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Revision 1.266 by root, Wed Aug 26 07:41:07 2009 UTC

1=head1 NAME 1=head1 NAME
2 2
3Coro - coroutine process abstraction 3Coro - the only real threads in perl
4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use Coro; 7 use Coro;
8 8
9 async { 9 async {
10 # some asynchronous thread of execution 10 # some asynchronous thread of execution
11 print "2\n";
12 cede; # yield back to main
13 print "4\n";
11 }; 14 };
12 15 print "1\n";
13 # alternatively create an async coroutine like this: 16 cede; # yield to coro
14 17 print "3\n";
15 sub some_func : Coro { 18 cede; # and again
16 # some more async code 19
17 } 20 # use locking
18 21 use Coro::Semaphore;
19 cede; 22 my $lock = new Coro::Semaphore;
23 my $locked;
24
25 $lock->down;
26 $locked = 1;
27 $lock->up;
20 28
21=head1 DESCRIPTION 29=head1 DESCRIPTION
22 30
23This module collection manages coroutines. Coroutines are similar 31For a tutorial-style introduction, please read the L<Coro::Intro>
24to threads but don't run in parallel at the same time even on SMP 32manpage. This manpage mainly contains reference information.
25machines. The specific flavor of coroutine use din this module also
26guarentees 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.
30 33
31(Perl, however, does not natively support real threads but instead does a 34This module collection manages continuations in general, most often in
32very slow and memory-intensive emulation of processes using threads. This 35the form of cooperative threads (also called coros, or simply "coro"
33is a performance win on Windows machines, and a loss everywhere else). 36in the documentation). They are similar to kernel threads but don't (in
37general) run in parallel at the same time even on SMP machines. The
38specific flavor of thread offered by this module also guarantees you that
39it will not switch between threads unless necessary, at easily-identified
40points in your program, so locking and parallel access are rarely an
41issue, making thread programming much safer and easier than using other
42thread models.
34 43
44Unlike the so-called "Perl threads" (which are not actually real threads
45but only the windows process emulation (see section of same name for more
46details) ported to unix, and as such act as processes), Coro provides
47a full shared address space, which makes communication between threads
48very easy. And Coro's threads are fast, too: disabling the Windows
49process emulation code in your perl and using Coro can easily result in
50a two to four times speed increase for your programs. A parallel matrix
51multiplication benchmark runs over 300 times faster on a single core than
52perl's pseudo-threads on a quad core using all four cores.
53
54Coro achieves that by supporting multiple running interpreters that share
55data, which is especially useful to code pseudo-parallel processes and
56for event-based programming, such as multiple HTTP-GET requests running
57concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
58into an event-based environment.
59
35In this module, coroutines are defined as "callchain + lexical variables + 60In this module, a thread is defined as "callchain + lexical variables +
36@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain, 61some package variables + C stack), that is, a thread has its own callchain,
37its own set of lexicals and its own set of perls most important global 62its own set of lexicals and its own set of perls most important global
38variables. 63variables (see L<Coro::State> for more configuration and background info).
64
65See also the C<SEE ALSO> section at the end of this document - the Coro
66module family is quite large.
39 67
40=cut 68=cut
41 69
42package Coro; 70package Coro;
43 71
44use strict; 72use strict qw(vars subs);
45no warnings "uninitialized"; 73no warnings "uninitialized";
46 74
75use Guard ();
76
47use Coro::State; 77use Coro::State;
48 78
49use base qw(Coro::State Exporter); 79use base qw(Coro::State Exporter);
50 80
51our $idle; # idle handler 81our $idle; # idle handler
52our $main; # main coroutine 82our $main; # main coro
53our $current; # current coroutine 83our $current; # current coro
54 84
55our $VERSION = '3.3'; 85our $VERSION = 5.17;
56 86
57our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub); 87our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
58our %EXPORT_TAGS = ( 88our %EXPORT_TAGS = (
59 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)], 89 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60); 90);
61our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready)); 91our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
62 92
63{ 93=head1 GLOBAL VARIABLES
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 94
97=over 4 95=over 4
98 96
99=item $main 97=item $Coro::main
100 98
101This coroutine represents the main program. 99This variable stores the Coro object that represents the main
100program. While you cna C<ready> it and do most other things you can do to
101coro, it is mainly useful to compare again C<$Coro::current>, to see
102whether you are running in the main program or not.
102 103
103=cut 104=cut
104 105
105$main = new Coro; 106# $main is now being initialised by Coro::State
106 107
107=item $current (or as function: current) 108=item $Coro::current
108 109
109The current coroutine (the last coroutine switched to). The initial value 110The Coro object representing the current coro (the last
111coro that the Coro scheduler switched to). The initial value is
110is C<$main> (of course). 112C<$Coro::main> (of course).
111 113
112This variable is B<strictly> I<read-only>. It is provided for performance 114This variable is B<strictly> I<read-only>. You can take copies of the
113reasons. If performance is not essentiel you are encouraged to use the 115value stored in it and use it as any other Coro object, but you must
114C<Coro::current> function instead. 116not otherwise modify the variable itself.
115 117
116=cut 118=cut
117 119
118# maybe some other module used Coro::Specific before...
