1 |
=head1 NAME |
2 |
|
3 |
Coro - coroutine process abstraction |
4 |
|
5 |
=head1 SYNOPSIS |
6 |
|
7 |
use Coro; |
8 |
|
9 |
async { |
10 |
# some asynchronous thread of execution |
11 |
}; |
12 |
|
13 |
# alternatively create an async coroutine like this: |
14 |
|
15 |
sub some_func : Coro { |
16 |
# some more async code |
17 |
} |
18 |
|
19 |
cede; |
20 |
|
21 |
=head1 DESCRIPTION |
22 |
|
23 |
This module collection manages coroutines. Coroutines are similar |
24 |
to threads but don't run in parallel at the same time even on SMP |
25 |
machines. The specific flavor of coroutine used in this module also |
26 |
guarantees you that it will not switch between coroutines unless |
27 |
necessary, at easily-identified points in your program, so locking and |
28 |
parallel access are rarely an issue, making coroutine programming much |
29 |
safer than threads programming. |
30 |
|
31 |
(Perl, however, does not natively support real threads but instead does a |
32 |
very slow and memory-intensive emulation of processes using threads. This |
33 |
is a performance win on Windows machines, and a loss everywhere else). |
34 |
|
35 |
In this module, coroutines are defined as "callchain + lexical variables + |
36 |
@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain, |
37 |
its own set of lexicals and its own set of perls most important global |
38 |
variables. |
39 |
|
40 |
=cut |
41 |
|
42 |
package Coro; |
43 |
|
44 |
use strict; |
45 |
no warnings "uninitialized"; |
46 |
|
47 |
use Coro::State; |
48 |
|
49 |
use base qw(Coro::State Exporter); |
50 |
|
51 |
our $idle; # idle handler |
52 |
our $main; # main coroutine |
53 |
our $current; # current coroutine |
54 |
|
55 |
our $VERSION = '3.7'; |
56 |
|
57 |
our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub); |
58 |
our %EXPORT_TAGS = ( |
59 |
prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)], |
60 |
); |
61 |
our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready)); |
62 |
|
63 |
{ |
64 |
my @async; |
65 |
my $init; |
66 |
|
67 |
# this way of handling attributes simply is NOT scalable ;() |
68 |
sub import { |
69 |
no strict 'refs'; |
70 |
|
71 |
Coro->export_to_level (1, @_); |
72 |
|
73 |
my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE}; |
74 |
*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub { |
75 |
my ($package, $ref) = (shift, shift); |
76 |
my @attrs; |
77 |
for (@_) { |
78 |
if ($_ eq "Coro") { |
79 |
push @async, $ref; |
80 |
unless ($init++) { |
81 |
eval q{ |
82 |
sub INIT { |
83 |
&async(pop @async) while @async; |
84 |
} |
85 |
}; |
86 |
} |
87 |
} else { |
88 |
push @attrs, $_; |
89 |
} |
90 |
} |
91 |
return $old ? $old->($package, $ref, @attrs) : @attrs; |
92 |
}; |
93 |
} |
94 |
|
95 |
} |
96 |
|
97 |
=over 4 |
98 |
|
99 |
=item $main |
100 |
|
101 |
This coroutine represents the main program. |
102 |
|
103 |
=cut |
104 |
|
105 |
$main = new Coro; |
106 |
|
107 |
=item $current (or as function: current) |
108 |
|
109 |
The current coroutine (the last coroutine switched to). The initial value |
110 |
is C<$main> (of course). |
111 |
|
112 |
This variable is B<strictly> I<read-only>. It is provided for performance |
113 |
reasons. If performance is not essential you are encouraged to use the |
114 |
C<Coro::current> function instead. |
115 |
|
116 |
=cut |
117 |
|
118 |
# maybe some other module used Coro::Specific before... |
119 |
$main->{specific} = $current->{specific} |
120 |
if $current; |
121 |
|
122 |
_set_current $main; |
123 |
|
124 |
sub current() { $current } |
125 |
|
126 |
=item $idle |
127 |
|
128 |
A callback that is called whenever the scheduler finds no ready coroutines |
129 |
to run. The default implementation prints "FATAL: deadlock detected" and |
