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40points in your program, so locking and parallel access are rarely an 40points in your program, so locking and parallel access are rarely an
41issue, making thread programming much safer and easier than using other 41issue, making thread programming much safer and easier than using other
42thread models. 42thread models.
43 43
44Unlike the so-called "Perl threads" (which are not actually real threads 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 45but only the windows process emulation (see section of same name for
46details) ported to unix, and as such act as processes), Coro provides 46more details) ported to UNIX, and as such act as processes), Coro
47a full shared address space, which makes communication between threads 47provides a full shared address space, which makes communication between
48very easy. And Coro's threads are fast, too: disabling the Windows 48threads very easy. And coro threads are fast, too: disabling the Windows
49process emulation code in your perl and using Coro can easily result in 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 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 51multiplication benchmark (very communication-intensive) runs over 300
52perl's pseudo-threads on a quad core using all four cores. 52times faster on a single core than perls pseudo-threads on a quad core
53using all four cores.
53 54
54Coro achieves that by supporting multiple running interpreters that share 55Coro achieves that by supporting multiple running interpreters that share
55data, which is especially useful to code pseudo-parallel processes and 56data, which is especially useful to code pseudo-parallel processes and
56for event-based programming, such as multiple HTTP-GET requests running 57for event-based programming, such as multiple HTTP-GET requests running
57concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro 58concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
63variables (see L<Coro::State> for more configuration and background info). 64variables (see L<Coro::State> for more configuration and background info).
64 65
65See also the C<SEE ALSO> section at the end of this document - the Coro 66See also the C<SEE ALSO> section at the end of this document - the Coro
66module family is quite large. 67module family is quite large.
67 68
69=head1 CORO THREAD LIFE CYCLE
70
71During the long and exciting (or not) life of a coro thread, it goes
72through a number of states:
73
74=over 4
75
76=item 1. Creation
77
78The first thing in the life of a coro thread is it's creation -
79obviously. The typical way to create a thread is to call the C<async
80BLOCK> function:
81
82 async {
83 # thread code goes here
84 };
85
86You can also pass arguments, which are put in C<@_>:
87
88 async {
89 print $_[1]; # prints 2
90 } 1, 2, 3;
91
92This creates a new coro thread and puts it into the ready queue, meaning
93it will run as soon as the CPU is free for it.
94
95C<async> will return a coro object - you can store this for future
96reference or ignore it, the thread itself will keep a reference to it's
97thread object - threads are alive on their own.
98
99Another way to create a thread is to call the C<new> constructor with a
100code-reference:
101
102 new Coro sub {
103 # thread code goes here
104 }, @optional_arguments;
105
106This is quite similar to calling C<async>, but the important difference is
107that the new thread is not put into the ready queue, so the thread will
108not run until somebody puts it there. C<async> is, therefore, identical to
109this sequence:
110
111 my $coro = new Coro sub {
112 # thread code goes here
113 };
114 $coro->ready;
115 return $coro;
116
117=item 2. Startup
118
119When a new coro thread is created, only a copy of the code reference
120and the arguments are stored, no extra memory for stacks and so on is
121allocated, keeping the coro thread in a low-memory state.
122
123Only when it actually starts executing will all the resources be finally
124allocated.
125
126The optional arguments specified at coro creation are available in C<@_>,
127similar to function calls.
128
129=item 3. Running / Blocking
130
131A lot can happen after the coro thread has started running. Quite usually,
132it will not run to the end in one go (because you could use a function
133instead), but it will give up the CPU regularly because it waits for
134external events.
135
136As long as a coro thread runs, it's coro object is available in the global
137variable C<$Coro::current>.
138
139The low-level way to give up the CPU is to call the scheduler, which
140selects a new coro thread to run:
141
142 Coro::schedule;
143
144Since running threads are not in the ready queue, calling the scheduler
145without doing anything else will block the coro thread forever - you need
146to arrange either for the coro to put woken up (readied) by some other
147event or some other thread, or you can put it into the ready queue before
148scheduling:
149
150 # this is exactly what Coro::cede does
151 $Coro::current->ready;
152 Coro::schedule;
153
154All the higher-level synchronisation methods (Coro::Semaphore,
155Coro::rouse_*...) are actually implemented via C<< ->ready >> and C<<
156Coro::schedule >>.