119$main->{specific} = $current->{specific}
120 if $current;
121
122_set_current $main;
123
124sub current() { $current } 120sub current() { $current } # [DEPRECATED]
125 121
126=item $idle 122=item $Coro::idle
127 123
124This variable is mainly useful to integrate Coro into event loops. It is
125usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
126pretty low-level functionality.
127
128This variable stores either a Coro object or a callback.
129
128A callback that is called whenever the scheduler finds no ready coroutines 130If it is a callback, the it is called whenever the scheduler finds no
129to run. The default implementation prints "FATAL: deadlock detected" and 131ready coros to run. The default implementation prints "FATAL:
130exits, because the program has no other way to continue. 132deadlock detected" and exits, because the program has no other way to
133continue.
131 134
135If it is a coro object, then this object will be readied (without
136invoking any ready hooks, however) when the scheduler finds no other ready
137coros to run.
138
132This hook is overwritten by modules such as C<Coro::Timer> and 139This hook is overwritten by modules such as C<Coro::EV> and
133C<Coro::Event> to wait on an external event that hopefully wake up a 140C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
134coroutine so the scheduler can run it. 141coro so the scheduler can run it.
142
143Note that the callback I<must not>, under any circumstances, block
144the current coro. Normally, this is achieved by having an "idle
145coro" that calls the event loop and then blocks again, and then
146readying that coro in the idle handler, or by simply placing the idle
147coro in this variable.
148
149See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
150technique.
135 151
136Please note that if your callback recursively invokes perl (e.g. for event 152Please note that if your callback recursively invokes perl (e.g. for event
137handlers), then it must be prepared to be called recursively. 153handlers), then it must be prepared to be called recursively itself.
138 154
139=cut 155=cut
140 156
141$idle = sub { 157$idle = sub {
142 require Carp; 158 require Carp;
143 Carp::croak ("FATAL: deadlock detected"); 159 Carp::croak ("FATAL: deadlock detected");
144}; 160};
145 161
146sub _cancel {
147 my ($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 162# this coro is necessary because a coro
159# cannot destroy itself. 163# cannot destroy itself.
160my @destroy; 164our @destroy;
161my $manager; 165our $manager;
162 166
163$manager = new Coro sub { 167$manager = new Coro sub {
164 while () { 168 while () {
165 (shift @destroy)->_cancel 169 Coro::State::cancel shift @destroy
166 while @destroy; 170 while @destroy;
167 171
168 &schedule; 172 &schedule;
169 } 173 }
170}; 174};
171 175$manager->{desc} = "[coro manager]";
172$manager->prio (PRIO_MAX); 176$manager->prio (PRIO_MAX);
173 177
174# static methods. not really.
175
176=back 178=back
177 179
178=head2 STATIC METHODS 180=head1 SIMPLE CORO CREATION
179
180Static methods are actually functions that operate on the current coroutine only.
181 181
182=over 4 182=over 4
183 183
184=item async { ... } [@args...] 184=item async { ... } [@args...]
185 185
186Create a new asynchronous coroutine and return it's coroutine object 186Create a new coro and return its Coro object (usually
187(usually unused). When the sub returns the new coroutine is automatically 187unused). The coro will be put into the ready queue, so
188it will start running automatically on the next scheduler run.
189
190The first argument is a codeblock/closure that should be executed in the
191coro. When it returns argument returns the coro is automatically
188terminated. 192terminated.
189 193
190Calling C<exit> in a coroutine will not work correctly, so do not do that. 194The remaining arguments are passed as arguments to the closure.
191 195
192When the coroutine dies, the program will exit, just as in the main 196See the C<Coro::State::new> constructor for info about the coro
193program. 197environment in which coro are executed.
194 198
199Calling C<exit> in a coro will do the same as calling exit outside
200the coro. Likewise, when the coro dies, the program will exit,
201just as it would in the main program.
202
203If you do not want that, you can provide a default C<die> handler, or
204simply avoid dieing (by use of C<eval>).
205
195 # create a new coroutine that just prints its arguments 206Example: Create a new coro that just prints its arguments.
207
196 async { 208 async {
197 print "@_\n"; 209 print "@_\n";
198 } 1,2,3,4; 210 } 1,2,3,4;
199 211
200=cut
201
202sub async(&@) {
203 my $coro = new Coro @_;
204 $coro->ready;
205 $coro
206}
207
208=item async_pool { ... } [@args...] 212=item async_pool { ... } [@args...]
209 213
210Similar to C<async>, but uses a coroutine pool, so you should not call 214Similar to C<async>, but uses a coro pool, so you should not call
211terminate or join (although you are allowed to), and you get a coroutine 215terminate or join on it (although you are allowed to), and you get a
212that might have executed other code already (which can be good or bad :). 216coro that might have executed other code already (which can be good
217or bad :).
213 218
219On the plus side, this function is about twice as fast as creating (and
220destroying) a completely new coro, so if you need a lot of generic
221coros in quick successsion, use C<async_pool>, not C<async>.
222
214Also, the block is executed in an C<eval> context and a warning will be 223The code block is executed in an C<eval> context and a warning will be
215issued in case of an exception instead of terminating the program, as 224issued in case of an exception instead of terminating the program, as
216C<async> does. As the coroutine is being reused, stuff like C<on_destroy> 225C<async> does. As the coro is being reused, stuff like C<on_destroy>
217will not work in the expected way, unless you call terminate or cancel, 226will not work in the expected way, unless you call terminate or cancel,
218which somehow defeats the purpose of pooling. 227which somehow defeats the purpose of pooling (but is fine in the
228exceptional case).