130 |
exits, because the program has no other way to continue. |
131 |
|
132 |
This hook is overwritten by modules such as C<Coro::Timer> and |
133 |
C<Coro::Event> to wait on an external event that hopefully wake up a |
134 |
coroutine so the scheduler can run it. |
135 |
|
136 |
Please note that if your callback recursively invokes perl (e.g. for event |
137 |
handlers), then it must be prepared to be called recursively. |
138 |
|
139 |
=cut |
140 |
|
141 |
$idle = sub { |
142 |
require Carp; |
143 |
Carp::croak ("FATAL: deadlock detected"); |
144 |
}; |
145 |
|
146 |
sub _cancel { |
147 |
my ($self) = @_; |
148 |
|
149 |
# free coroutine data and mark as destructed |
150 |
$self->_destroy |
151 |
or return; |
152 |
|
153 |
# call all destruction callbacks |
154 |
$_->(@{$self->{status}}) |
155 |
for @{(delete $self->{destroy_cb}) || []}; |
156 |
} |
157 |
|
158 |
# this coroutine is necessary because a coroutine |
159 |
# cannot destroy itself. |
160 |
my @destroy; |
161 |
my $manager; |
162 |
|
163 |
$manager = new Coro sub { |
164 |
$current->desc ("[coro manager]"); |
165 |
|
166 |
while () { |
167 |
(shift @destroy)->_cancel |
168 |
while @destroy; |
169 |
|
170 |
&schedule; |
171 |
} |
172 |
}; |
173 |
|
174 |
$manager->prio (PRIO_MAX); |
175 |
|
176 |
# static methods. not really. |
177 |
|
178 |
=back |
179 |
|
180 |
=head2 STATIC METHODS |
181 |
|
182 |
Static methods are actually functions that operate on the current coroutine only. |
183 |
|
184 |
=over 4 |
185 |
|
186 |
=item async { ... } [@args...] |
187 |
|
188 |
Create a new asynchronous coroutine and return it's coroutine object |
189 |
(usually unused). When the sub returns the new coroutine is automatically |
190 |
terminated. |
191 |
|
192 |
Calling C<exit> in a coroutine will do the same as calling exit outside |
193 |
the coroutine. Likewise, when the coroutine dies, the program will exit, |
194 |
just as it would in the main program. |
195 |
|
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# create a new coroutine that just prints its arguments |
197 |
async { |
198 |
print "@_\n"; |
199 |
} 1,2,3,4; |
200 |
|
201 |
=cut |
202 |
|
203 |
sub async(&@) { |
204 |
my $coro = new Coro @_; |
205 |
$coro->ready; |
206 |
$coro |
207 |
} |
208 |
|
209 |
=item async_pool { ... } [@args...] |
210 |
|
211 |
Similar to C<async>, but uses a coroutine pool, so you should not call |
212 |
terminate or join (although you are allowed to), and you get a coroutine |
213 |
that might have executed other code already (which can be good or bad :). |
214 |
|
215 |
Also, the block is executed in an C<eval> context and a warning will be |
216 |
issued in case of an exception instead of terminating the program, as |
217 |
C<async> does. As the coroutine is being reused, stuff like C<on_destroy> |
218 |
will not work in the expected way, unless you call terminate or cancel, |
219 |
which somehow defeats the purpose of pooling. |
220 |
|
221 |
The priority will be reset to C<0> after each job, otherwise the coroutine |
222 |
will be re-used "as-is". |
223 |
|
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The pool size is limited to 8 idle coroutines (this can be adjusted by |
225 |
changing $Coro::POOL_SIZE), and there can be as many non-idle coros as |
226 |
required. |
227 |
|
228 |
If you are concerned about pooled coroutines growing a lot because a |
229 |
single C<async_pool> used a lot of stackspace you can e.g. C<async_pool { |
230 |
terminate }> once per second or so to slowly replenish the pool. |
231 |
|
232 |
=cut |
233 |
|
234 |
our $POOL_SIZE = 8; |
235 |
our @pool; |
236 |
|
237 |
sub pool_handler { |
238 |
while () { |
239 |
$current->{desc} = "[async_pool]"; |
240 |
|
241 |
eval { |
