) and because we cannot cede |
645 |
# inside an event callback. |
646 |
our $unblock_scheduler = new Coro sub { |
647 |
while () { |
648 |
while (my $cb = pop @unblock_queue) { |
649 |
&async_pool (@$cb); |
650 |
|
651 |
# for short-lived callbacks, this reduces pressure on the coro pool |
652 |
# as the chance is very high that the async_poll coro will be back |
653 |
# in the idle state when cede returns |
654 |
cede; |
655 |
} |
656 |
schedule; # sleep well |
657 |
} |
658 |
}; |
659 |
$unblock_scheduler->{desc} = "[unblock_sub scheduler]"; |
660 |
|
661 |
sub unblock_sub(&) { |
662 |
my $cb = shift; |
663 |
|
664 |
sub { |
665 |
unshift @unblock_queue, [$cb, @_]; |
666 |
$unblock_scheduler->ready; |
667 |
} |
668 |
} |
669 |
|
670 |
=item $cb = Coro::rouse_cb |
671 |
|
672 |
Create and return a "rouse callback". That's a code reference that, |
673 |
when called, will remember a copy of its arguments and notify the owner |
674 |
coroutine of the callback. |
675 |
|
676 |
See the next function. |
677 |
|
678 |
=item @args = Coro::rouse_wait [$cb] |
679 |
|
680 |
Wait for the specified rouse callback (or the last one that was created in |
681 |
this coroutine). |
682 |
|
683 |
As soon as the callback is invoked (or when the callback was invoked |
684 |
before C<rouse_wait>), it will return the arguments originally passed to |
685 |
the rouse callback. |
686 |
|
687 |
See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example. |
688 |
|
689 |
=back |
690 |
|
691 |
=cut |
692 |
|
693 |
1; |
694 |
|
695 |
=head1 HOW TO WAIT FOR A CALLBACK |
696 |
|
697 |
It is very common for a coroutine to wait for some callback to be |
698 |
called. This occurs naturally when you use coroutines in an otherwise |
699 |
event-based program, or when you use event-based libraries. |
700 |
|
701 |
These typically register a callback for some event, and call that callback |
702 |
when the event occured. In a coroutine, however, you typically want to |
703 |
just wait for the event, simplyifying things. |
704 |
|
705 |
For example C<< AnyEvent->child >> registers a callback to be called when |
706 |
a specific child has exited: |
707 |
|
708 |
my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... }); |
709 |
|
710 |
But from withina coroutine, you often just want to write this: |
711 |
|
712 |
my $status = wait_for_child $pid; |
713 |
|
714 |
Coro offers two functions specifically designed to make this easy, |
715 |
C<Coro::rouse_cb> and C<Coro::rouse_wait>. |
716 |
|
717 |
The first function, C<rouse_cb>, generates and returns a callback that, |
718 |
when invoked, will save its arguments and notify the coroutine that |
719 |
created the callback. |
720 |
|
721 |
The second function, C<rouse_wait>, waits for the callback to be called |
722 |
(by calling C<schedule> to go to sleep) and returns the arguments |
723 |
originally passed to the callback. |
724 |
|
725 |
Using these functions, it becomes easy to write the C<wait_for_child> |
726 |
function mentioned above: |
727 |
|
728 |
sub wait_for_child($) { |
729 |
my ($pid) = @_; |
730 |
|
731 |
my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb); |
732 |
|
733 |
my ($rpid, $rstatus) = Coro::rouse_wait; |
734 |
$rstatus |
735 |
} |
736 |
|
737 |
In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough, |
738 |
you can roll your own, using C<schedule>: |
739 |
|
740 |
sub wait_for_child($) { |
741 |
my ($pid) = @_; |
742 |
|
743 |
# store the current coroutine in $current, |
744 |
# and provide result variables for the closure passed to ->child |
745 |
my $current = $Coro::current; |
746 |
my ($done, $rstatus); |
747 |
|
748 |
# pass a closure to ->child |
749 |
my $watcher = AnyEvent->child (pid => $pid, cb => sub { |
750 |
$rstatus = $_[1]; # remember rstatus |
751 |
$done = 1; # mark $rstatus as valud |
752 |
}); |
753 |
|
754 |
# wait until the closure has been called |
755 |
schedule while !$done; |
756 |
|
757 |
$rstatus |
758 |
} |
759 |
|
760 |
|
761 |
=head1 BUGS/LIMITATIONS |
762 |
|
763 |
=over 4 |
764 |
|
765 |
=item fork with pthread backend |
766 |
|
767 |
When Coro is compiled using the pthread backend (which isn't recommended |
768 |
but required on many BSDs as their libcs are completely broken), then |
769 |
coroutines will not survive a fork. There is no known workaround except to |
770 |
fix your libc and use a saner backend. |
771 |
|
772 |
=item perl process emulation ("threads") |
773 |
|
774 |
This module is not perl-pseudo-thread-safe. You should only ever use this |
775 |
module from the first thread (this requirement might be removed in the |
776 |
future to allow per-thread schedulers, but Coro::State does not yet allow |
777 |
this). I recommend disabling thread support and using processes, as having |
778 |
the windows process emulation enabled under unix roughly halves perl |
779 |
performance, even when not used. |
780 |
|
781 |
=item coroutine switching not signal safe |
782 |
|
783 |
You must not switch to another coroutine from within a signal handler |
784 |
(only relevant with %SIG - most event libraries provide safe signals). |
785 |
|
786 |
That means you I<MUST NOT> call any function that might "block" the |
787 |
current coroutine - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or |
788 |
anything that calls those. Everything else, including calling C<ready>, |
789 |
works. |
790 |
|
791 |
=back |
792 |
|
793 |
|
794 |
=head1 SEE ALSO |
795 |
|
796 |
Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>. |
797 |
|
798 |
Debugging: L<Coro::Debug>. |
799 |
|
800 |
Support/Utility: L<Coro::Specific>, L<Coro::Util>. |
801 |
|
802 |
Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, |
803 |
L<Coro::SemaphoreSet>, L<Coro::RWLock>. |
804 |
|
805 |
I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>. |
806 |
|
807 |
Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for |
808 |
a better-working alternative), L<Coro::BDB>, L<Coro::Storable>, |
809 |
L<Coro::Select>. |
810 |
|
811 |
XS API: L<Coro::MakeMaker>. |
812 |
|
813 |
Low level Configuration, Thread Environment, Continuations: L<Coro::State>. |
814 |
|
815 |
=head1 AUTHOR |
816 |
|
817 |
Marc Lehmann <schmorp@schmorp.de> |
818 |
http://home.schmorp.de/ |
819 |
|
820 |
=cut |
821 |
|