219 229
220The priority will be reset to C<0> after each job, otherwise the coroutine 230The priority will be reset to C<0> after each run, tracing will be
221will be re-used "as-is". 231disabled, the description will be reset and the default output filehandle
232gets restored, so you can change all these. Otherwise the coro will
233be re-used "as-is": most notably if you change other per-coro global
234stuff such as C<$/> you I<must needs> revert that change, which is most
235simply done by using local as in: C<< local $/ >>.
222 236
223The pool size is limited to 8 idle coroutines (this can be adjusted by 237The idle pool size is limited to C<8> idle coros (this can be
224changing $Coro::POOL_SIZE), and there can be as many non-idle coros as 238adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
225required. 239coros as required.
226 240
227If you are concerned about pooled coroutines growing a lot because a 241If you are concerned about pooled coros growing a lot because a
228single C<async_pool> used a lot of stackspace you can e.g. C<async_pool { 242single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
229terminate }> once per second or so to slowly replenish the pool. 243{ terminate }> once per second or so to slowly replenish the pool. In
244addition to that, when the stacks used by a handler grows larger than 32kb
245(adjustable via $Coro::POOL_RSS) it will also be destroyed.
230 246
231=cut 247=cut
232 248
233our $POOL_SIZE = 8; 249our $POOL_SIZE = 8;
250our $POOL_RSS = 32 * 1024;
234our @pool; 251our @async_pool;
235 252
236sub pool_handler { 253sub pool_handler {
237 while () { 254 while () {
238 my ($cb, @arg) = @{ delete $current->{_invoke} };
239
240 eval { 255 eval {
241 $cb->(@arg); 256 &{&_pool_handler} while 1;
242 }; 257 };
258
243 warn $@ if $@; 259 warn $@ if $@;
244
245 last if @pool >= $POOL_SIZE;
246 push @pool, $current;
247
248 $current->prio (0);
249 schedule;
250 } 260 }
251} 261}
252 262
253sub async_pool(&@) { 263=back
254 # this is also inlined into the unlock_scheduler
255 my $coro = (pop @pool or new Coro \&pool_handler);
256 264
257 $coro->{_invoke} = [@_]; 265=head1 STATIC METHODS
258 $coro->ready;
259 266
260 $coro 267Static methods are actually functions that implicitly operate on the
268current coro.
269
270=over 4
271
272=item schedule
273
274Calls the scheduler. The scheduler will find the next coro that is
275to be run from the ready queue and switches to it. The next coro
276to be run is simply the one with the highest priority that is longest
277in its ready queue. If there is no coro ready, it will clal the
278C<$Coro::idle> hook.
279
280Please note that the current coro will I<not> be put into the ready
281queue, so calling this function usually means you will never be called
282again unless something else (e.g. an event handler) calls C<< ->ready >>,
283thus waking you up.
284
285This makes C<schedule> I<the> generic method to use to block the current
286coro and wait for events: first you remember the current coro in
287a variable, then arrange for some callback of yours to call C<< ->ready
288>> on that once some event happens, and last you call C<schedule> to put
289yourself to sleep. Note that a lot of things can wake your coro up,
290so you need to check whether the event indeed happened, e.g. by storing the
291status in a variable.
292
293See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
294
295=item cede
296
297"Cede" to other coros. This function puts the current coro into
298the ready queue and calls C<schedule>, which has the effect of giving
299up the current "timeslice" to other coros of the same or higher
300priority. Once your coro gets its turn again it will automatically be
301resumed.
302
303This function is often called C<yield> in other languages.
304
305=item Coro::cede_notself
306
307Works like cede, but is not exported by default and will cede to I<any>
308coro, regardless of priority. This is useful sometimes to ensure
309progress is made.
310
311=item terminate [arg...]
312
313Terminates the current coro with the given status values (see L<cancel>).
314
315=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
316
317These function install enter and leave winders in the current scope. The
318enter block will be executed when on_enter is called and whenever the
319current coro is re-entered by the scheduler, while the leave block is
320executed whenever the current coro is blocked by the scheduler, and
321also when the containing scope is exited (by whatever means, be it exit,
322die, last etc.).
323
324I<Neither invoking the scheduler, nor exceptions, are allowed within those
325BLOCKs>. That means: do not even think about calling C<die> without an
326eval, and do not even think of entering the scheduler in any way.
327
328Since both BLOCKs are tied to the current scope, they will automatically
329be removed when the current scope exits.
330
331These functions implement the same concept as C<dynamic-wind> in scheme
332does, and are useful when you want to localise some resource to a specific
333coro.
334
335They slow down thread switching considerably for coros that use them
336(about 40% for a BLOCK with a single assignment, so thread switching is
337still reasonably fast if the handlers are fast).
338
339These functions are best understood by an example: The following function
340will change the current timezone to "Antarctica/South_Pole", which
341requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
342which remember/change the current timezone and restore the previous
343value, respectively, the timezone is only changed for the coro that
344installed those handlers.