242 |
my ($cb, @arg) = @{ delete $current->{_invoke} or return }; |
243 |
$cb->(@arg); |
244 |
}; |
245 |
warn $@ if $@; |
246 |
|
247 |
last if @pool >= $POOL_SIZE; |
248 |
|
249 |
push @pool, $current; |
250 |
$current->{desc} = "[async_pool idle]"; |
251 |
$current->save (Coro::State::SAVE_DEF); |
252 |
$current->prio (0); |
253 |
schedule; |
254 |
} |
255 |
} |
256 |
|
257 |
sub async_pool(&@) { |
258 |
# this is also inlined into the unlock_scheduler |
259 |
my $coro = (pop @pool) || new Coro \&pool_handler;; |
260 |
|
261 |
$coro->{_invoke} = [@_]; |
262 |
$coro->ready; |
263 |
|
264 |
$coro |
265 |
} |
266 |
|
267 |
=item schedule |
268 |
|
269 |
Calls the scheduler. Please note that the current coroutine will not be put |
270 |
into the ready queue, so calling this function usually means you will |
271 |
never be called again unless something else (e.g. an event handler) calls |
272 |
ready. |
273 |
|
274 |
The canonical way to wait on external events is this: |
275 |
|
276 |
{ |
277 |
# remember current coroutine |
278 |
my $current = $Coro::current; |
279 |
|
280 |
# register a hypothetical event handler |
281 |
on_event_invoke sub { |
282 |
# wake up sleeping coroutine |
283 |
$current->ready; |
284 |
undef $current; |
285 |
}; |
286 |
|
287 |
# call schedule until event occurred. |
288 |
# in case we are woken up for other reasons |
289 |
# (current still defined), loop. |
290 |
Coro::schedule while $current; |
291 |
} |
292 |
|
293 |
=item cede |
294 |
|
295 |
"Cede" to other coroutines. This function puts the current coroutine into the |
296 |
ready queue and calls C<schedule>, which has the effect of giving up the |
297 |
current "timeslice" to other coroutines of the same or higher priority. |
298 |
|
299 |
Returns true if at least one coroutine switch has happened. |
300 |
|
301 |
=item Coro::cede_notself |
302 |
|
303 |
Works like cede, but is not exported by default and will cede to any |
304 |
coroutine, regardless of priority, once. |
305 |
|
306 |
Returns true if at least one coroutine switch has happened. |
307 |
|
308 |
=item terminate [arg...] |
309 |
|
310 |
Terminates the current coroutine with the given status values (see L<cancel>). |
311 |
|
312 |
=cut |
313 |
|
314 |
sub terminate { |
315 |
$current->cancel (@_); |
316 |
} |
317 |
|
318 |
=back |
319 |
|
320 |
# dynamic methods |
321 |
|
322 |
=head2 COROUTINE METHODS |
323 |
|
324 |
These are the methods you can call on coroutine objects. |
325 |
|
326 |
=over 4 |
327 |
|
328 |
=item new Coro \&sub [, @args...] |
329 |
|
330 |
Create a new coroutine and return it. When the sub returns the coroutine |
331 |
automatically terminates as if C<terminate> with the returned values were |
332 |
called. To make the coroutine run you must first put it into the ready queue |
333 |
by calling the ready method. |
334 |
|
335 |
See C<async> for additional discussion. |
336 |
|
337 |
=cut |
338 |
|
339 |
sub _run_coro { |
340 |
terminate &{+shift}; |
341 |
} |
342 |
|
343 |
sub new { |
344 |
my $class = shift; |
345 |
|
346 |
$class->SUPER::new (\&_run_coro, @_) |
347 |
} |
348 |
|
349 |
=item $success = $coroutine->ready |
350 |
|
351 |
Put the given coroutine into the ready queue (according to it's priority) |
352 |
and return true. If the coroutine is already in the ready queue, do nothing |
353 |
and return false. |
354 |
|
355 |
=item $is_ready = $coroutine->is_ready |
356 |
|
357 |
Return wether the coroutine is currently the ready queue or not, |
358 |
|
359 |
=item $coroutine->cancel (arg...) |
360 |
|
361 |
Terminates the given coroutine and makes it return the given arguments as |
362 |
status (default: the empty list). Never returns if the coroutine is the |
363 |
current coroutine. |
364 |
|
