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1=head1 NAME 1=head1 NAME
2 2
3Coro - create and manage simple coroutines 3Coro - coroutine process abstraction
4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use Coro; 7 use Coro;
8 8
9 $new = new Coro sub { 9 async {
10 print "in coroutine, switching back\n"; 10 # some asynchronous thread of execution
11 $new->transfer($main); 11 print "2\n";
12 print "in coroutine again, switching back\n"; 12 cede; # yield back to main
13 $new->transfer($main); 13 print "4\n";
14 }; 14 };
15 15 print "1\n";
16 $main = new Coro; 16 cede; # yield to coroutine
17 17 print "3\n";
18 print "in main, switching to coroutine\n"; 18 cede; # and again
19 $main->transfer($new); 19
20 print "back in main, switch to coroutine again\n"; 20 # use locking
21 $main->transfer($new); 21 use Coro::Semaphore;
22 print "back in main\n"; 22 my $lock = new Coro::Semaphore;
23 my $locked;
24
25 $lock->down;
26 $locked = 1;
27 $lock->up;
23 28
24=head1 DESCRIPTION 29=head1 DESCRIPTION
25 30
26This module implements coroutines. Coroutines, similar to continuations, 31This module collection manages coroutines. Coroutines are similar to
27allow you to run more than one "thread of execution" in parallel. Unlike 32threads but don't (in general) run in parallel at the same time even
28threads this, only voluntary switching is used so locking problems are 33on SMP machines. The specific flavor of coroutine used in this module
29greatly reduced. 34also guarantees you that it will not switch between coroutines unless
35necessary, at easily-identified points in your program, so locking and
36parallel access are rarely an issue, making coroutine programming much
37safer and easier than threads programming.
30 38
31Although this is the "main" module of the Coro family it provides only 39Unlike a normal perl program, however, coroutines allow you to have
32low-level functionality. See L<Coro::Process> and related modules for a 40multiple running interpreters that share data, which is especially useful
33more useful process abstraction including scheduling. 41to code pseudo-parallel processes and for event-based programming, such as
42multiple HTTP-GET requests running concurrently. See L<Coro::AnyEvent> to
43learn more.
44
45Coroutines are also useful because Perl has no support for threads (the so
46called "threads" that perl offers are nothing more than the (bad) process
47emulation coming from the Windows platform: On standard operating systems
48they serve no purpose whatsoever, except by making your programs slow and
49making them use a lot of memory. Best disable them when building perl, or
50aks your software vendor/distributor to do it for you).
51
52In this module, coroutines are defined as "callchain + lexical variables +
53@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
54its own set of lexicals and its own set of perls most important global
55variables (see L<Coro::State> for more configuration).
56
57=cut
58
59package Coro;
60
61use strict;
62no warnings "uninitialized";
63
64use Coro::State;
65
66use base qw(Coro::State Exporter);
67
68our $idle; # idle handler
69our $main; # main coroutine
70our $current; # current coroutine
71
72our $VERSION = 4.746;
73
74our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
75our %EXPORT_TAGS = (
76 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
77);
78our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
34 79
35=over 4 80=over 4
36 81
37=cut 82=item $Coro::main
38 83
39package Coro; 84This variable stores the coroutine object that represents the main
85program. While you cna C<ready> it and do most other things you can do to
86coroutines, it is mainly useful to compare again C<$Coro::current>, to see
87whether you are running in the main program or not.
40 88
41BEGIN { 89=cut
42 $VERSION = 0.03;
43 90
91$main = new Coro;
92
93=item $Coro::current
94
95The coroutine object representing the current coroutine (the last
96coroutine that the Coro scheduler switched to). The initial value is
97C<$main> (of course).
98
99This variable is B<strictly> I<read-only>. You can take copies of the
100value stored in it and use it as any other coroutine object, but you must
101not otherwise modify the variable itself.
102
103=cut
104
105$main->{desc} = "[main::]";
106
107# maybe some other module used Coro::Specific before...
108$main->{_specific} = $current->{_specific}
109 if $current;
110
111_set_current $main;
112
113sub current() { $current } # [DEPRECATED]
114
115=item $Coro::idle
116
117This variable is mainly useful to integrate Coro into event loops. It is
118usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is
119pretty low-level functionality.
120
121This variable stores a callback that is called whenever the scheduler
122finds no ready coroutines to run. The default implementation prints
123"FATAL: deadlock detected" and exits, because the program has no other way
124to continue.
125
126This hook is overwritten by modules such as C<Coro::Timer> and
127C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
128coroutine so the scheduler can run it.