345
346 use POSIX qw(tzset);
347
348 async {
349 my $old_tz; # store outside TZ value here
350
351 Coro::on_enter {
352 $old_tz = $ENV{TZ}; # remember the old value
353
354 $ENV{TZ} = "Antarctica/South_Pole";
355 tzset; # enable new value
356 };
357
358 Coro::on_leave {
359 $ENV{TZ} = $old_tz;
360 tzset; # restore old value
361 };
362
363 # at this place, the timezone is Antarctica/South_Pole,
364 # without disturbing the TZ of any other coro.
365 };
366
367This can be used to localise about any resource (locale, uid, current
368working directory etc.) to a block, despite the existance of other
369coros.
370
371Another interesting example implements time-sliced multitasking using
372interval timers (this could obviously be optimised, but does the job):
373
374 # "timeslice" the given block
375 sub timeslice(&) {
376 use Time::HiRes ();
377
378 Coro::on_enter {
379 # on entering the thread, we set an VTALRM handler to cede
380 $SIG{VTALRM} = sub { cede };
381 # and then start the interval timer
382 Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
383 };
384 Coro::on_leave {
385 # on leaving the thread, we stop the interval timer again
386 Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
387 };
388
389 &{+shift};
390 }
391
392 # use like this:
393 timeslice {
394 # The following is an endless loop that would normally
395 # monopolise the process. Since it runs in a timesliced
396 # environment, it will regularly cede to other threads.
397 while () { }
398 };
399
400
401=item killall
402
403Kills/terminates/cancels all coros except the currently running one.
404
405Note that while this will try to free some of the main interpreter
406resources if the calling coro isn't the main coro, but one
407cannot free all of them, so if a coro that is not the main coro
408calls this function, there will be some one-time resource leak.
409
410=cut
411
412sub killall {
413 for (Coro::State::list) {
414 $_->cancel
415 if $_ != $current && UNIVERSAL::isa $_, "Coro";
416 }
261} 417}
262 418
263=item schedule 419=back
264 420
265Calls the scheduler. Please note that the current coroutine will not be put 421=head1 CORO OBJECT METHODS
266into the ready queue, so calling this function usually means you will
267never be called again unless something else (e.g. an event handler) calls
268ready.
269 422
270The canonical way to wait on external events is this: 423These are the methods you can call on coro objects (or to create
424them).
271 425
426=over 4
427
428=item new Coro \&sub [, @args...]
429
430Create a new coro and return it. When the sub returns, the coro
431automatically terminates as if C<terminate> with the returned values were
432called. To make the coro run you must first put it into the ready
433queue by calling the ready method.
434
435See C<async> and C<Coro::State::new> for additional info about the
436coro environment.
437
438=cut
439
440sub _coro_run {
441 terminate &{+shift};
442}
443
444=item $success = $coro->ready
445
446Put the given coro into the end of its ready queue (there is one
447queue for each priority) and return true. If the coro is already in
448the ready queue, do nothing and return false.
449
450This ensures that the scheduler will resume this coro automatically
451once all the coro of higher priority and all coro of the same
452priority that were put into the ready queue earlier have been resumed.
453
454=item $coro->suspend
455
456Suspends the specified coro. A suspended coro works just like any other
457coro, except that the scheduler will not select a suspended coro for
458execution.
459
460Suspending a coro can be useful when you want to keep the coro from
461running, but you don't want to destroy it, or when you want to temporarily
462freeze a coro (e.g. for debugging) to resume it later.
463
464A scenario for the former would be to suspend all (other) coros after a
465fork and keep them alive, so their destructors aren't called, but new
466coros can be created.
467
468=item $coro->resume
469
470If the specified coro was suspended, it will be resumed. Note that when
471the coro was in the ready queue when it was suspended, it might have been
472unreadied by the scheduler, so an activation might have been lost.
473
474To avoid this, it is best to put a suspended coro into the ready queue
475unconditionally, as every synchronisation mechanism must protect itself
476against spurious wakeups, and the one in the Coro family certainly do
477that.
478
479=item $is_ready = $coro->is_ready
480
481Returns true iff the Coro object is in the ready queue. Unless the Coro
482object gets destroyed, it will eventually be scheduled by the scheduler.
483
484=item $is_running = $coro->is_running
485
486Returns true iff the Coro object is currently running. Only one Coro object
487can ever be in the running state (but it currently is possible to have
488multiple running Coro::States).
489
490=item $is_suspended = $coro->is_suspended
491
492Returns true iff this Coro object has been suspended. Suspended Coros will
493not ever be scheduled.
494
495=item $coro->cancel (arg...)
496
497Terminates the given Coro and makes it return the given arguments as
498status (default: the empty list). Never returns if the Coro is the
499current Coro.
500
501=cut
502
503sub cancel {
504 my $self = shift;
505
506 if ($current == $self) {
507 terminate @_;
508 } else {
509 $self->{_status} = [@_];
510 Coro::State::cancel $self;
272 { 511 }
273 # remember current coroutine 512}
513
514=item $coro->schedule_to
515
516Puts the current coro to sleep (like C<Coro::schedule>), but instead
517of continuing with the next coro from the ready queue, always switch to
518the given coro object (regardless of priority etc.). The readyness
519state of that coro isn't changed.
520
521This is an advanced method for special cases - I'd love to hear about any
522uses for this one.
523
524=item $coro->cede_to
525
526Like C<schedule_to>, but puts the current coro into the ready
527queue. This has the effect of temporarily switching to the given
528coro, and continuing some time later.
