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Revision 1.7 by root, Fri Jul 13 13:05:38 2001 UTC vs.
Revision 1.191 by root, Sat May 31 12:10:55 2008 UTC

1=head1 NAME 1=head1 NAME
2 2
3Coro - create and manage simple coroutines 3Coro - coroutine process abstraction
4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use Coro; 7 use Coro;
8 8
9 $new = new Coro sub { 9 async {
10 print "in coroutine, switching back\n"; 10 # some asynchronous thread of execution
11 $new->transfer($main); 11 print "2\n";
12 print "in coroutine again, switching back\n"; 12 cede; # yield back to main
13 $new->transfer($main); 13 print "4\n";
14 }; 14 };
15 15 print "1\n";
16 $main = new Coro; 16 cede; # yield to coroutine
17 17 print "3\n";
18 print "in main, switching to coroutine\n"; 18 cede; # and again
19 $main->transfer($new); 19
20 print "back in main, switch to coroutine again\n"; 20 # use locking
21 $main->transfer($new); 21 my $lock = new Coro::Semaphore;
22 print "back in main\n"; 22 my $locked;
23
24 $lock->down;
25 $locked = 1;
26 $lock->up;
23 27
24=head1 DESCRIPTION 28=head1 DESCRIPTION
25 29
26This module implements coroutines. Coroutines, similar to continuations, 30This module collection manages coroutines. Coroutines are similar to
27allow you to run more than one "thread of execution" in parallel. Unlike 31threads but don't (in general) run in parallel at the same time even
28threads this, only voluntary switching is used so locking problems are 32on SMP machines. The specific flavor of coroutine used in this module
29greatly reduced. 33also guarantees you that it will not switch between coroutines unless
34necessary, at easily-identified points in your program, so locking and
35parallel access are rarely an issue, making coroutine programming much
36safer and easier than threads programming.
30 37
31Although this is the "main" module of the Coro family it provides only 38Unlike a normal perl program, however, coroutines allow you to have
32low-level functionality. See L<Coro::Process> and related modules for a 39multiple running interpreters that share data, which is especially useful
33more useful process abstraction including scheduling. 40to code pseudo-parallel processes and for event-based programming, such as
41multiple HTTP-GET requests running concurrently. See L<Coro::AnyEvent> to
42learn more.
43
44Coroutines are also useful because Perl has no support for threads (the so
45called "threads" that perl offers are nothing more than the (bad) process
46emulation coming from the Windows platform: On standard operating systems
47they serve no purpose whatsoever, except by making your programs slow and
48making them use a lot of memory. Best disable them when building perl, or
49aks your software vendor/distributor to do it for you).
50
51In this module, coroutines are defined as "callchain + lexical variables +
52@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,
53its own set of lexicals and its own set of perls most important global
54variables (see L<Coro::State> for more configuration).
55
56=cut
57
58package Coro;
59
60use strict;
61no warnings "uninitialized";
62
63use Coro::State;
64
65use base qw(Coro::State Exporter);
66
67our $idle; # idle handler
68our $main; # main coroutine
69our $current; # current coroutine
70
71our $VERSION = 4.742;
72
73our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
74our %EXPORT_TAGS = (
75 prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
76);
77our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
34 78
35=over 4 79=over 4
36 80
37=cut 81=item $Coro::main
38 82
39package Coro; 83This variable stores the coroutine object that represents the main
84program. While you cna C<ready> it and do most other things you can do to
85coroutines, it is mainly useful to compare again C<$Coro::current>, to see
86wether you are running in the main program or not.
40 87
41BEGIN { 88=cut
42 $VERSION = 0.03;
43 89
90$main = new Coro;
91
92=item $Coro::current
93
94The coroutine object representing the current coroutine (the last
95coroutine that the Coro scheduler switched to). The initial value is
96C<$main> (of course).
97
98This variable is B<strictly> I<read-only>. You can take copies of the
99value stored in it and use it as any other coroutine object, but you must
100not otherwise modify the variable itself.
101
102=cut
103
104$main->{desc} = "[main::]";
105
106# maybe some other module used Coro::Specific before...
107$main->{_specific} = $current->{_specific}
108 if $current;
109
110_set_current $main;
111
112sub current() { $current } # [DEPRECATED]
113
114=item $Coro::idle
115
116This variable is mainly useful to integrate Coro into event loops. It is
117usually better to rely on L<Coro::AnyEvent> or LC<Coro::EV>, as this is
118pretty low-level functionality.