129
130Note that the callback I<must not>, under any circumstances, block
131the current coroutine. Normally, this is achieved by having an "idle
132coroutine" that calls the event loop and then blocks again, and then
133readying that coroutine in the idle handler.
134
135See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
136technique.
137
138Please note that if your callback recursively invokes perl (e.g. for event
139handlers), then it must be prepared to be called recursively itself.
140
141=cut
142
143$idle = sub {
44 require XSLoader; 144 require Carp;
45 XSLoader::load Coro, $VERSION; 145 Carp::croak ("FATAL: deadlock detected");
46} 146};
47 147
48=item $coro = new [$coderef [, @args]] 148sub _cancel {
149 my ($self) = @_;
49 150
50Create a new coroutine and return it. The first C<transfer> call to this 151 # free coroutine data and mark as destructed
51coroutine will start execution at the given coderef. If, the subroutine 152 $self->_destroy
52returns it will be executed again. 153 or return;
53 154
54If the coderef is omitted this function will create a new "empty" 155 # call all destruction callbacks
55coroutine, i.e. a coroutine that cannot be transfered to but can be used 156 $_->(@{$self->{_status}})
56to save the current coroutine in. 157 for @{(delete $self->{_on_destroy}) || []};
158}
57 159
160# this coroutine is necessary because a coroutine
161# cannot destroy itself.
162my @destroy;
163my $manager;
164
165$manager = new Coro sub {
166 while () {
167 (shift @destroy)->_cancel
168 while @destroy;
169
170 &schedule;
171 }
172};
173$manager->desc ("[coro manager]");
174$manager->prio (PRIO_MAX);
175
176=back
177
178=head2 SIMPLE COROUTINE CREATION
179
180=over 4
181
182=item async { ... } [@args...]
183
184Create a new coroutine and return it's coroutine object (usually
185unused). The coroutine will be put into the ready queue, so
186it will start running automatically on the next scheduler run.
187
188The first argument is a codeblock/closure that should be executed in the
189coroutine. When it returns argument returns the coroutine is automatically
190terminated.
191
192The remaining arguments are passed as arguments to the closure.
193
194See the C<Coro::State::new> constructor for info about the coroutine
195environment in which coroutines are executed.
196
197Calling C<exit> in a coroutine will do the same as calling exit outside
198the coroutine. Likewise, when the coroutine dies, the program will exit,
199just as it would in the main program.
200
201If you do not want that, you can provide a default C<die> handler, or
202simply avoid dieing (by use of C<eval>).
203
204Example: Create a new coroutine that just prints its arguments.
205
206 async {
207 print "@_\n";
208 } 1,2,3,4;
209
58=cut 210=cut
211
212sub async(&@) {
213 my $coro = new Coro @_;
214 $coro->ready;
215 $coro
216}
217
218=item async_pool { ... } [@args...]
219
220Similar to C<async>, but uses a coroutine pool, so you should not call
221terminate or join on it (although you are allowed to), and you get a
222coroutine that might have executed other code already (which can be good
223or bad :).
224
225On the plus side, this function is faster than creating (and destroying)
226a completely new coroutine, so if you need a lot of generic coroutines in
227quick successsion, use C<async_pool>, not C<async>.
228
229The code block is executed in an C<eval> context and a warning will be
230issued in case of an exception instead of terminating the program, as
231C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
232will not work in the expected way, unless you call terminate or cancel,
233which somehow defeats the purpose of pooling (but is fine in the
234exceptional case).
235
236The priority will be reset to C<0> after each run, tracing will be
237disabled, the description will be reset and the default output filehandle
238gets restored, so you can change all these. Otherwise the coroutine will
239be re-used "as-is": most notably if you change other per-coroutine global
240stuff such as C<$/> you I<must needs> to revert that change, which is most
241simply done by using local as in: C< local $/ >.
242
243The pool size is limited to C<8> idle coroutines (this can be adjusted by
244changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
245required.
246
247If you are concerned about pooled coroutines growing a lot because a
248single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
249{ terminate }> once per second or so to slowly replenish the pool. In
250addition to that, when the stacks used by a handler grows larger than 16kb
251(adjustable via $Coro::POOL_RSS) it will also be destroyed.