529
530This is an advanced method for special cases - I'd love to hear about any
531uses for this one.
532
533=item $coro->throw ([$scalar])
534
535If C<$throw> is specified and defined, it will be thrown as an exception
536inside the coro at the next convenient point in time. Otherwise
537clears the exception object.
538
539Coro will check for the exception each time a schedule-like-function
540returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
541>>, C<< Coro::Handle->readable >> and so on. Most of these functions
542detect this case and return early in case an exception is pending.
543
544The exception object will be thrown "as is" with the specified scalar in
545C<$@>, i.e. if it is a string, no line number or newline will be appended
546(unlike with C<die>).
547
548This can be used as a softer means than C<cancel> to ask a coro to
549end itself, although there is no guarantee that the exception will lead to
550termination, and if the exception isn't caught it might well end the whole
551program.
552
553You might also think of C<throw> as being the moral equivalent of
554C<kill>ing a coro with a signal (in this case, a scalar).
555
556=item $coro->join
557
558Wait until the coro terminates and return any values given to the
559C<terminate> or C<cancel> functions. C<join> can be called concurrently
560from multiple coro, and all will be resumed and given the status
561return once the C<$coro> terminates.
562
563=cut
564
565sub join {
566 my $self = shift;
567
568 unless ($self->{_status}) {
274 my $current = $Coro::current; 569 my $current = $current;
275 570
276 # register a hypothetical event handler 571 push @{$self->{_on_destroy}}, sub {
277 on_event_invoke sub {
278 # wake up sleeping coroutine
279 $current->ready; 572 $current->ready;
280 undef $current; 573 undef $current;
281 }; 574 };
282 575
283 # call schedule until event occured.
284 # in case we are woken up for other reasons
285 # (current still defined), loop.
286 Coro::schedule while $current;
287 }
288
289=item cede
290
291"Cede" to other coroutines. This function puts the current coroutine into the
292ready queue and calls C<schedule>, which has the effect of giving up the
293current "timeslice" to other coroutines of the same or higher priority.
294
295Returns true if at least one coroutine switch has happened.
296
297=item Coro::cede_notself
298
299Works like cede, but is not exported by default and will cede to any
300coroutine, regardless of priority, once.
301
302Returns true if at least one coroutine switch has happened.
303
304=item terminate [arg...]
305
306Terminates the current coroutine with the given status values (see L<cancel>).
307
308=cut
309
310sub terminate {
311 $current->cancel (@_);
312}
313
314=back
315
316# dynamic methods
317
318=head2 COROUTINE METHODS
319
320These are the methods you can call on coroutine objects.
321
322=over 4
323
324=item new Coro \&sub [, @args...]
325
326Create a new coroutine and return it. When the sub returns the coroutine
327automatically terminates as if C<terminate> with the returned values were
328called. To make the coroutine run you must first put it into the ready queue
329by calling the ready method.
330
331Calling C<exit> in a coroutine will not work correctly, so do not do that.
332
333=cut
334
335sub _run_coro {
336 terminate &{+shift};
337}
338
339sub new {
340 my $class = shift;
341
342 $class->SUPER::new (\&_run_coro, @_)
343}
344
345=item $success = $coroutine->ready
346
347Put the given coroutine into the ready queue (according to it's priority)
348and return true. If the coroutine is already in the ready queue, do nothing
349and return false.
350
351=item $is_ready = $coroutine->is_ready
352
353Return wether the coroutine is currently the ready queue or not,
354
355=item $coroutine->cancel (arg...)
356
357Terminates the given coroutine and makes it return the given arguments as
358status (default: the empty list). Never returns if the coroutine is the
359current coroutine.
360
361=cut
362
363sub cancel {
364 my $self = shift;
365 $self->{status} = [@_];
366
367 if ($current == $self) {
368 push @destroy, $self;
369 $manager->ready;
370 &schedule while 1;
371 } else {
372 $self->_cancel;
373 }
374}
375
376=item $coroutine->join
377
378Wait until the coroutine terminates and return any values given to the
379C<terminate> or C<cancel> functions. C<join> can be called multiple times
380from multiple coroutine.
381
382=cut
383
384sub join {
385 my $self = shift;
386
387 unless ($self->{status}) {
388 my $current = $current;
389
390 push @{$self->{destroy_cb}}, sub {
391 $current->ready;
392 undef $current;
393 };
394
395 &schedule while $current; 576 &schedule while $current;
396 } 577 }
397 578
398 wantarray ? @{$self->{status}} : $self->{status}[0]; 579 wantarray ? @{$self->{_status}} : $self->{_status}[0];
399} 580}
400 581
401=item $coroutine->on_destroy (\&cb) 582=item $coro->on_destroy (\&cb)
402 583
403Registers a callback that is called when this coroutine gets destroyed, 584Registers a callback that is called when this coro gets destroyed,
404but before it is joined. The callback gets passed the terminate arguments, 585but before it is joined. The callback gets passed the terminate arguments,
405if any. 586if any, and I<must not> die, under any circumstances.