157
158While the coro thread is running it also might get assigned a C-level
159thread, or the C-level thread might be unassigned from it, as the Coro
160runtime wishes. A C-level thread needs to be assigned when your perl
161thread calls into some C-level function and that function in turn calls
162perl and perl then wants to switch coroutines. This happens most often
163when you run an event loop and block in the callback, or when perl
164itself calls some function such as C<AUTOLOAD> or methods via the C<tie>
165mechanism.
166
167=item 4. Termination
168
169Many threads actually terminate after some time. There are a number of
170ways to terminate a coro thread, the simplest is returning from the
171top-level code reference:
172
173 async {
174 # after returning from here, the coro thread is terminated
175 };
176
177 async {
178 return if 0.5 < rand; # terminate a little earlier, maybe
179 print "got a chance to print this\n";
180 # or here
181 };
182
183Any values returned from the coroutine can be recovered using C<< ->join
184>>:
185
186 my $coro = async {
187 "hello, world\n" # return a string
188 };
189
190 my $hello_world = $coro->join;
191
192 print $hello_world;
193
194Another way to terminate is to call C<< Coro::terminate >>, which at any
195subroutine call nesting level:
196
197 async {
198 Coro::terminate "return value 1", "return value 2";
199 };
200
201And yet another way is to C<< ->cancel >> (or C<< ->safe_cancel >>) the
202coro thread from another thread:
203
204 my $coro = async {
205 exit 1;
206 };
207
208 $coro->cancel; # also accepts values for ->join to retrieve
209
210Cancellation I<can> be dangerous - it's a bit like calling C<exit> without
211actually exiting, and might leave C libraries and XS modules in a weird
212state. Unlike other thread implementations, however, Coro is exceptionally
213safe with regards to cancellation, as perl will always be in a consistent
214state, and for those cases where you want to do truly marvellous things
215with your coro while it is being cancelled - that is, make sure all
216cleanup code is executed from the thread being cancelled - there is even a
217C<< ->safe_cancel >> method.
218
219So, cancelling a thread that runs in an XS event loop might not be the
220best idea, but any other combination that deals with perl only (cancelling
221when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is
222safe.
223
224=item 5. Cleanup
225
226Threads will allocate various resources. Most but not all will be returned
227when a thread terminates, during clean-up.
228
229Cleanup is quite similar to throwing an uncaught exception: perl will
230work it's way up through all subroutine calls and blocks. On it's way, it
231will release all C<my> variables, undo all C<local>'s and free any other
232resources truly local to the thread.
233
234So, a common way to free resources is to keep them referenced only by my
235variables:
236
237 async {
238 my $big_cache = new Cache ...;
239 };
240
241If there are no other references, then the C<$big_cache> object will be
242freed when the thread terminates, regardless of how it does so.
243
244What it does C<NOT> do is unlock any Coro::Semaphores or similar
245resources, but that's where the C<guard> methods come in handy:
246
247 my $sem = new Coro::Semaphore;
248
249 async {
250 my $lock_guard = $sem->guard;
251 # if we reutrn, or die or get cancelled, here,
252 # then the semaphore will be "up"ed.
253 };
254
255The C<Guard::guard> function comes in handy for any custom cleanup you
256might want to do:
257
258 async {
259 my $window = new Gtk2::Window "toplevel";
260 # The window will not be cleaned up automatically, even when $window
261 # gets freed, so use a guard to ensure it's destruction
262 # in case of an error:
263 my $window_guard = Guard::guard { $window->destroy };
264
265 # we are safe here
266 };
267
268Last not least, C<local> can often be handy, too, e.g. when temporarily
269replacing the coro thread description:
270
271 sub myfunction {
272 local $Coro::current->{desc} = "inside myfunction(@_)";
273
274 # if we return or die here, the description will be restored
275 }
276
277=item 6. Viva La Zombie Muerte
278
279Even after a thread has terminated and cleaned up it's resources, the coro
280object still is there and stores the return values of the thread. Only in
281this state will the coro object be "reference counted" in the normal perl
282sense: the thread code keeps a reference to it when it is active, but not
283after it has terminated.
284
285The means the coro object gets freed automatically when the thread has
286terminated and cleaned up and there arenot other references.
