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Revision 1.181 by root, Fri May 9 22:04:37 2008 UTC

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 my $lock = new Coro::Semaphore;
22 print "back in main\n"; 22 my $locked;
23
24 $lock->down;
25 $locked = 1;
26 $lock->up;
23 27
24=head1 DESCRIPTION 28=head1 DESCRIPTION
25 29
26This module implements coroutines. Coroutines, similar to continuations, 30This module collection manages coroutines. Coroutines are similar to
27allow you to run more than one "thread of execution" in parallel. Unlike 31threads but don't (in general) run in parallel at the same time even
28threads this, only voluntary switching is used so locking problems are 32on SMP machines. The specific flavor of coroutine used in this module
29greatly reduced. 33also guarantees you that it will not switch between coroutines unless
34necessary, at easily-identified points in your program, so locking and
35parallel access are rarely an issue, making coroutine programming much
36safer and easier than threads programming.
30 37
31Although this is the "main" module of the Coro family it provides only 38Unlike a normal perl program, however, coroutines allow you to have
32low-level functionality. See L<Coro::Process> and related modules for a 39multiple running interpreters that share data, which is especially useful
33more useful process abstraction including scheduling. 40to code pseudo-parallel processes, such as multiple HTTP-GET requests
41running concurrently.
42
43Coroutines are also useful because Perl has no support for threads (the so
44called "threads" that perl offers are nothing more than the (bad) process
45emulation coming from the Windows platform: On standard operating systems
46they serve no purpose whatsoever, except by making your programs slow and
47making them use a lot of memory. Best disable them when building perl, or
48aks your software vendor/distributor to do it for you).
49
50In this module, coroutines are defined as "callchain + lexical variables +
51@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
52its own set of lexicals and its own set of perls most important global
53variables (see L<Coro::State> for more configuration).
54
55=cut
56
57package Coro;
58
59use strict;
60no warnings "uninitialized";
61
62use Coro::State;
63
64use base qw(Coro::State Exporter);
65
66our $idle; # idle handler
67our $main; # main coroutine
68our $current; # current coroutine
69
70our $VERSION = 4.6;
71
72our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
73our %EXPORT_TAGS = (
74 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
75);
76our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
34 77
35=over 4 78=over 4
36 79
37=cut 80=item $Coro::main
38 81
39package Coro; 82This variable stores the coroutine object that represents the main
83program. While you cna C<ready> it and do most other things you can do to
84coroutines, it is mainly useful to compare again C<$Coro::current>, to see
85wether you are running in the main program or not.
40 86
41BEGIN { 87=cut
42 $VERSION = 0.03;
43 88
89$main = new Coro;
90
91=item $Coro::current
92
93The coroutine object representing the current coroutine (the last
94coroutine that the Coro scheduler switched to). The initial value is
95C<$main> (of course).
96
97This variable is B<strictly> I<read-only>. You can take copies of the
98value stored in it and use it as any other coroutine object, but you must
99not otherwise modify the variable itself.
100
101=cut
102
103$main->{desc} = "[main::]";
104
105# maybe some other module used Coro::Specific before...
106$main->{_specific} = $current->{_specific}
107 if $current;
108
109_set_current $main;
110
111sub current() { $current } # [DEPRECATED]
112
113=item $Coro::idle
114
115This variable is mainly useful to integrate Coro into event loops. It is
116usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is
117pretty low-level functionality.
118
119This variable stores a callback that is called whenever the scheduler
120finds no ready coroutines to run. The default implementation prints
121"FATAL: deadlock detected" and exits, because the program has no other way
122to continue.
123
124This hook is overwritten by modules such as C<Coro::Timer> and
125C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
126coroutine so the scheduler can run it.
127
128Note that the callback I<must not>, under any circumstances, block
129the current coroutine. Normally, this is achieved by having an "idle
130coroutine" that calls the event loop and then blocks again, and then
131readying that coroutine in the idle handler.
132
133See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
134technique.
135
136Please note that if your callback recursively invokes perl (e.g. for event
137handlers), then it must be prepared to be called recursively itself.