406 587
407=cut 588=cut
408 589
409sub on_destroy { 590sub on_destroy {
410 my ($self, $cb) = @_; 591 my ($self, $cb) = @_;
411 592
412 push @{ $self->{destroy_cb} }, $cb; 593 push @{ $self->{_on_destroy} }, $cb;
413} 594}
414 595
415=item $oldprio = $coroutine->prio ($newprio) 596=item $oldprio = $coro->prio ($newprio)
416 597
417Sets (or gets, if the argument is missing) the priority of the 598Sets (or gets, if the argument is missing) the priority of the
418coroutine. Higher priority coroutines get run before lower priority 599coro. Higher priority coro get run before lower priority
419coroutines. Priorities are small signed integers (currently -4 .. +3), 600coro. Priorities are small signed integers (currently -4 .. +3),
420that you can refer to using PRIO_xxx constants (use the import tag :prio 601that you can refer to using PRIO_xxx constants (use the import tag :prio
421to get then): 602to get then):
422 603
423 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN 604 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
424 3 > 1 > 0 > -1 > -3 > -4 605 3 > 1 > 0 > -1 > -3 > -4
425 606
426 # set priority to HIGH 607 # set priority to HIGH
427 current->prio(PRIO_HIGH); 608 current->prio (PRIO_HIGH);
428 609
429The idle coroutine ($Coro::idle) always has a lower priority than any 610The idle coro ($Coro::idle) always has a lower priority than any
430existing coroutine. 611existing coro.
431 612
432Changing the priority of the current coroutine will take effect immediately, 613Changing the priority of the current coro will take effect immediately,
433but changing the priority of coroutines in the ready queue (but not 614but changing the priority of coro in the ready queue (but not
434running) will only take effect after the next schedule (of that 615running) will only take effect after the next schedule (of that
435coroutine). This is a bug that will be fixed in some future version. 616coro). This is a bug that will be fixed in some future version.
436 617
437=item $newprio = $coroutine->nice ($change) 618=item $newprio = $coro->nice ($change)
438 619
439Similar to C<prio>, but subtract the given value from the priority (i.e. 620Similar to C<prio>, but subtract the given value from the priority (i.e.
440higher values mean lower priority, just as in unix). 621higher values mean lower priority, just as in unix).
441 622
442=item $olddesc = $coroutine->desc ($newdesc) 623=item $olddesc = $coro->desc ($newdesc)
443 624
444Sets (or gets in case the argument is missing) the description for this 625Sets (or gets in case the argument is missing) the description for this
445coroutine. This is just a free-form string you can associate with a coroutine. 626coro. This is just a free-form string you can associate with a
627coro.
628
629This method simply sets the C<< $coro->{desc} >> member to the given
630string. You can modify this member directly if you wish.
446 631
447=cut 632=cut
448 633
449sub desc { 634sub desc {
450 my $old = $_[0]{desc}; 635 my $old = $_[0]{desc};
451 $_[0]{desc} = $_[1] if @_ > 1; 636 $_[0]{desc} = $_[1] if @_ > 1;
452 $old; 637 $old;
453} 638}
454 639
640sub transfer {
641 require Carp;
642 Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
643}
644
455=back 645=back
456 646
457=head2 GLOBAL FUNCTIONS 647=head1 GLOBAL FUNCTIONS
458 648
459=over 4 649=over 4
460 650
461=item Coro::nready 651=item Coro::nready
462 652
463Returns the number of coroutines that are currently in the ready state, 653Returns the number of coro that are currently in the ready state,
464i.e. that can be swicthed to. The value C<0> means that the only runnable 654i.e. that can be switched to by calling C<schedule> directory or
655indirectly. The value C<0> means that the only runnable coro is the
465coroutine is the currently running one, so C<cede> would have no effect, 656currently running one, so C<cede> would have no effect, and C<schedule>
466and C<schedule> would cause a deadlock unless there is an idle handler 657would cause a deadlock unless there is an idle handler that wakes up some
467that wakes up some coroutines. 658coro.
468 659
469=item my $guard = Coro::guard { ... } 660=item my $guard = Coro::guard { ... }
470 661
471This creates and returns a guard object. Nothing happens until the objetc 662This function still exists, but is deprecated. Please use the
472gets destroyed, in which case the codeblock given as argument will be 663C<Guard::guard> function instead.
473executed. This is useful to free locks or other resources in case of a
474runtime error or when the coroutine gets canceled, as in both cases the
475guard block will be executed. The guard object supports only one method,
476C<< ->cancel >>, which will keep the codeblock from being executed.
477 664
478Example: set some flag and clear it again when the coroutine gets canceled
479or the function returns:
480
481 sub do_something {
482 my $guard = Coro::guard { $busy = 0 };
483 $busy = 1;
484
485 # do something that requires $busy to be true
486 }
487
488=cut 665=cut
489 666
490sub guard(&) { 667BEGIN { *guard = \&Guard::guard }
491 bless \(my $cb = $_[0]), "Coro::guard"
492}
493
494sub Coro::guard::cancel {
495 ${$_[0]} = sub { };
496}
497
498sub Coro::guard::DESTROY {
499 ${$_[0]}->();
500}
501
502 668
503=item unblock_sub { ... } 669=item unblock_sub { ... }
504 670
505This utility function takes a BLOCK or code reference and "unblocks" it, 671This utility function takes a BLOCK or code reference and "unblocks" it,
506returning the new coderef. This means that the new coderef will return 672returning a new coderef. Unblocking means that calling the new coderef
507immediately without blocking, returning nothing, while the original code 673will return immediately without blocking, returning nothing, while the
508ref will be called (with parameters) from within its own coroutine. 674original code ref will be called (with parameters) from within another
675coro.
