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Revision 1.22 by root, Mon Jul 23 02:14:19 2001 UTC vs.
Revision 1.129 by root, Wed Sep 19 22:33:08 2007 UTC

8 8
9 async { 9 async {
10 # some asynchronous thread of execution 10 # some asynchronous thread of execution
11 }; 11 };
12 12
13 # alternatively create an async process like this: 13 # alternatively create an async coroutine like this:
14 14
15 sub some_func : Coro { 15 sub some_func : Coro {
16 # some more async code 16 # some more async code
17 } 17 }
18 18
19 cede; 19 cede;
20 20
21=head1 DESCRIPTION 21=head1 DESCRIPTION
22 22
23This module collection manages coroutines. Coroutines are similar to 23This module collection manages coroutines. Coroutines are similar
24Threads but don't run in parallel. 24to threads but don't run in parallel at the same time even on SMP
25machines. The specific flavor of coroutine used in this module also
26guarantees you that it will not switch between coroutines unless
27necessary, at easily-identified points in your program, so locking and
28parallel access are rarely an issue, making coroutine programming much
29safer than threads programming.
25 30
26This module is still experimental, see the BUGS section below. 31(Perl, however, does not natively support real threads but instead does a
32very slow and memory-intensive emulation of processes using threads. This
33is a performance win on Windows machines, and a loss everywhere else).
27 34
28In this module, coroutines are defined as "callchain + lexical variables 35In this module, coroutines are defined as "callchain + lexical variables +
29+ @_ + $_ + $@ + $^W), that is, a coroutine has it's own callchain, it's 36@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
30own set of lexicals and it's own set of perl's most important global 37its own set of lexicals and its own set of perls most important global
31variables. 38variables.
32 39
33WARNING: When using this module, make sure that, at program end, no
34coroutines are still running OR just call exit before falling off the
35end. The reason for this is that some coroutine of yours might have called
36into a C function, and falling off the end of main:: results in returning
37to that C function instead if to the main C interpreter.
38
39WARNING: Unless you really know what you are doing, do NOT do context
40switches inside callbacks from the XS level. The reason for this is
41similar to the reason above: A callback calls a perl function, this
42perl function does a context switch, some other callback is called, the
43original function returns from it - to what? To the wrong XS function,
44with totally different return values. Unfortunately, this includes
45callbacks done by perl itself (tie'd variables!).
46
47The only workaround for this is to do coroutines on C level.
48
49=cut 40=cut
50 41
51package Coro; 42package Coro;
52 43
44use strict;
45no warnings "uninitialized";
46
53use Coro::State; 47use Coro::State;
54 48
55use base Exporter; 49use base qw(Coro::State Exporter);
56 50
57$VERSION = 0.10; 51our $idle; # idle handler
52our $main; # main coroutine
53our $current; # current coroutine
58 54
55our $VERSION = '3.7';
56
59@EXPORT = qw(async cede schedule terminate current); 57our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
60@EXPORT_OK = qw($current); 58our %EXPORT_TAGS = (
59 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60);
61our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
61 62
62{ 63{
63 my @async; 64 my @async;
65 my $init;
64 66
65 # this way of handling attributes simply is NOT scalable ;() 67 # this way of handling attributes simply is NOT scalable ;()
66 sub import { 68 sub import {
69 no strict 'refs';
70
67 Coro->export_to_level(1, @_); 71 Coro->export_to_level (1, @_);
72
68 my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE}; 73 my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
69 *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub { 74 *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
70 my ($package, $ref) = (shift, shift); 75 my ($package, $ref) = (shift, shift);
71 my @attrs; 76 my @attrs;
72 for (@_) { 77 for (@_) {
73 if ($_ eq "Coro") { 78 if ($_ eq "Coro") {
74 push @async, $ref; 79 push @async, $ref;
80 unless ($init++) {
81 eval q{
82 sub INIT {
83 &async(pop @async) while @async;
84 }
85 };
86 }
75 } else { 87 } else {
76 push @attrs, $_; 88 push @attrs, $_;
77 } 89 }
78 } 90 }
79 return $old ? $old->($package, $ref, @attrs) : @attrs; 91 return $old ? $old->($package, $ref, @attrs) : @attrs;
80 }; 92 };
81 } 93 }
82 94
83 sub INIT {
84 &async(pop @async) while @async;
85 }
86} 95}
96
97=over 4
87 98
88=item $main 99=item $main
89 100
90This coroutine represents the main program. 101This coroutine represents the main program.
91 102
92=cut 103=cut
93 104
94our $main = new Coro; 105$main = new Coro;
95 106
96=item $current (or as function: current) 107=item $current (or as function: current)
97 108
98The current coroutine (the last coroutine switched to). The initial value is C<$main> (of course). 109The current coroutine (the last coroutine switched to). The initial value
110is C<$main> (of course).