119
120This variable stores a callback that is called whenever the scheduler
121finds no ready coroutines to run. The default implementation prints
122"FATAL: deadlock detected" and exits, because the program has no other way
123to continue.
124
125This hook is overwritten by modules such as C<Coro::Timer> and
126C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
127coroutine so the scheduler can run it.
128
129Note that the callback I<must not>, under any circumstances, block
130the current coroutine. Normally, this is achieved by having an "idle
131coroutine" that calls the event loop and then blocks again, and then
132readying that coroutine in the idle handler.
133
134See L<Coro::Event> or L<Coro::AnyEvent> for examples of using this
135technique.
136
137Please note that if your callback recursively invokes perl (e.g. for event
138handlers), then it must be prepared to be called recursively itself.
139
140=cut
141
142$idle = sub {
44 require XSLoader; 143 require Carp;
45 XSLoader::load Coro, $VERSION; 144 Carp::croak ("FATAL: deadlock detected");
46} 145};
47 146
48=item $coro = new [$coderef [, @args]] 147sub _cancel {
148 my ($self) = @_;
49 149
50Create a new coroutine and return it. The first C<transfer> call to this 150 # free coroutine data and mark as destructed
51coroutine will start execution at the given coderef. If, the subroutine 151 $self->_destroy
52returns it will be executed again. 152 or return;
53 153
54If the coderef is omitted this function will create a new "empty" 154 # call all destruction callbacks
55coroutine, i.e. a coroutine that cannot be transfered to but can be used 155 $_->(@{$self->{_status}})
56to save the current coroutine in. 156 for @{(delete $self->{_on_destroy}) || []};
157}
57 158
159# this coroutine is necessary because a coroutine
160# cannot destroy itself.
161my @destroy;
162my $manager;
163
164$manager = new Coro sub {
165 while () {
166 (shift @destroy)->_cancel
167 while @destroy;
168
169 &schedule;
170 }
171};
172$manager->desc ("[coro manager]");
173$manager->prio (PRIO_MAX);
174
175=back
176
177=head2 SIMPLE COROUTINE CREATION
178
179=over 4
180
181=item async { ... } [@args...]
182
183Create a new coroutine and return it's coroutine object (usually
184unused). The coroutine will be put into the ready queue, so
185it will start running automatically on the next scheduler run.
186
187The first argument is a codeblock/closure that should be executed in the
188coroutine. When it returns argument returns the coroutine is automatically
189terminated.
190
191The remaining arguments are passed as arguments to the closure.
192
193See the C<Coro::State::new> constructor for info about the coroutine
194environment in which coroutines are executed.
195
196Calling C<exit> in a coroutine will do the same as calling exit outside
197the coroutine. Likewise, when the coroutine dies, the program will exit,
198just as it would in the main program.
199
200If you do not want that, you can provide a default C<die> handler, or
201simply avoid dieing (by use of C<eval>).
202
203Example: Create a new coroutine that just prints its arguments.
204
205 async {
206 print "@_\n";
207 } 1,2,3,4;
208
58=cut 209=cut
210
211sub async(&@) {
212 my $coro = new Coro @_;
213 $coro->ready;
214 $coro
215}
216
217=item async_pool { ... } [@args...]
218
219Similar to C<async>, but uses a coroutine pool, so you should not call
220terminate or join on it (although you are allowed to), and you get a
221coroutine that might have executed other code already (which can be good
222or bad :).
223
224On the plus side, this function is faster than creating (and destroying)
225a completely new coroutine, so if you need a lot of generic coroutines in
226quick successsion, use C<async_pool>, not C<async>.
227
228The code block is executed in an C<eval> context and a warning will be
229issued in case of an exception instead of terminating the program, as
230C<async> does. As the coroutine is being reused, stuff like C<on_destroy>
231will not work in the expected way, unless you call terminate or cancel,
232which somehow defeats the purpose of pooling (but is fine in the
233exceptional case).
234
235The priority will be reset to C<0> after each run, tracing will be
236disabled, the description will be reset and the default output filehandle
237gets restored, so you can change all these. Otherwise the coroutine will
238be re-used "as-is": most notably if you change other per-coroutine global
239stuff such as C<$/> you I<must needs> to revert that change, which is most
240simply done by using local as in: C< local $/ >.
241
242The pool size is limited to C<8> idle coroutines (this can be adjusted by
243changing $Coro::POOL_SIZE), and there can be as many non-idle coros as
244required.