365 |
=cut |
366 |
|
367 |
sub cancel { |
368 |
my $self = shift; |
369 |
$self->{status} = [@_]; |
370 |
|
371 |
if ($current == $self) { |
372 |
push @destroy, $self; |
373 |
$manager->ready; |
374 |
&schedule while 1; |
375 |
} else { |
376 |
$self->_cancel; |
377 |
} |
378 |
} |
379 |
|
380 |
=item $coroutine->join |
381 |
|
382 |
Wait until the coroutine terminates and return any values given to the |
383 |
C<terminate> or C<cancel> functions. C<join> can be called multiple times |
384 |
from multiple coroutine. |
385 |
|
386 |
=cut |
387 |
|
388 |
sub join { |
389 |
my $self = shift; |
390 |
|
391 |
unless ($self->{status}) { |
392 |
my $current = $current; |
393 |
|
394 |
push @{$self->{destroy_cb}}, sub { |
395 |
$current->ready; |
396 |
undef $current; |
397 |
}; |
398 |
|
399 |
&schedule while $current; |
400 |
} |
401 |
|
402 |
wantarray ? @{$self->{status}} : $self->{status}[0]; |
403 |
} |
404 |
|
405 |
=item $coroutine->on_destroy (\&cb) |
406 |
|
407 |
Registers a callback that is called when this coroutine gets destroyed, |
408 |
but before it is joined. The callback gets passed the terminate arguments, |
409 |
if any. |
410 |
|
411 |
=cut |
412 |
|
413 |
sub on_destroy { |
414 |
my ($self, $cb) = @_; |
415 |
|
416 |
push @{ $self->{destroy_cb} }, $cb; |
417 |
} |
418 |
|
419 |
=item $oldprio = $coroutine->prio ($newprio) |
420 |
|
421 |
Sets (or gets, if the argument is missing) the priority of the |
422 |
coroutine. Higher priority coroutines get run before lower priority |
423 |
coroutines. Priorities are small signed integers (currently -4 .. +3), |
424 |
that you can refer to using PRIO_xxx constants (use the import tag :prio |
425 |
to get then): |
426 |
|
427 |
PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
428 |
3 > 1 > 0 > -1 > -3 > -4 |
429 |
|
430 |
# set priority to HIGH |
431 |
current->prio(PRIO_HIGH); |
432 |
|
433 |
The idle coroutine ($Coro::idle) always has a lower priority than any |
434 |
existing coroutine. |
435 |
|
436 |
Changing the priority of the current coroutine will take effect immediately, |
437 |
but changing the priority of coroutines in the ready queue (but not |
438 |
running) will only take effect after the next schedule (of that |
439 |
coroutine). This is a bug that will be fixed in some future version. |
440 |
|
441 |
=item $newprio = $coroutine->nice ($change) |
442 |
|
443 |
Similar to C<prio>, but subtract the given value from the priority (i.e. |
444 |
higher values mean lower priority, just as in unix). |
445 |
|
446 |
=item $olddesc = $coroutine->desc ($newdesc) |
447 |
|
448 |
Sets (or gets in case the argument is missing) the description for this |
449 |
coroutine. This is just a free-form string you can associate with a coroutine. |
450 |
|
451 |
=cut |
452 |
|
453 |
sub desc { |
454 |
my $old = $_[0]{desc}; |
455 |
$_[0]{desc} = $_[1] if @_ > 1; |
456 |
$old; |
457 |
} |
458 |
|
459 |
=back |
460 |
|
461 |
=head2 GLOBAL FUNCTIONS |
462 |
|
463 |
=over 4 |
464 |
|
465 |
=item Coro::nready |
466 |
|
467 |
Returns the number of coroutines that are currently in the ready state, |
468 |
i.e. that can be switched to. The value C<0> means that the only runnable |
469 |
coroutine is the currently running one, so C<cede> would have no effect, |
470 |
and C<schedule> would cause a deadlock unless there is an idle handler |
471 |
that wakes up some coroutines. |
472 |
|
473 |
=item my $guard = Coro::guard { ... } |
474 |
|
475 |
This creates and returns a guard object. Nothing happens until the object |
476 |
gets destroyed, in which case the codeblock given as argument will be |
477 |
executed. This is useful to free locks or other resources in case of a |
478 |
runtime error or when the coroutine gets canceled, as in both cases the |