111
112This variable is B<strictly> I<read-only>. It is provided for performance
113reasons. If performance is not essential you are encouraged to use the
114C<Coro::current> function instead.
99 115
100=cut 116=cut
101 117
102# maybe some other module used Coro::Specific before... 118# maybe some other module used Coro::Specific before...
103if ($current) {
104 $main->{specific} = $current->{specific}; 119$main->{specific} = $current->{specific}
105} 120 if $current;
106 121
107our $current = $main; 122_set_current $main;
108 123
109sub current() { $current } 124sub current() { $current }
110 125
111=item $idle 126=item $idle
112 127
113The coroutine to switch to when no other coroutine is running. The default 128A callback that is called whenever the scheduler finds no ready coroutines
114implementation prints "FATAL: deadlock detected" and exits. 129to run. The default implementation prints "FATAL: deadlock detected" and
130exits, because the program has no other way to continue.
115 131
116=cut 132This hook is overwritten by modules such as C<Coro::Timer> and
133C<Coro::Event> to wait on an external event that hopefully wake up a
134coroutine so the scheduler can run it.
117 135
118# should be done using priorities :( 136Please note that if your callback recursively invokes perl (e.g. for event
119our $idle = new Coro sub { 137handlers), then it must be prepared to be called recursively.
120 print STDERR "FATAL: deadlock detected\n"; 138
121 exit(51); 139=cut
140
141$idle = sub {
142 require Carp;
143 Carp::croak ("FATAL: deadlock detected");
122}; 144};
123 145
124# we really need priorities... 146sub _cancel {
125my @ready; # the ready queue. hehe, rather broken ;) 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.
160my @destroy;
161my $manager;
162
163$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);
126 175
127# static methods. not really. 176# static methods. not really.
128 177
178=back
179
129=head2 STATIC METHODS 180=head2 STATIC METHODS
130 181
131Static methods are actually functions that operate on the current process only. 182Static methods are actually functions that operate on the current coroutine only.
132 183
133=over 4 184=over 4
134 185
135=item async { ... } [@args...] 186=item async { ... } [@args...]
136 187
137Create a new asynchronous process and return it's process object 188Create a new asynchronous coroutine and return it's coroutine object
138(usually unused). When the sub returns the new process is automatically 189(usually unused). When the sub returns the new coroutine is automatically
139terminated. 190terminated.
191
192Calling C<exit> in a coroutine will do the same as calling exit outside
193the coroutine. Likewise, when the coroutine dies, the program will exit,
194just as it would in the main program.
140 195
141 # create a new coroutine that just prints its arguments 196 # create a new coroutine that just prints its arguments
142 async { 197 async {
143 print "@_\n"; 198 print "@_\n";
144 } 1,2,3,4; 199 } 1,2,3,4;
145 200
146The coderef you submit MUST NOT be a closure that refers to variables
147in an outer scope. This does NOT work. Pass arguments into it instead.
148
149=cut 201=cut
150 202
151sub async(&@) { 203sub async(&@) {
152 my $pid = new Coro @_; 204 my $coro = new Coro @_;
153 $pid->ready; 205 $coro->ready;
154 $pid; 206 $coro
207}
208
209=item async_pool { ... } [@args...]
210
211Similar to C<async>, but uses a coroutine pool, so you should not call
212terminate or join (although you are allowed to), and you get a coroutine
213that might have executed other code already (which can be good or bad :).
214
215Also, the block is executed in an C<eval> context and a warning will be
216issued in case of an exception instead of terminating the program, as
217C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
218will not work in the expected way, unless you call terminate or cancel,
219which somehow defeats the purpose of pooling.
220
221The priority will be reset to C<0> after each job, otherwise the coroutine
222will be re-used "as-is".
223
224The pool size is limited to 8 idle coroutines (this can be adjusted by
225changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
226required.
227
228If you are concerned about pooled coroutines growing a lot because a
229single C<async_pool> used a lot of stackspace you can e.g. C<async_pool {
230terminate }> once per second or so to slowly replenish the pool.
231
232=cut
233
234our $POOL_SIZE = 8;
235our @pool;
236
237sub 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
257sub 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
155} 265}
156 266
157=item schedule 267=item schedule
158 268
159Calls the scheduler. Please note that the current process will not be put 269Calls the scheduler. Please note that the current coroutine will not be put
160into the ready queue, so calling this function usually means you will 270into the ready queue, so calling this function usually means you will
161never be called again. 271never be called again unless something else (e.g. an event handler) calls
272ready.