245
246If you are concerned about pooled coroutines growing a lot because a
247single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
248{ terminate }> once per second or so to slowly replenish the pool. In
249addition to that, when the stacks used by a handler grows larger than 16kb
250(adjustable via $Coro::POOL_RSS) it will also be destroyed.
251
252=cut
253
254our $POOL_SIZE = 8;
255our $POOL_RSS = 16 * 1024;
256our @async_pool;
257
258sub pool_handler {
259 my $cb;
260
261 while () {
262 eval {
263 while () {
264 _pool_1 $cb;
265 &$cb;
266 _pool_2 $cb;
267 &schedule;
268 }
269 };
270
271 last if $@ eq "\3async_pool terminate\2\n";
272 warn $@ if $@;
273 }
274}
275
276sub async_pool(&@) {
277 # this is also inlined into the unlock_scheduler
278 my $coro = (pop @async_pool) || new Coro \&pool_handler;
279
280 $coro->{_invoke} = [@_];
281 $coro->ready;
282
283 $coro
284}
285
286=back
287
288=head2 STATIC METHODS
289
290Static methods are actually functions that operate on the current coroutine.
291
292=over 4
293
294=item schedule
295
296Calls the scheduler. The scheduler will find the next coroutine that is
297to be run from the ready queue and switches to it. The next coroutine
298to be run is simply the one with the highest priority that is longest
299in its ready queue. If there is no coroutine ready, it will clal the
300C<$Coro::idle> hook.
301
302Please note that the current coroutine will I<not> be put into the ready
303queue, so calling this function usually means you will never be called
304again unless something else (e.g. an event handler) calls C<< ->ready >>,
305thus waking you up.
306
307This makes C<schedule> I<the> generic method to use to block the current
308coroutine and wait for events: first you remember the current coroutine in
309a variable, then arrange for some callback of yours to call C<< ->ready
310>> on that once some event happens, and last you call C<schedule> to put
311yourself to sleep. Note that a lot of things can wake your coroutine up,
312so you need to check wether the event indeed happened, e.g. by storing the
313status in a variable.
314
315The canonical way to wait on external events is this:
316
317 {
318 # remember current coroutine
319 my $current = $Coro::current;
320
321 # register a hypothetical event handler
322 on_event_invoke sub {
323 # wake up sleeping coroutine
324 $current->ready;
325 undef $current;
326 };
327
328 # call schedule until event occurred.
329 # in case we are woken up for other reasons
330 # (current still defined), loop.
331 Coro::schedule while $current;
332 }
333
334=item cede
335
336"Cede" to other coroutines. This function puts the current coroutine into
337the ready queue and calls C<schedule>, which has the effect of giving
338up the current "timeslice" to other coroutines of the same or higher
339priority. Once your coroutine gets its turn again it will automatically be
340resumed.
341
342This function is often called C<yield> in other languages.
343
344=item Coro::cede_notself
345
346Works like cede, but is not exported by default and will cede to I<any>
347coroutine, regardless of priority. This is useful sometimes to ensure
348progress is made.
349
350=item terminate [arg...]
351
352Terminates the current coroutine with the given status values (see L<cancel>).
353
354=item killall
355
356Kills/terminates/cancels all coroutines except the currently running
357one. This is useful after a fork, either in the child or the parent, as
358usually only one of them should inherit the running coroutines.
359
360Note that while this will try to free some of the main programs resources,
361you cnanot free all of them, so if a coroutine that is not the main
362program calls this function, there will be some one-time resource leak.
363
364=cut
365
366sub terminate {
367 $current->cancel (@_);
368}
369
370sub killall {
371 for (Coro::State::list) {
372 $_->cancel
373 if $_ != $current && UNIVERSAL::isa $_, "Coro";
374 }
375}
376
377=back
378
379=head2 COROUTINE METHODS
380
381These are the methods you can call on coroutine objects (or to create
382them).
383
384=over 4
385
386=item new Coro \&sub [, @args...]
387
388Create a new coroutine and return it. When the sub returns, the coroutine
389automatically terminates as if C<terminate> with the returned values were
390called. To make the coroutine run you must first put it into the ready
391queue by calling the ready method.
392
393See C<async> and C<Coro::State::new> for additional info about the
394coroutine environment.