287
288If there are, the coro object will stay around, and you can call C<<
289->join >> as many times as you wish to retrieve the result values:
290
291 async {
292 print "hi\n";
293 1
294 };
295
296 # run the async above, and free everything before returning
297 # from Coro::cede:
298 Coro::cede;
299
300 {
301 my $coro = async {
302 print "hi\n";
303 1
304 };
305
306 # run the async above, and clean up, but do not free the coro
307 # object:
308 Coro::cede;
309
310 # optionally retrieve the result values
311 my @results = $coro->join;
312
313 # now $coro goes out of scope, and presumably gets freed
314 };
315
316=back
317
68=cut 318=cut
69 319
70package Coro; 320package Coro;
71 321
72use common::sense; 322use common::sense;
81 331
82our $idle; # idle handler 332our $idle; # idle handler
83our $main; # main coro 333our $main; # main coro
84our $current; # current coro 334our $current; # current coro
85 335
86our $VERSION = 5.25; 336our $VERSION = 5.372;
87 337
88our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait); 338our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait);
89our %EXPORT_TAGS = ( 339our %EXPORT_TAGS = (
90 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)], 340 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
91); 341);
131 381
132The default implementation dies with "FATAL: deadlock detected.", followed 382The default implementation dies with "FATAL: deadlock detected.", followed
133by a thread listing, because the program has no other way to continue. 383by a thread listing, because the program has no other way to continue.
134 384
135This hook is overwritten by modules such as C<Coro::EV> and 385This hook is overwritten by modules such as C<Coro::EV> and
136C<Coro::AnyEvent> to wait on an external event that hopefully wake up a 386C<Coro::AnyEvent> to wait on an external event that hopefully wakes up a
137coro so the scheduler can run it. 387coro so the scheduler can run it.
138 388
139See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique. 389See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
140 390
141=cut 391=cut
152our @destroy; 402our @destroy;
153our $manager; 403our $manager;
154 404
155$manager = new Coro sub { 405$manager = new Coro sub {
156 while () { 406 while () {
157 Coro::State::cancel shift @destroy 407 _destroy shift @destroy
158 while @destroy; 408 while @destroy;
159 409
160 &schedule; 410 &schedule;
161 } 411 }
162}; 412};
296coro, regardless of priority. This is useful sometimes to ensure 546coro, regardless of priority. This is useful sometimes to ensure
297progress is made. 547progress is made.
298 548
299=item terminate [arg...] 549=item terminate [arg...]
300 550
301Terminates the current coro with the given status values (see L<cancel>). 551Terminates the current coro with the given status values (see
552L<cancel>). The values will not be copied, but referenced directly.
302 553
303=item Coro::on_enter BLOCK, Coro::on_leave BLOCK 554=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
304 555
305These function install enter and leave winders in the current scope. The 556These function install enter and leave winders in the current scope. The
306enter block will be executed when on_enter is called and whenever the 557enter block will be executed when on_enter is called and whenever the
480Returns true iff this Coro object has been suspended. Suspended Coros will 731Returns true iff this Coro object has been suspended. Suspended Coros will
481not ever be scheduled. 732not ever be scheduled.
482 733
483=item $coro->cancel (arg...) 734=item $coro->cancel (arg...)
484 735
485Terminates the given Coro and makes it return the given arguments as 736Terminates the given Coro thread and makes it return the given arguments as
486status (default: the empty list). Never returns if the Coro is the 737status (default: an empty list). Never returns if the Coro is the
487current Coro. 738current Coro.
488 739
489=cut 740This is a rather brutal way to free a coro, with some limitations - if
741the thread is inside a C callback that doesn't expect to be canceled,
742bad things can happen, or if the cancelled thread insists on running
743complicated cleanup handlers that rely on it'S thread context, things will
744not work.
490 745
491sub cancel { 746Any cleanup code being run (e.g. from C<guard> blocks) will be run without
492 my $self = shift; 747a thread context, and is not allowed to switch to other threads. On the
748plus side, C<< ->cancel >> will always clean up the thread, no matter
749what. If your cleanup code is complex or you want to avoid cancelling a
750C-thread that doesn't know how to clean up itself, it can be better to C<<
751->throw >> an exception, or use C<< ->safe_cancel >>.
493 752
494 if ($current == $self) { 753The arguments to C<< ->cancel >> are not copied, but instead will
495 terminate @_; 754be referenced directly (e.g. if you pass C<$var> and after the call
496 } else { 755change that variable, then you might change the return values passed to
497 $self->{_status} = [@_]; 756e.g. C<join>, so don't do that).
498 Coro::State::cancel $self; 757
758The resources of the Coro are usually freed (or destructed) before this
759call returns, but this can be delayed for an indefinite amount of time, as
760in some cases the manager thread has to run first to actually destruct the
761Coro object.