138
139=cut
140
141$idle = sub {
44 require XSLoader; 142 require Carp;
45 XSLoader::load Coro, $VERSION; 143 Carp::croak ("FATAL: deadlock detected");
46} 144};
47 145
48=item $coro = new [$coderef [, @args]] 146sub _cancel {
147 my ($self) = @_;
49 148
50Create a new coroutine and return it. The first C<transfer> call to this 149 # free coroutine data and mark as destructed
51coroutine will start execution at the given coderef. If, the subroutine 150 $self->_destroy
52returns it will be executed again. 151 or return;
53 152
54If the coderef is omitted this function will create a new "empty" 153 # call all destruction callbacks
55coroutine, i.e. a coroutine that cannot be transfered to but can be used 154 $_->(@{$self->{_status}})
56to save the current coroutine in. 155 for @{(delete $self->{_on_destroy}) || []};
156}
57 157
158# this coroutine is necessary because a coroutine
159# cannot destroy itself.
160my @destroy;
161my $manager;
162
163$manager = new Coro sub {
164 while () {
165 (shift @destroy)->_cancel
166 while @destroy;
167
168 &schedule;
169 }
170};
171$manager->desc ("[coro manager]");
172$manager->prio (PRIO_MAX);
173
174=back
175
176=head2 SIMPLE COROUTINE CREATION
177
178=over 4
179
180=item async { ... } [@args...]
181
182Create a new coroutine and return it's coroutine object (usually
183unused). The coroutine will be put into the ready queue, so
184it will start running automatically on the next scheduler run.
185
186The first argument is a codeblock/closure that should be executed in the
187coroutine. When it returns argument returns the coroutine is automatically
188terminated.
189
190The remaining arguments are passed as arguments to the closure.
191
192See the C<Coro::State::new> constructor for info about the coroutine
193environment in which coroutines are executed.
194
195Calling C<exit> in a coroutine will do the same as calling exit outside
196the coroutine. Likewise, when the coroutine dies, the program will exit,
197just as it would in the main program.
198
199If you do not want that, you can provide a default C<die> handler, or
200simply avoid dieing (by use of C<eval>).
201
202Example: Create a new coroutine that just prints its arguments.
203
204 async {
205 print "@_\n";
206 } 1,2,3,4;
207
58=cut 208=cut
209
210sub async(&@) {
211 my $coro = new Coro @_;
212 $coro->ready;
213 $coro
214}
215
216=item async_pool { ... } [@args...]
217
218Similar to C<async>, but uses a coroutine pool, so you should not call
219terminate or join on it (although you are allowed to), and you get a
220coroutine that might have executed other code already (which can be good
221or bad :).
222
223On the plus side, this function is faster than creating (and destroying)
224a completely new coroutine, so if you need a lot of generic coroutines in
225quick successsion, use C<async_pool>, not C<async>.
226
227The code block is executed in an C<eval> context and a warning will be
228issued in case of an exception instead of terminating the program, as
229C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
230will not work in the expected way, unless you call terminate or cancel,
231which somehow defeats the purpose of pooling (but is fine in the
232exceptional case).
233
234The priority will be reset to C<0> after each run, tracing will be
235disabled, the description will be reset and the default output filehandle
236gets restored, so you can change all these. Otherwise the coroutine will
237be re-used "as-is": most notably if you change other per-coroutine global
238stuff such as C<$/> you I<must needs> to revert that change, which is most
239simply done by using local as in: C< local $/ >.
240
241The pool size is limited to C<8> idle coroutines (this can be adjusted by
242changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
243required.
244
245If you are concerned about pooled coroutines growing a lot because a
246single 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
248addition to that, when the stacks used by a handler grows larger than 16kb
249(adjustable via $Coro::POOL_RSS) it will also be destroyed.
250
251=cut
252
253our $POOL_SIZE = 8;
254our $POOL_RSS = 16 * 1024;
255our @async_pool;
256
257sub pool_handler {
258 my $cb;
259
260 while () {
261 eval {
262 while () {
263 _pool_1 $cb;
264 &$cb;
265 _pool_2 $cb;
266 &schedule;
267 }
268 };
269
270 last if $@ eq "\3async_pool terminate\2\n";
271 warn $@ if $@;
272 }
273}
274
275sub async_pool(&@) {
276 # this is also inlined into the unlock_scheduler
277 my $coro = (pop @async_pool) || new Coro \&pool_handler;
278
279 $coro->{_invoke} = [@_];
280 $coro->ready;
281
282 $coro
283}
284
285=back
286
287=head2 STATIC METHODS
288
289Static methods are actually functions that operate on the current coroutine.
290
291=over 4
292
293=item schedule
294
295Calls the scheduler. The scheduler will find the next coroutine that is
296to be run from the ready queue and switches to it. The next coroutine
297to be run is simply the one with the highest priority that is longest
298in its ready queue. If there is no coroutine ready, it will clal the
299C<$Coro::idle> hook.