252
253=cut
254
255our $POOL_SIZE = 8;
256our $POOL_RSS = 16 * 1024;
257our @async_pool;
258
259sub pool_handler {
260 my $cb;
261
262 while () {
263 eval {
264 while () {
265 _pool_1 $cb;
266 &$cb;
267 _pool_2 $cb;
268 &schedule;
269 }
270 };
271
272 if ($@) {
273 last if $@ eq "\3async_pool terminate\2\n";
274 warn $@;
275 }
276 }
277}
278
279sub async_pool(&@) {
280 # this is also inlined into the unlock_scheduler
281 my $coro = (pop @async_pool) || new Coro \&pool_handler;
282
283 $coro->{_invoke} = [@_];
284 $coro->ready;
285
286 $coro
287}
288
289=back
290
291=head2 STATIC METHODS
292
293Static methods are actually functions that operate on the current coroutine.
294
295=over 4
296
297=item schedule
298
299Calls the scheduler. The scheduler will find the next coroutine that is
300to be run from the ready queue and switches to it. The next coroutine
301to be run is simply the one with the highest priority that is longest
302in its ready queue. If there is no coroutine ready, it will clal the
303C<$Coro::idle> hook.
304
305Please note that the current coroutine will I<not> be put into the ready
306queue, so calling this function usually means you will never be called
307again unless something else (e.g. an event handler) calls C<< ->ready >>,
308thus waking you up.
309
310This makes C<schedule> I<the> generic method to use to block the current
311coroutine and wait for events: first you remember the current coroutine in
312a variable, then arrange for some callback of yours to call C<< ->ready
313>> on that once some event happens, and last you call C<schedule> to put
314yourself to sleep. Note that a lot of things can wake your coroutine up,
315so you need to check whether the event indeed happened, e.g. by storing the
316status in a variable.
317
318The canonical way to wait on external events is this:
319
320 {
321 # remember current coroutine
322 my $current = $Coro::current;
323
324 # register a hypothetical event handler
325 on_event_invoke sub {
326 # wake up sleeping coroutine
327 $current->ready;
328 undef $current;
329 };
330
331 # call schedule until event occurred.
332 # in case we are woken up for other reasons
333 # (current still defined), loop.
334 Coro::schedule while $current;
335 }
336
337=item cede
338
339"Cede" to other coroutines. This function puts the current coroutine into
340the ready queue and calls C<schedule>, which has the effect of giving
341up the current "timeslice" to other coroutines of the same or higher
342priority. Once your coroutine gets its turn again it will automatically be
343resumed.
344
345This function is often called C<yield> in other languages.
346
347=item Coro::cede_notself
348
349Works like cede, but is not exported by default and will cede to I<any>
350coroutine, regardless of priority. This is useful sometimes to ensure
351progress is made.
352
353=item terminate [arg...]
354
355Terminates the current coroutine with the given status values (see L<cancel>).
356
357=item killall
358
359Kills/terminates/cancels all coroutines except the currently running
360one. This is useful after a fork, either in the child or the parent, as
361usually only one of them should inherit the running coroutines.
362
363Note that while this will try to free some of the main programs resources,
364you cannot free all of them, so if a coroutine that is not the main
365program calls this function, there will be some one-time resource leak.
366
367=cut
368
369sub terminate {
370 $current->cancel (@_);
371}
372
373sub killall {
374 for (Coro::State::list) {
375 $_->cancel
376 if $_ != $current && UNIVERSAL::isa $_, "Coro";
377 }
378}
379
380=back
381
382=head2 COROUTINE METHODS
383
384These are the methods you can call on coroutine objects (or to create
385them).
386
387=over 4
388
389=item new Coro \&sub [, @args...]
390
391Create a new coroutine and return it. When the sub returns, the coroutine
392automatically terminates as if C<terminate> with the returned values were
393called. To make the coroutine run you must first put it into the ready
394queue by calling the ready method.
395
396See C<async> and C<Coro::State::new> for additional info about the
397coroutine environment.
398
399=cut
400
401sub _run_coro {
402 terminate &{+shift};
403}
59 404
60sub new { 405sub new {
61 my $class = $_[0]; 406 my $class = shift;
62 my $proc = $_[1] || sub { die "tried to transfer to an empty coroutine" }; 407
63 bless _newprocess { 408 $class->SUPER::new (\&_run_coro, @_)
64 do { 409}
65 eval { &$proc }; 410
66 if ($@) { 411=item $success = $coroutine->ready
67 $error_msg = $@; 412
68 $error_coro = _newprocess { }; 413Put the given coroutine into the end of its ready queue (there is one
69 &transfer($error_coro, $error); 414queue for each priority) and return true. If the coroutine is already in
415the ready queue, do nothing and return false.
416
417This ensures that the scheduler will resume this coroutine automatically
418once all the coroutines of higher priority and all coroutines of the same
419priority that were put into the ready queue earlier have been resumed.
420
421=item $is_ready = $coroutine->is_ready
422
423Return whether the coroutine is currently the ready queue or not,
424
425=item $coroutine->cancel (arg...)