762
763=item $coro->safe_cancel ($arg...)
764
765Works mostly like C<< ->cancel >>, but is inherently "safer", and
766consequently, can fail with an exception in cases the thread is not in a
767cancellable state.
768
769This method works a bit like throwing an exception that cannot be caught
770- specifically, it will clean up the thread from within itself, so
771all cleanup handlers (e.g. C<guard> blocks) are run with full thread
772context and can block if they wish. The downside is that there is no
773guarantee that the thread can be cancelled when you call this method, and
774therefore, it might fail. It is also considerably slower than C<cancel> or
775C<terminate>.
776
777A thread is in a safe-cancellable state if it either hasn't been run yet,
778or it has no C context attached and is inside an SLF function.
779
780The latter two basically mean that the thread isn't currently inside a
781perl callback called from some C function (usually via some XS modules)
782and isn't currently executing inside some C function itself (via Coro's XS
783API).
784
785This call returns true when it could cancel the thread, or croaks with an
786error otherwise (i.e. it either returns true or doesn't return at all).
787
788Why the weird interface? Well, there are two common models on how and
789when to cancel things. In the first, you have the expectation that your
790coro thread can be cancelled when you want to cancel it - if the thread
791isn't cancellable, this would be a bug somewhere, so C<< ->safe_cancel >>
792croaks to notify of the bug.
793
794In the second model you sometimes want to ask nicely to cancel a thread,
795but if it's not a good time, well, then don't cancel. This can be done
796relatively easy like this:
797
798 if (! eval { $coro->safe_cancel }) {
799 warn "unable to cancel thread: $@";
499 } 800 }
500} 801
802However, what you never should do is first try to cancel "safely" and
803if that fails, cancel the "hard" way with C<< ->cancel >>. That makes
804no sense: either you rely on being able to execute cleanup code in your
805thread context, or you don't. If you do, then C<< ->safe_cancel >> is the
806only way, and if you don't, then C<< ->cancel >> is always faster and more
807direct.
501 808
502=item $coro->schedule_to 809=item $coro->schedule_to
503 810
504Puts the current coro to sleep (like C<Coro::schedule>), but instead 811Puts the current coro to sleep (like C<Coro::schedule>), but instead
505of continuing with the next coro from the ready queue, always switch to 812of continuing with the next coro from the ready queue, always switch to
524inside the coro at the next convenient point in time. Otherwise 831inside the coro at the next convenient point in time. Otherwise
525clears the exception object. 832clears the exception object.
526 833
527Coro will check for the exception each time a schedule-like-function 834Coro will check for the exception each time a schedule-like-function
528returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down 835returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
529>>, C<< Coro::Handle->readable >> and so on. Most of these functions 836>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
530detect this case and return early in case an exception is pending. 837that are part of Coro itself) detect this case and return early in case an
838exception is pending.
531 839
532The exception object will be thrown "as is" with the specified scalar in 840The exception object will be thrown "as is" with the specified scalar in
533C<$@>, i.e. if it is a string, no line number or newline will be appended 841C<$@>, i.e. if it is a string, no line number or newline will be appended
534(unlike with C<die>). 842(unlike with C<die>).
535 843
536This can be used as a softer means than C<cancel> to ask a coro to 844This can be used as a softer means than either C<cancel> or C<safe_cancel
537end itself, although there is no guarantee that the exception will lead to 845>to ask a coro to end itself, although there is no guarantee that the
538termination, and if the exception isn't caught it might well end the whole 846exception will lead to termination, and if the exception isn't caught it
539program. 847might well end the whole program.
540 848
541You might also think of C<throw> as being the moral equivalent of 849You might also think of C<throw> as being the moral equivalent of
542C<kill>ing a coro with a signal (in this case, a scalar). 850C<kill>ing a coro with a signal (in this case, a scalar).
543 851
544=item $coro->join 852=item $coro->join
545 853
546Wait until the coro terminates and return any values given to the 854Wait until the coro terminates and return any values given to the
547C<terminate> or C<cancel> functions. C<join> can be called concurrently 855C<terminate> or C<cancel> functions. C<join> can be called concurrently
548from multiple coro, and all will be resumed and given the status 856from multiple threads, and all will be resumed and given the status
549return once the C<$coro> terminates. 857return once the C<$coro> terminates.