509 676
510The reason this fucntion exists is that many event libraries (such as the 677The reason this function exists is that many event libraries (such as the
511venerable L<Event|Event> module) are not coroutine-safe (a weaker form 678venerable L<Event|Event> module) are not thread-safe (a weaker form
512of thread-safety). This means you must not block within event callbacks, 679of reentrancy). This means you must not block within event callbacks,
513otherwise you might suffer from crashes or worse. 680otherwise you might suffer from crashes or worse. The only event library
681currently known that is safe to use without C<unblock_sub> is L<EV>.
514 682
515This function allows your callbacks to block by executing them in another 683This function allows your callbacks to block by executing them in another
516coroutine where it is safe to block. One example where blocking is handy 684coro where it is safe to block. One example where blocking is handy
517is when you use the L<Coro::AIO|Coro::AIO> functions to save results to 685is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
518disk. 686disk, for example.
519 687
520In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when 688In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
521creating event callbacks that want to block. 689creating event callbacks that want to block.
690
691If your handler does not plan to block (e.g. simply sends a message to
692another coro, or puts some other coro into the ready queue), there is
693no reason to use C<unblock_sub>.
694
695Note that you also need to use C<unblock_sub> for any other callbacks that
696are indirectly executed by any C-based event loop. For example, when you
697use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
698provides callbacks that are the result of some event callback, then you
699must not block either, or use C<unblock_sub>.
522 700
523=cut 701=cut
524 702
525our @unblock_queue; 703our @unblock_queue;
526 704
527# we create a special coro because we want to cede, 705# we create a special coro because we want to cede,
528# to reduce pressure on the coro pool (because most callbacks 706# to reduce pressure on the coro pool (because most callbacks
529# return immediately and can be reused) and because we cannot cede 707# return immediately and can be reused) and because we cannot cede
530# inside an event callback. 708# inside an event callback.
531our $unblock_scheduler = async { 709our $unblock_scheduler = new Coro sub {
532 while () { 710 while () {
533 while (my $cb = pop @unblock_queue) { 711 while (my $cb = pop @unblock_queue) {
534 # this is an inlined copy of async_pool 712 &async_pool (@$cb);
535 my $coro = (pop @pool or new Coro \&pool_handler);
536 713
537 $coro->{_invoke} = $cb;
538 $coro->ready;
539 cede; # for short-lived callbacks, this reduces pressure on the coro pool 714 # for short-lived callbacks, this reduces pressure on the coro pool
715 # as the chance is very high that the async_poll coro will be back
716 # in the idle state when cede returns
717 cede;
540 } 718 }
541 schedule; # sleep well 719 schedule; # sleep well
542 } 720 }
543}; 721};
722$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
544 723
545sub unblock_sub(&) { 724sub unblock_sub(&) {
546 my $cb = shift; 725 my $cb = shift;
547 726
548 sub { 727 sub {
549 unshift @unblock_queue, [$cb, @_]; 728 unshift @unblock_queue, [$cb, @_];
550 $unblock_scheduler->ready; 729 $unblock_scheduler->ready;
551 } 730 }
552} 731}
553 732
733=item $cb = Coro::rouse_cb
734
735Create and return a "rouse callback". That's a code reference that,
736when called, will remember a copy of its arguments and notify the owner
737coro of the callback.
738
739See the next function.
740
741=item @args = Coro::rouse_wait [$cb]
742
743Wait for the specified rouse callback (or the last one that was created in
744this coro).
745
746As soon as the callback is invoked (or when the callback was invoked
747before C<rouse_wait>), it will return the arguments originally passed to
748the rouse callback. In scalar context, that means you get the I<last>
749argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
750statement at the end.
751
752See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
753
554=back 754=back
555 755
556=cut 756=cut
557 757
5581; 7581;
559 759
760=head1 HOW TO WAIT FOR A CALLBACK
761
762It is very common for a coro to wait for some callback to be
763called. This occurs naturally when you use coro in an otherwise
764event-based program, or when you use event-based libraries.
765
766These typically register a callback for some event, and call that callback
767when the event occured. In a coro, however, you typically want to
768just wait for the event, simplyifying things.
769
770For example C<< AnyEvent->child >> registers a callback to be called when
771a specific child has exited:
772
773 my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
774
775But from within a coro, you often just want to write this:
776
777 my $status = wait_for_child $pid;
778
779Coro offers two functions specifically designed to make this easy,
780C<Coro::rouse_cb> and C<Coro::rouse_wait>.
781
782The first function, C<rouse_cb>, generates and returns a callback that,
783when invoked, will save its arguments and notify the coro that
784created the callback.
785
786The second function, C<rouse_wait>, waits for the callback to be called
787(by calling C<schedule> to go to sleep) and returns the arguments
788originally passed to the callback.