300
301Please note that the current coroutine will I<not> be put into the ready
302queue, so calling this function usually means you will never be called
303again unless something else (e.g. an event handler) calls C<< ->ready >>,
304thus waking you up.
305
306This makes C<schedule> I<the> generic method to use to block the current
307coroutine and wait for events: first you remember the current coroutine in
308a variable, then arrange for some callback of yours to call C<< ->ready
309>> on that once some event happens, and last you call C<schedule> to put
310yourself to sleep. Note that a lot of things can wake your coroutine up,
311so you need to check wether the event indeed happened, e.g. by storing the
312status in a variable.
313
314The canonical way to wait on external events is this:
315
316 {
317 # remember current coroutine
318 my $current = $Coro::current;
319
320 # register a hypothetical event handler
321 on_event_invoke sub {
322 # wake up sleeping coroutine
323 $current->ready;
324 undef $current;
325 };
326
327 # call schedule until event occurred.
328 # in case we are woken up for other reasons
329 # (current still defined), loop.
330 Coro::schedule while $current;
331 }
332
333=item cede
334
335"Cede" to other coroutines. This function puts the current coroutine into
336the ready queue and calls C<schedule>, which has the effect of giving
337up the current "timeslice" to other coroutines of the same or higher
338priority. Once your coroutine gets its turn again it will automatically be
339resumed.
340
341This function is often called C<yield> in other languages.
342
343=item Coro::cede_notself
344
345Works like cede, but is not exported by default and will cede to I<any>
346coroutine, regardless of priority. This is useful sometimes to ensure
347progress is made.
348
349=item terminate [arg...]
350
351Terminates the current coroutine with the given status values (see L<cancel>).
352
353=item killall
354
355Kills/terminates/cancels all coroutines except the currently running
356one. This is useful after a fork, either in the child or the parent, as
357usually only one of them should inherit the running coroutines.
358
359Note that while this will try to free some of the main programs resources,
360you cnanot free all of them, so if a coroutine that is not the main
361program calls this function, there will be some one-time resource leak.
362
363=cut
364
365sub terminate {
366 $current->cancel (@_);
367}
368
369sub killall {
370 for (Coro::State::list) {
371 $_->cancel
372 if $_ != $current && UNIVERSAL::isa $_, "Coro";
373 }
374}
375
376=back
377
378=head2 COROUTINE METHODS
379
380These are the methods you can call on coroutine objects (or to create
381them).
382
383=over 4
384
385=item new Coro \&sub [, @args...]
386
387Create a new coroutine and return it. When the sub returns, the coroutine
388automatically terminates as if C<terminate> with the returned values were
389called. To make the coroutine run you must first put it into the ready
390queue by calling the ready method.
391
392See C<async> and C<Coro::State::new> for additional info about the
393coroutine environment.
394
395=cut
396
397sub _run_coro {
398 terminate &{+shift};
399}
59 400
60sub new { 401sub new {
61 my $class = $_[0]; 402 my $class = shift;
62 my $proc = $_[1] || sub { die "tried to transfer to an empty coroutine" };
63 bless _newprocess {
64 do {
65 eval { &$proc };
66 if ($@) {
67 $error_msg = $@;
68 $error_coro = _newprocess { };
69 &transfer($error_coro, $error);
70 }
71 } while (1);
72 }, $class;
73}
74 403
75=item $prev->transfer($next) 404 $class->SUPER::new (\&_run_coro, @_)
405}
76 406
77Save the state of the current subroutine in C<$prev> and switch to the 407=item $success = $coroutine->ready
78coroutine saved in C<$next>.
79 408
80The "state" of a subroutine only ever includes scope, i.e. lexical 409Put the given coroutine into the end of its ready queue (there is one
81variables and the current execution state. It does not save/restore any 410queue for each priority) and return true. If the coroutine is already in
82global variables such as C<$_> or C<$@> or any other special or non 411the ready queue, do nothing and return false.
83special variables. So remember that every function call that might call
84C<transfer> (such as C<Coro::Channel::put>) might clobber any global
85and/or special variables. Yes, this is by design ;) You cna always create
86your own process abstraction model that saves these variables.
87 412
88The easiest way to do this is to create your own scheduling primitive like this: 413This ensures that the scheduler will resume this coroutine automatically
414once all the coroutines of higher priority and all coroutines of the same
415priority that were put into the ready queue earlier have been resumed.