426
427Terminates the given coroutine and makes it return the given arguments as
428status (default: the empty list). Never returns if the coroutine is the
429current coroutine.
430
431=cut
432
433sub cancel {
434 my $self = shift;
435 $self->{_status} = [@_];
436
437 if ($current == $self) {
438 push @destroy, $self;
439 $manager->ready;
440 &schedule while 1;
441 } else {
442 $self->_cancel;
443 }
444}
445
446=item $coroutine->join
447
448Wait until the coroutine terminates and return any values given to the
449C<terminate> or C<cancel> functions. C<join> can be called concurrently
450from multiple coroutines, and all will be resumed and given the status
451return once the C<$coroutine> terminates.
452
453=cut
454
455sub join {
456 my $self = shift;
457
458 unless ($self->{_status}) {
459 my $current = $current;
460
461 push @{$self->{_on_destroy}}, sub {
462 $current->ready;
463 undef $current;
464 };
465
466 &schedule while $current;
467 }
468
469 wantarray ? @{$self->{_status}} : $self->{_status}[0];
470}
471
472=item $coroutine->on_destroy (\&cb)
473
474Registers a callback that is called when this coroutine gets destroyed,
475but before it is joined. The callback gets passed the terminate arguments,
476if any, and I<must not> die, under any circumstances.
477
478=cut
479
480sub on_destroy {
481 my ($self, $cb) = @_;
482
483 push @{ $self->{_on_destroy} }, $cb;
484}
485
486=item $oldprio = $coroutine->prio ($newprio)
487
488Sets (or gets, if the argument is missing) the priority of the
489coroutine. Higher priority coroutines get run before lower priority
490coroutines. Priorities are small signed integers (currently -4 .. +3),
491that you can refer to using PRIO_xxx constants (use the import tag :prio
492to get then):
493
494 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
495 3 > 1 > 0 > -1 > -3 > -4
496
497 # set priority to HIGH
498 current->prio(PRIO_HIGH);
499
500The idle coroutine ($Coro::idle) always has a lower priority than any
501existing coroutine.
502
503Changing the priority of the current coroutine will take effect immediately,
504but changing the priority of coroutines in the ready queue (but not
505running) will only take effect after the next schedule (of that
506coroutine). This is a bug that will be fixed in some future version.
507
508=item $newprio = $coroutine->nice ($change)
509
510Similar to C<prio>, but subtract the given value from the priority (i.e.
511higher values mean lower priority, just as in unix).
512
513=item $olddesc = $coroutine->desc ($newdesc)
514
515Sets (or gets in case the argument is missing) the description for this
516coroutine. This is just a free-form string you can associate with a coroutine.
517
518This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
519can modify this member directly if you wish.
520
521=item $coroutine->throw ([$scalar])
522
523If C<$throw> is specified and defined, it will be thrown as an exception
524inside the coroutine at the next convinient point in time (usually after
525it gains control at the next schedule/transfer/cede). Otherwise clears the
526exception object.
527
528The exception object will be thrown "as is" with the specified scalar in
529C<$@>, i.e. if it is a string, no line number or newline will be appended
530(unlike with C<die>).
531
532This can be used as a softer means than C<cancel> to ask a coroutine to
533end itself, although there is no guarentee that the exception will lead to
534termination, and if the exception isn't caught it might well end the whole
535program.
536
537=cut
538
539sub desc {
540 my $old = $_[0]{desc};
541 $_[0]{desc} = $_[1] if @_ > 1;
542 $old;
543}
544
545=back
546
547=head2 GLOBAL FUNCTIONS
548
549=over 4
550
551=item Coro::nready
552
553Returns the number of coroutines that are currently in the ready state,
554i.e. that can be switched to by calling C<schedule> directory or
555indirectly. The value C<0> means that the only runnable coroutine is the
556currently running one, so C<cede> would have no effect, and C<schedule>
557would cause a deadlock unless there is an idle handler that wakes up some
558coroutines.
559
560=item my $guard = Coro::guard { ... }
561
562This creates and returns a guard object. Nothing happens until the object
563gets destroyed, in which case the codeblock given as argument will be
564executed. This is useful to free locks or other resources in case of a
565runtime error or when the coroutine gets canceled, as in both cases the
566guard block will be executed. The guard object supports only one method,
567C<< ->cancel >>, which will keep the codeblock from being executed.