162 273
163=cut 274The canonical way to wait on external events is this:
164 275
165my $prev; 276 {
277 # remember current coroutine
278 my $current = $Coro::current;
166 279
167sub schedule { 280 # register a hypothetical event handler
168 # should be done using priorities :( 281 on_event_invoke sub {
169 ($prev, $current) = ($current, shift @ready || $idle); 282 # wake up sleeping coroutine
170 Coro::State::transfer($prev, $current); 283 $current->ready;
171} 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 }
172 292
173=item cede 293=item cede
174 294
175"Cede" to other processes. This function puts the current process into the 295"Cede" to other coroutines. This function puts the current coroutine into the
176ready queue and calls C<schedule>, which has the effect of giving up the 296ready queue and calls C<schedule>, which has the effect of giving up the
177current "timeslice" to other coroutines of the same or higher priority. 297current "timeslice" to other coroutines of the same or higher priority.
178 298
179=cut 299Returns true if at least one coroutine switch has happened.
180 300
181sub cede { 301=item Coro::cede_notself
182 $current->ready;
183 &schedule;
184}
185 302
303Works like cede, but is not exported by default and will cede to any
304coroutine, regardless of priority, once.
305
306Returns true if at least one coroutine switch has happened.
307
186=item terminate 308=item terminate [arg...]
187 309
188Terminates the current process. 310Terminates the current coroutine with the given status values (see L<cancel>).
189
190Future versions of this function will allow result arguments.
191 311
192=cut 312=cut
193 313
194sub terminate { 314sub terminate {
195 my $self = $current; 315 $current->cancel (@_);
196 $self->{_results} = [@_];
197 $current = shift @ready || $idle;
198 Coro::State::transfer(delete $self->{_coro_state}, $current);
199 # cannot return
200 die;
201} 316}
202 317
203=back 318=back
204 319
205# dynamic methods 320# dynamic methods
206 321
207=head2 PROCESS METHODS 322=head2 COROUTINE METHODS
208 323
209These are the methods you can call on process objects. 324These are the methods you can call on coroutine objects.
210 325
211=over 4 326=over 4
212 327
213=item new Coro \&sub [, @args...] 328=item new Coro \&sub [, @args...]
214 329
215Create a new process and return it. When the sub returns the process 330Create a new coroutine and return it. When the sub returns the coroutine
216automatically terminates. To start the process you must first put it into 331automatically terminates as if C<terminate> with the returned values were
332called. To make the coroutine run you must first put it into the ready queue
217the ready queue by calling the ready method. 333by calling the ready method.
218 334
219The coderef you submit MUST NOT be a closure that refers to variables 335See C<async> for additional discussion.
220in an outer scope. This does NOT work. Pass arguments into it instead.
221 336
222=cut 337=cut
223 338
224sub _newcoro { 339sub _run_coro {
225 terminate &{+shift}; 340 terminate &{+shift};
226} 341}
227 342
228sub new { 343sub new {
229 my $class = shift; 344 my $class = shift;
230 bless {
231 _coro_state => (new Coro::State $_[0] && \&_newcoro, @_),
232 }, $class;
233}
234 345
235=item $process->ready 346 $class->SUPER::new (\&_run_coro, @_)
347}
236 348
237Put the current process into the ready queue. 349=item $success = $coroutine->ready
238 350
239=cut 351Put the given coroutine into the ready queue (according to it's priority)
352and return true. If the coroutine is already in the ready queue, do nothing
353and return false.
240 354
241sub ready { 355=item $is_ready = $coroutine->is_ready
242 push @ready, $_[0]; 356
357Return wether the coroutine is currently the ready queue or not,
358
359=item $coroutine->cancel (arg...)
360
361Terminates the given coroutine and makes it return the given arguments as
362status (default: the empty list). Never returns if the coroutine is the
363current coroutine.
364
365=cut
366
367sub 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
382Wait until the coroutine terminates and return any values given to the
383C<terminate> or C<cancel> functions. C<join> can be called multiple times
384from multiple coroutine.
385
386=cut
387
388sub 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 $coroutine->on_destroy (\&cb)
406
407Registers a callback that is called when this coroutine gets destroyed,
408but before it is joined. The callback gets passed the terminate arguments,
409if any.
410
411=cut
412
413sub on_destroy {
414 my ($self, $cb) = @_;
415
416 push @{ $self->{destroy_cb} }, $cb;
417}
418
419=item $oldprio = $coroutine->prio ($newprio)
420
421Sets (or gets, if the argument is missing) the priority of the
422coroutine. Higher priority coroutines get run before lower priority
423coroutines. Priorities are small signed integers (currently -4 .. +3),
424that you can refer to using PRIO_xxx constants (use the import tag :prio
425to 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
433The idle coroutine ($Coro::idle) always has a lower priority than any
434existing coroutine.