550 858
551=cut 859=cut
552 860
553sub join { 861sub join {
562 }; 870 };
563 871
564 &schedule while $current; 872 &schedule while $current;
565 } 873 }
566 874
567 wantarray ? @{$self->{_status}} : $self->{_status}[0]; 875 wantarray ? @{$self->{_status}} : $self->{_status}[0]
568} 876}
569 877
570=item $coro->on_destroy (\&cb) 878=item $coro->on_destroy (\&cb)
571 879
572Registers a callback that is called when this coro gets destroyed, 880Registers a callback that is called when this coro thread gets destroyed,
573but before it is joined. The callback gets passed the terminate arguments, 881that is, after it's resources have been freed but before it is joined. The
882callback gets passed the terminate/cancel arguments, if any, and I<must
574if any, and I<must not> die, under any circumstances. 883not> die, under any circumstances.
884
885There can be any number of C<on_destroy> callbacks per coro, and there is
886no way currently to remove a callback once added.
575 887
576=cut 888=cut
577 889
578sub on_destroy { 890sub on_destroy {
579 my ($self, $cb) = @_; 891 my ($self, $cb) = @_;
582} 894}
583 895
584=item $oldprio = $coro->prio ($newprio) 896=item $oldprio = $coro->prio ($newprio)
585 897
586Sets (or gets, if the argument is missing) the priority of the 898Sets (or gets, if the argument is missing) the priority of the
587coro. Higher priority coro get run before lower priority 899coro thread. Higher priority coro get run before lower priority
588coro. Priorities are small signed integers (currently -4 .. +3), 900coros. Priorities are small signed integers (currently -4 .. +3),
589that you can refer to using PRIO_xxx constants (use the import tag :prio 901that you can refer to using PRIO_xxx constants (use the import tag :prio
590to get then): 902to get then):
591 903
592 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN 904 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
593 3 > 1 > 0 > -1 > -3 > -4 905 3 > 1 > 0 > -1 > -3 > -4
594 906
595 # set priority to HIGH 907 # set priority to HIGH
596 current->prio (PRIO_HIGH); 908 current->prio (PRIO_HIGH);
597 909
598The idle coro ($Coro::idle) always has a lower priority than any 910The idle coro thread ($Coro::idle) always has a lower priority than any
599existing coro. 911existing coro.
600 912
601Changing the priority of the current coro will take effect immediately, 913Changing the priority of the current coro will take effect immediately,
602but changing the priority of coro in the ready queue (but not 914but changing the priority of a coro in the ready queue (but not running)
603running) will only take effect after the next schedule (of that 915will only take effect after the next schedule (of that coro). This is a
604coro). This is a bug that will be fixed in some future version. 916bug that will be fixed in some future version.
605 917
606=item $newprio = $coro->nice ($change) 918=item $newprio = $coro->nice ($change)
607 919
608Similar to C<prio>, but subtract the given value from the priority (i.e. 920Similar to C<prio>, but subtract the given value from the priority (i.e.
609higher values mean lower priority, just as in unix). 921higher values mean lower priority, just as in UNIX's nice command).
610 922
611=item $olddesc = $coro->desc ($newdesc) 923=item $olddesc = $coro->desc ($newdesc)
612 924
613Sets (or gets in case the argument is missing) the description for this 925Sets (or gets in case the argument is missing) the description for this
614coro. This is just a free-form string you can associate with a 926coro thread. This is just a free-form string you can associate with a
615coro. 927coro.
616 928
617This method simply sets the C<< $coro->{desc} >> member to the given 929This method simply sets the C<< $coro->{desc} >> member to the given
618string. You can modify this member directly if you wish, and in fact, this 930string. You can modify this member directly if you wish, and in fact, this
619is often preferred to indicate major processing states that cna then be 931is often preferred to indicate major processing states that cna then be
757 1069
758=back 1070=back
759 1071
760=cut 1072=cut
761 1073
1074for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
1075 my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
1076
1077 *{"Coro::$module\::new"} = sub {
1078 require "Coro/$module.pm";
1079
1080 # some modules have their new predefined in State.xs, some don't
1081 *{"Coro::$module\::new"} = $old
1082 if $old;
1083
1084 goto &{"Coro::$module\::new"};
1085 };
1086}
1087
7621; 10881;
763 1089
764=head1 HOW TO WAIT FOR A CALLBACK 1090=head1 HOW TO WAIT FOR A CALLBACK
765 1091
766It is very common for a coro to wait for some callback to be 1092It is very common for a coro to wait for some callback to be

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