479 |
guard block will be executed. The guard object supports only one method, |
480 |
C<< ->cancel >>, which will keep the codeblock from being executed. |
481 |
|
482 |
Example: set some flag and clear it again when the coroutine gets canceled |
483 |
or the function returns: |
484 |
|
485 |
sub do_something { |
486 |
my $guard = Coro::guard { $busy = 0 }; |
487 |
$busy = 1; |
488 |
|
489 |
# do something that requires $busy to be true |
490 |
} |
491 |
|
492 |
=cut |
493 |
|
494 |
sub guard(&) { |
495 |
bless \(my $cb = $_[0]), "Coro::guard" |
496 |
} |
497 |
|
498 |
sub Coro::guard::cancel { |
499 |
${$_[0]} = sub { }; |
500 |
} |
501 |
|
502 |
sub Coro::guard::DESTROY { |
503 |
${$_[0]}->(); |
504 |
} |
505 |
|
506 |
|
507 |
=item unblock_sub { ... } |
508 |
|
509 |
This utility function takes a BLOCK or code reference and "unblocks" it, |
510 |
returning the new coderef. This means that the new coderef will return |
511 |
immediately without blocking, returning nothing, while the original code |
512 |
ref will be called (with parameters) from within its own coroutine. |
513 |
|
514 |
The reason this function exists is that many event libraries (such as the |
515 |
venerable L<Event|Event> module) are not coroutine-safe (a weaker form |
516 |
of thread-safety). This means you must not block within event callbacks, |
517 |
otherwise you might suffer from crashes or worse. |
518 |
|
519 |
This function allows your callbacks to block by executing them in another |
520 |
coroutine where it is safe to block. One example where blocking is handy |
521 |
is when you use the L<Coro::AIO|Coro::AIO> functions to save results to |
522 |
disk. |
523 |
|
524 |
In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when |
525 |
creating event callbacks that want to block. |
526 |
|
527 |
=cut |
528 |
|
529 |
our @unblock_queue; |
530 |
|
531 |
# we create a special coro because we want to cede, |
532 |
# to reduce pressure on the coro pool (because most callbacks |
533 |
# return immediately and can be reused) and because we cannot cede |
534 |
# inside an event callback. |
535 |
our $unblock_scheduler = async { |
536 |
$current->desc ("[unblock_sub scheduler]"); |
537 |
while () { |
538 |
while (my $cb = pop @unblock_queue) { |
539 |
# this is an inlined copy of async_pool |
540 |
my $coro = (pop @pool or new Coro \&pool_handler); |
541 |
|
542 |
$coro->{_invoke} = $cb; |
543 |
$coro->ready; |
544 |
cede; # for short-lived callbacks, this reduces pressure on the coro pool |
545 |
} |
546 |
schedule; # sleep well |
547 |
} |
548 |
}; |
549 |
|
550 |
sub unblock_sub(&) { |
551 |
my $cb = shift; |
552 |
|
553 |
sub { |
554 |
unshift @unblock_queue, [$cb, @_]; |
555 |
$unblock_scheduler->ready; |
556 |
} |
557 |
} |
558 |
|
559 |
=back |
560 |
|
561 |
=cut |
562 |
|
563 |
1; |
564 |
|
565 |
=head1 BUGS/LIMITATIONS |
566 |
|
567 |
- you must make very sure that no coro is still active on global |
568 |
destruction. very bad things might happen otherwise (usually segfaults). |
569 |
|
570 |
- this module is not thread-safe. You should only ever use this module |
571 |
from the same thread (this requirement might be loosened in the future |
572 |
to allow per-thread schedulers, but Coro::State does not yet allow |
573 |
this). |
574 |
|
575 |
=head1 SEE ALSO |
576 |
|
577 |
Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>. |
578 |
|
579 |
Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>. |
580 |
|
581 |
Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>. |
582 |
|
583 |
Embedding: L<Coro:MakeMaker> |
584 |
|
585 |
=head1 AUTHOR |
586 |
|
587 |
Marc Lehmann <schmorp@schmorp.de> |
588 |
http://home.schmorp.de/ |
589 |
|
590 |
=cut |
591 |
|