89 416
90 sub schedule { 417=item $is_ready = $coroutine->is_ready
91 local ($_, $@, ...); 418
92 $old->transfer($new); 419Return wether the coroutine is currently the ready queue or not,
420
421=item $coroutine->cancel (arg...)
422
423Terminates the given coroutine and makes it return the given arguments as
424status (default: the empty list). Never returns if the coroutine is the
425current coroutine.
426
427=cut
428
429sub cancel {
430 my $self = shift;
431 $self->{_status} = [@_];
432
433 if ($current == $self) {
434 push @destroy, $self;
435 $manager->ready;
436 &schedule while 1;
437 } else {
438 $self->_cancel;
93 } 439 }
94
95=cut
96
97# I call the _transfer function from a perl function
98# because that way perl saves all important things on
99# the stack. Actually, I'd do it from within XS, but
100# I couldn't get it to work.
101sub transfer {
102 _transfer($_[0], $_[1]);
103} 440}
104 441
105=item $error, $error_msg, $error_coro 442=item $coroutine->join
106 443
107This coroutine will be called on fatal errors. C<$error_msg> and 444Wait until the coroutine terminates and return any values given to the
108C<$error_coro> return the error message and the error-causing coroutine 445C<terminate> or C<cancel> functions. C<join> can be called concurrently
109(NOT an object) respectively. This API might change. 446from multiple coroutines, and all will be resumed and given the status
447return once the C<$coroutine> terminates.
110 448
111=cut 449=cut
112 450
113$error_msg = 451sub join {
114$error_coro = undef; 452 my $self = shift;
115 453
116$error = _newprocess { 454 unless ($self->{_status}) {
117 print STDERR "FATAL: $error_msg\nprogram aborted\n"; 455 my $current = $current;
118 exit 50; 456
457 push @{$self->{_on_destroy}}, sub {
458 $current->ready;
459 undef $current;
460 };
461
462 &schedule while $current;
463 }
464
465 wantarray ? @{$self->{_status}} : $self->{_status}[0];
466}
467
468=item $coroutine->on_destroy (\&cb)
469
470Registers a callback that is called when this coroutine gets destroyed,
471but before it is joined. The callback gets passed the terminate arguments,
472if any, and I<must not> die, under any circumstances.
473
474=cut
475
476sub on_destroy {
477 my ($self, $cb) = @_;
478
479 push @{ $self->{_on_destroy} }, $cb;
480}
481
482=item $oldprio = $coroutine->prio ($newprio)
483
484Sets (or gets, if the argument is missing) the priority of the
485coroutine. Higher priority coroutines get run before lower priority
486coroutines. Priorities are small signed integers (currently -4 .. +3),
487that you can refer to using PRIO_xxx constants (use the import tag :prio
488to get then):
489
490 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
491 3 > 1 > 0 > -1 > -3 > -4
492
493 # set priority to HIGH
494 current->prio(PRIO_HIGH);
495
496The idle coroutine ($Coro::idle) always has a lower priority than any
497existing coroutine.
498
499Changing the priority of the current coroutine will take effect immediately,
500but changing the priority of coroutines in the ready queue (but not
501running) will only take effect after the next schedule (of that
502coroutine). This is a bug that will be fixed in some future version.
503
504=item $newprio = $coroutine->nice ($change)
505
506Similar to C<prio>, but subtract the given value from the priority (i.e.
507higher values mean lower priority, just as in unix).
508
509=item $olddesc = $coroutine->desc ($newdesc)
510
511Sets (or gets in case the argument is missing) the description for this
512coroutine. This is just a free-form string you can associate with a coroutine.
513
514This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
515can modify this member directly if you wish.
516
517=item $coroutine->throw ([$scalar])
518
519If C<$throw> is specified and defined, it will be thrown as an exception
520inside the coroutine at the next convinient point in time (usually after
521it gains control at the next schedule/transfer/cede). Otherwise clears the
522exception object.
523
524The exception object will be thrown "as is" with the specified scalar in
525C<$@>, i.e. if it is a string, no line number or newline will be appended
526(unlike with C<die>).
527
528This can be used as a softer means than C<cancel> to ask a coroutine to
529end itself, although there is no guarentee that the exception will lead to
530termination, and if the exception isn't caught it might well end the whole
531program.