789
790Using these functions, it becomes easy to write the C<wait_for_child>
791function mentioned above:
792
793 sub wait_for_child($) {
794 my ($pid) = @_;
795
796 my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
797
798 my ($rpid, $rstatus) = Coro::rouse_wait;
799 $rstatus
800 }
801
802In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
803you can roll your own, using C<schedule>:
804
805 sub wait_for_child($) {
806 my ($pid) = @_;
807
808 # store the current coro in $current,
809 # and provide result variables for the closure passed to ->child
810 my $current = $Coro::current;
811 my ($done, $rstatus);
812
813 # pass a closure to ->child
814 my $watcher = AnyEvent->child (pid => $pid, cb => sub {
815 $rstatus = $_[1]; # remember rstatus
816 $done = 1; # mark $rstatus as valud
817 });
818
819 # wait until the closure has been called
820 schedule while !$done;
821
822 $rstatus
823 }
824
825
560=head1 BUGS/LIMITATIONS 826=head1 BUGS/LIMITATIONS
561 827
562 - you must make very sure that no coro is still active on global 828=over 4
563 destruction. very bad things might happen otherwise (usually segfaults).
564 829
830=item fork with pthread backend
831
832When Coro is compiled using the pthread backend (which isn't recommended
833but required on many BSDs as their libcs are completely broken), then
834coro will not survive a fork. There is no known workaround except to
835fix your libc and use a saner backend.
836
837=item perl process emulation ("threads")
838
565 - this module is not thread-safe. You should only ever use this module 839This module is not perl-pseudo-thread-safe. You should only ever use this
566 from the same thread (this requirement might be losened in the future 840module from the first thread (this requirement might be removed in the
567 to allow per-thread schedulers, but Coro::State does not yet allow 841future to allow per-thread schedulers, but Coro::State does not yet allow
568 this). 842this). I recommend disabling thread support and using processes, as having
843the windows process emulation enabled under unix roughly halves perl
844performance, even when not used.
845
846=item coro switching is not signal safe
847
848You must not switch to another coro from within a signal handler
849(only relevant with %SIG - most event libraries provide safe signals).
850
851That means you I<MUST NOT> call any function that might "block" the
852current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
853anything that calls those. Everything else, including calling C<ready>,
854works.
855
856=back
857
858
859=head1 WINDOWS PROCESS EMULATION
860
861A great many people seem to be confused about ithreads (for example, Chip
862Salzenberg called me unintelligent, incapable, stupid and ingullible,
863while in the same mail making rather confused statements about perl
864ithreads (for example, that memory or files would be shared), showing his
865lack of understanding of this area - if it is hard to understand for Chip,
866it is probably not obvious to everybody).
867
868What follows is an ultra-condensed version of my talk about threads in
869scripting languages given onthe perl workshop 2009:
870
871The so-called "ithreads" were originally implemented for two reasons:
872first, to (badly) emulate unix processes on native win32 perls, and
873secondly, to replace the older, real thread model ("5.005-threads").
874
875It does that by using threads instead of OS processes. The difference
876between processes and threads is that threads share memory (and other
877state, such as files) between threads within a single process, while
878processes do not share anything (at least not semantically). That
879means that modifications done by one thread are seen by others, while
880modifications by one process are not seen by other processes.
881
882The "ithreads" work exactly like that: when creating a new ithreads
883process, all state is copied (memory is copied physically, files and code
884is copied logically). Afterwards, it isolates all modifications. On UNIX,
885the same behaviour can be achieved by using operating system processes,
886except that UNIX typically uses hardware built into the system to do this
887efficiently, while the windows process emulation emulates this hardware in
888software (rather efficiently, but of course it is still much slower than
889dedicated hardware).
890
891As mentioned before, loading code, modifying code, modifying data
892structures and so on is only visible in the ithreads process doing the
893modification, not in other ithread processes within the same OS process.
894
895This is why "ithreads" do not implement threads for perl at all, only
896processes. What makes it so bad is that on non-windows platforms, you can
897actually take advantage of custom hardware for this purpose (as evidenced
898by the forks module, which gives you the (i-) threads API, just much
899faster).
900
901Sharing data is in the i-threads model is done by transfering data
902structures between threads using copying semantics, which is very slow -
903shared data simply does not exist. Benchmarks using i-threads which are
904communication-intensive show extremely bad behaviour with i-threads (in
905fact, so bad that Coro, which cannot take direct advantage of multiple
906CPUs, is often orders of magnitude faster because it shares data using
907real threads, refer to my talk for details).
908
909As summary, i-threads *use* threads to implement processes, while
910the compatible forks module *uses* processes to emulate, uhm,
911processes. I-threads slow down every perl program when enabled, and
912outside of windows, serve no (or little) practical purpose, but
913disadvantages every single-threaded Perl program.
914
915This is the reason that I try to avoid the name "ithreads", as it is
916misleading as it implies that it implements some kind of thread model for
917perl, and prefer the name "windows process emulation", which describes the
918actual use and behaviour of it much better.
569 919
570=head1 SEE ALSO 920=head1 SEE ALSO
571 921
922Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
923
924Debugging: L<Coro::Debug>.
925
572Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>. 926Support/Utility: L<Coro::Specific>, L<Coro::Util>.
573 927
574Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>. 928Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
929L<Coro::SemaphoreSet>, L<Coro::RWLock>.
575 930
576Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>. 931I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
577 932
578Embedding: L<Coro:MakeMaker> 933Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
934a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
935L<Coro::Select>.
936
937XS API: L<Coro::MakeMaker>.
938
939Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
579 940
580=head1 AUTHOR 941=head1 AUTHOR
581 942
582 Marc Lehmann <schmorp@schmorp.de> 943 Marc Lehmann <schmorp@schmorp.de>
583 http://home.schmorp.de/ 944 http://home.schmorp.de/

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