435
436Changing the priority of the current coroutine will take effect immediately,
437but changing the priority of coroutines in the ready queue (but not
438running) will only take effect after the next schedule (of that
439coroutine). This is a bug that will be fixed in some future version.
440
441=item $newprio = $coroutine->nice ($change)
442
443Similar to C<prio>, but subtract the given value from the priority (i.e.
444higher values mean lower priority, just as in unix).
445
446=item $olddesc = $coroutine->desc ($newdesc)
447
448Sets (or gets in case the argument is missing) the description for this
449coroutine. This is just a free-form string you can associate with a coroutine.
450
451=cut
452
453sub desc {
454 my $old = $_[0]{desc};
455 $_[0]{desc} = $_[1] if @_ > 1;
456 $old;
243} 457}
244 458
245=back 459=back
246 460
461=head2 GLOBAL FUNCTIONS
462
463=over 4
464
465=item Coro::nready
466
467Returns the number of coroutines that are currently in the ready state,
468i.e. that can be switched to. The value C<0> means that the only runnable
469coroutine is the currently running one, so C<cede> would have no effect,
470and C<schedule> would cause a deadlock unless there is an idle handler
471that wakes up some coroutines.
472
473=item my $guard = Coro::guard { ... }
474
475This creates and returns a guard object. Nothing happens until the object
476gets destroyed, in which case the codeblock given as argument will be
477executed. This is useful to free locks or other resources in case of a
478runtime error or when the coroutine gets canceled, as in both cases the
479guard block will be executed. The guard object supports only one method,
480C<< ->cancel >>, which will keep the codeblock from being executed.
481
482Example: set some flag and clear it again when the coroutine gets canceled
483or 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
494sub guard(&) {
495 bless \(my $cb = $_[0]), "Coro::guard"
496}
497
498sub Coro::guard::cancel {
499 ${$_[0]} = sub { };
500}
501
502sub Coro::guard::DESTROY {
503 ${$_[0]}->();
504}
505
506
507=item unblock_sub { ... }
508
509This utility function takes a BLOCK or code reference and "unblocks" it,
510returning the new coderef. This means that the new coderef will return
511immediately without blocking, returning nothing, while the original code
512ref will be called (with parameters) from within its own coroutine.
513
514The reason this function exists is that many event libraries (such as the
515venerable L<Event|Event> module) are not coroutine-safe (a weaker form
516of thread-safety). This means you must not block within event callbacks,
517otherwise you might suffer from crashes or worse.
518
519This function allows your callbacks to block by executing them in another
520coroutine where it is safe to block. One example where blocking is handy
521is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
522disk.
523
524In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
525creating event callbacks that want to block.
526
527=cut
528
529our @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.
535our $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
550sub unblock_sub(&) {
551 my $cb = shift;
552
553 sub {
554 unshift @unblock_queue, [$cb, @_];
555 $unblock_scheduler->ready;
556 }
557}
558
559=back
560
247=cut 561=cut
248 562
2491; 5631;
250 564
251=head1 BUGS/LIMITATIONS 565=head1 BUGS/LIMITATIONS
252 566
253 - could be faster, especially when the core would introduce special 567 - you must make very sure that no coro is still active on global
254 support for coroutines (like it does for threads). 568 destruction. very bad things might happen otherwise (usually segfaults).
255 - there is still a memleak on coroutine termination that I could not 569
256 identify. Could be as small as a single SV.
257 - this module is not well-tested.
258 - if variables or arguments "disappear" (become undef) or become
259 corrupted please contact the author so he cen iron out the
260 remaining bugs.
261 - this module is not thread-safe. You must only ever use this module from 570 - this module is not thread-safe. You should only ever use this module
262 the same thread (this requirement might be loosened in the future to 571 from the same thread (this requirement might be loosened in the future
263 allow per-thread schedulers, but Coro::State does not yet allow this). 572 to allow per-thread schedulers, but Coro::State does not yet allow
573 this).
264 574
265=head1 SEE ALSO 575=head1 SEE ALSO
266 576
267L<Coro::Channel>, L<Coro::Cont>, L<Coro::Specific>, L<Coro::Semaphore>, 577Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.
268L<Coro::Signal>, L<Coro::State>, L<Coro::Event>. 578
579Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
580
581Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.
582
583Embedding: L<Coro:MakeMaker>
269 584
270=head1 AUTHOR 585=head1 AUTHOR
271 586
272 Marc Lehmann <pcg@goof.com> 587 Marc Lehmann <schmorp@schmorp.de>
273 http://www.goof.com/pcg/marc/ 588 http://home.schmorp.de/
274 589
275=cut 590=cut
276 591

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