532
533=cut
534
535sub desc {
536 my $old = $_[0]{desc};
537 $_[0]{desc} = $_[1] if @_ > 1;
538 $old;
539}
540
541=back
542
543=head2 GLOBAL FUNCTIONS
544
545=over 4
546
547=item Coro::nready
548
549Returns the number of coroutines that are currently in the ready state,
550i.e. that can be switched to by calling C<schedule> directory or
551indirectly. The value C<0> means that the only runnable coroutine is the
552currently running one, so C<cede> would have no effect, and C<schedule>
553would cause a deadlock unless there is an idle handler that wakes up some
554coroutines.
555
556=item my $guard = Coro::guard { ... }
557
558This creates and returns a guard object. Nothing happens until the object
559gets destroyed, in which case the codeblock given as argument will be
560executed. This is useful to free locks or other resources in case of a
561runtime error or when the coroutine gets canceled, as in both cases the
562guard block will be executed. The guard object supports only one method,
563C<< ->cancel >>, which will keep the codeblock from being executed.
564
565Example: set some flag and clear it again when the coroutine gets canceled
566or the function returns:
567
568 sub do_something {
569 my $guard = Coro::guard { $busy = 0 };
570 $busy = 1;
571
572 # do something that requires $busy to be true
573 }
574
575=cut
576
577sub guard(&) {
578 bless \(my $cb = $_[0]), "Coro::guard"
579}
580
581sub Coro::guard::cancel {
582 ${$_[0]} = sub { };
583}
584
585sub Coro::guard::DESTROY {
586 ${$_[0]}->();
587}
588
589
590=item unblock_sub { ... }
591
592This utility function takes a BLOCK or code reference and "unblocks" it,
593returning a new coderef. Unblocking means that calling the new coderef
594will return immediately without blocking, returning nothing, while the
595original code ref will be called (with parameters) from within another
596coroutine.
597
598The reason this function exists is that many event libraries (such as the
599venerable L<Event|Event> module) are not coroutine-safe (a weaker form
600of thread-safety). This means you must not block within event callbacks,
601otherwise you might suffer from crashes or worse. The only event library
602currently known that is safe to use without C<unblock_sub> is L<EV>.
603
604This function allows your callbacks to block by executing them in another
605coroutine where it is safe to block. One example where blocking is handy
606is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
607disk, for example.
608
609In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
610creating event callbacks that want to block.
611
612If your handler does not plan to block (e.g. simply sends a message to
613another coroutine, or puts some other coroutine into the ready queue),
614there is no reason to use C<unblock_sub>.
615
616=cut
617
618our @unblock_queue;
619
620# we create a special coro because we want to cede,
621# to reduce pressure on the coro pool (because most callbacks
622# return immediately and can be reused) and because we cannot cede
623# inside an event callback.
624our $unblock_scheduler = new Coro sub {
625 while () {
626 while (my $cb = pop @unblock_queue) {
627 # this is an inlined copy of async_pool
628 my $coro = (pop @async_pool) || new Coro \&pool_handler;
629
630 $coro->{_invoke} = $cb;
631 $coro->ready;
632 cede; # for short-lived callbacks, this reduces pressure on the coro pool
633 }
634 schedule; # sleep well
635 }
119}; 636};
637$unblock_scheduler->desc ("[unblock_sub scheduler]");
638
639sub unblock_sub(&) {
640 my $cb = shift;
641
642 sub {
643 unshift @unblock_queue, [$cb, @_];
644 $unblock_scheduler->ready;
645 }
646}
647
648=back
649
650=cut
120 651
1211; 6521;
122 653
123=back 654=head1 BUGS/LIMITATIONS
124 655
125=head1 BUGS 656This module is not perl-pseudo-thread-safe. You should only ever use this
126 657module from the same thread (this requirement might be removed in the
127This module has not yet been extensively tested. 658future to allow per-thread schedulers, but Coro::State does not yet allow
659this). I recommend disabling thread support and using processes, as this
660is much faster and uses less memory.
128 661
129=head1 SEE ALSO 662=head1 SEE ALSO
130 663
131L<Coro::Process>, L<Coro::Signal>. 664Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
665
666Debugging: L<Coro::Debug>.
667
668Support/Utility: L<Coro::Specific>, L<Coro::Util>.
669
670Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
671
672IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
673
674Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.
675
676XS API: L<Coro::MakeMaker>.
677
678Low level Configuration, Coroutine Environment: L<Coro::State>.
132 679
133=head1 AUTHOR 680=head1 AUTHOR
134 681
135 Marc Lehmann <pcg@goof.com> 682 Marc Lehmann <schmorp@schmorp.de>
136 http://www.goof.com/pcg/marc/ 683 http://home.schmorp.de/
137 684
138=cut 685=cut
139 686

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