568
569Example: set some flag and clear it again when the coroutine gets canceled
570or the function returns:
571
572 sub do_something {
573 my $guard = Coro::guard { $busy = 0 };
574 $busy = 1;
575
576 # do something that requires $busy to be true
577 }
578
579=cut
580
581sub guard(&) {
582 bless \(my $cb = $_[0]), "Coro::guard"
583}
584
585sub Coro::guard::cancel {
586 ${$_[0]} = sub { };
587}
588
589sub Coro::guard::DESTROY {
590 ${$_[0]}->();
591}
592
593
594=item unblock_sub { ... }
595
596This utility function takes a BLOCK or code reference and "unblocks" it,
597returning a new coderef. Unblocking means that calling the new coderef
598will return immediately without blocking, returning nothing, while the
599original code ref will be called (with parameters) from within another
600coroutine.
601
602The reason this function exists is that many event libraries (such as the
603venerable L<Event|Event> module) are not coroutine-safe (a weaker form
604of thread-safety). This means you must not block within event callbacks,
605otherwise you might suffer from crashes or worse. The only event library
606currently known that is safe to use without C<unblock_sub> is L<EV>.
607
608This function allows your callbacks to block by executing them in another
609coroutine where it is safe to block. One example where blocking is handy
610is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
611disk, for example.
612
613In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
614creating event callbacks that want to block.
615
616If your handler does not plan to block (e.g. simply sends a message to
617another coroutine, or puts some other coroutine into the ready queue),
618there is no reason to use C<unblock_sub>.
619
620Note that you also need to use C<unblock_sub> for any other callbacks that
621are indirectly executed by any C-based event loop. For example, when you
622use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
623provides callbacks that are the result of some event callback, then you
624must not block either, or use C<unblock_sub>.
625
626=cut
627
628our @unblock_queue;
629
630# we create a special coro because we want to cede,
631# to reduce pressure on the coro pool (because most callbacks
632# return immediately and can be reused) and because we cannot cede
633# inside an event callback.
634our $unblock_scheduler = new Coro sub {
635 while () {
636 while (my $cb = pop @unblock_queue) {
637 # this is an inlined copy of async_pool
638 my $coro = (pop @async_pool) || new Coro \&pool_handler;
639
640 $coro->{_invoke} = $cb;
641 $coro->ready;
642 cede; # for short-lived callbacks, this reduces pressure on the coro pool
70 } 643 }
71 } while (1); 644 schedule; # sleep well
72 }, $class; 645 }
73}
74
75=item $prev->transfer($next)
76
77Save the state of the current subroutine in $prev and switch to the
78coroutine saved in $next.
79
80=cut
81
82# I call the _transfer function from a perl function
83# because that way perl saves all important things on
84# the stack.
85sub transfer {
86 _transfer($_[0], $_[1]);
87}
88
89=item $error, $error_msg, $error_coro
90
91This coroutine will be called on fatal errors. C<$error_msg> and
92C<$error_coro> return the error message and the error-causing coroutine
93(NOT an object) respectively. This API might change.
94
95=cut
96
97$error_msg =
98$error_coro = undef;
99
100$error = _newprocess {
101 print STDERR "FATAL: $error_msg\nprogram aborted\n";
102 exit 50;
103}; 646};
647$unblock_scheduler->desc ("[unblock_sub scheduler]");
648
649sub unblock_sub(&) {
650 my $cb = shift;
651
652 sub {
653 unshift @unblock_queue, [$cb, @_];
654 $unblock_scheduler->ready;
655 }
656}
657
658=back
659
660=cut
104 661
1051; 6621;
106 663
107=back 664=head1 BUGS/LIMITATIONS
108 665
109=head1 BUGS 666This module is not perl-pseudo-thread-safe. You should only ever use this
110 667module from the same thread (this requirement might be removed in the
111This module has not yet been extensively tested. 668future to allow per-thread schedulers, but Coro::State does not yet allow
669this). I recommend disabling thread support and using processes, as this
670is much faster and uses less memory.
112 671
113=head1 SEE ALSO 672=head1 SEE ALSO
114 673
115L<Coro::Process>, L<Coro::Signal>. 674Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
675
676Debugging: L<Coro::Debug>.
677
678Support/Utility: L<Coro::Specific>, L<Coro::Util>.
679
680Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
681
682IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
683
684Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.
685
686XS API: L<Coro::MakeMaker>.
687
688Low level Configuration, Coroutine Environment: L<Coro::State>.
116 689
117=head1 AUTHOR 690=head1 AUTHOR
118 691
119 Marc Lehmann <pcg@goof.com> 692 Marc Lehmann <schmorp@schmorp.de>
120 http://www.goof.com/pcg/marc/ 693 http://home.schmorp.de/
121 694
122=cut 695=cut
123 696

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