395
396=cut
397
398sub _run_coro {
399 terminate &{+shift};
400}
59 401
60sub new { 402sub new {
61 my $class = $_[0]; 403 my $class = shift;
62 my $proc = $_[1] || sub { die "tried to transfer to an empty coroutine" };
63 bless _newprocess {
64 do {
65 eval { &$proc };
66 if ($@) {
67 $error_msg = $@;
68 $error_coro = _newprocess { };
69 &transfer($error_coro, $error);
70 }
71 } while (1);
72 }, $class;
73}
74 404
75=item $prev->transfer($next) 405 $class->SUPER::new (\&_run_coro, @_)
406}
76 407
77Save the state of the current subroutine in C<$prev> and switch to the 408=item $success = $coroutine->ready
78coroutine saved in C<$next>.
79 409
80The "state" of a subroutine only ever includes scope, i.e. lexical 410Put the given coroutine into the end of its ready queue (there is one
81variables and the current execution state. It does not save/restore any 411queue for each priority) and return true. If the coroutine is already in
82global variables such as C<$_> or C<$@> or any other special or non 412the ready queue, do nothing and return false.
83special variables. So remember that every function call that might call
84C<transfer> (such as C<Coro::Channel::put>) might clobber any global
85and/or special variables. Yes, this is by design ;) You cna always create
86your own process abstraction model that saves these variables.
87 413
88The easiest way to do this is to create your own scheduling primitive like this: 414This ensures that the scheduler will resume this coroutine automatically
415once all the coroutines of higher priority and all coroutines of the same
416priority that were put into the ready queue earlier have been resumed.
89 417
90 sub schedule { 418=item $is_ready = $coroutine->is_ready
91 local ($_, $@, ...); 419
92 $old->transfer($new); 420Return wether the coroutine is currently the ready queue or not,
421
422=item $coroutine->cancel (arg...)
423
424Terminates the given coroutine and makes it return the given arguments as
425status (default: the empty list). Never returns if the coroutine is the
426current coroutine.
427
428=cut
429
430sub cancel {
431 my $self = shift;
432 $self->{_status} = [@_];
433
434 if ($current == $self) {
435 push @destroy, $self;
436 $manager->ready;
437 &schedule while 1;
438 } else {
439 $self->_cancel;
93 } 440 }
94
95=cut
96
97# I call the _transfer function from a perl function
98# because that way perl saves all important things on
99# the stack. Actually, I'd do it from within XS, but
100# I couldn't get it to work.
101sub transfer {
102 _transfer($_[0], $_[1]);
103} 441}
104 442
105=item $error, $error_msg, $error_coro 443=item $coroutine->join
106 444
107This coroutine will be called on fatal errors. C<$error_msg> and 445Wait until the coroutine terminates and return any values given to the
108C<$error_coro> return the error message and the error-causing coroutine 446C<terminate> or C<cancel> functions. C<join> can be called concurrently
109(NOT an object) respectively. This API might change. 447from multiple coroutines, and all will be resumed and given the status
448return once the C<$coroutine> terminates.
110 449
111=cut 450=cut
112 451
113$error_msg = 452sub join {
114$error_coro = undef; 453 my $self = shift;
115 454
116$error = _newprocess { 455 unless ($self->{_status}) {
117 print STDERR "FATAL: $error_msg\nprogram aborted\n"; 456 my $current = $current;
118 exit 50; 457
458 push @{$self->{_on_destroy}}, sub {
459 $current->ready;
460 undef $current;
461 };
462
463 &schedule while $current;
464 }
465
466 wantarray ? @{$self->{_status}} : $self->{_status}[0];
467}
468
469=item $coroutine->on_destroy (\&cb)
470
471Registers a callback that is called when this coroutine gets destroyed,
472but before it is joined. The callback gets passed the terminate arguments,
473if any, and I<must not> die, under any circumstances.
474
475=cut
476
477sub on_destroy {
478 my ($self, $cb) = @_;
479
480 push @{ $self->{_on_destroy} }, $cb;
481}
482
483=item $oldprio = $coroutine->prio ($newprio)
484
485Sets (or gets, if the argument is missing) the priority of the
486coroutine. Higher priority coroutines get run before lower priority
487coroutines. Priorities are small signed integers (currently -4 .. +3),
488that you can refer to using PRIO_xxx constants (use the import tag :prio
489to get then):
490
491 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
492 3 > 1 > 0 > -1 > -3 > -4
493
494 # set priority to HIGH
495 current->prio(PRIO_HIGH);
496
497The idle coroutine ($Coro::idle) always has a lower priority than any
498existing coroutine.
499
500Changing the priority of the current coroutine will take effect immediately,
501but changing the priority of coroutines in the ready queue (but not
502running) will only take effect after the next schedule (of that
503coroutine). This is a bug that will be fixed in some future version.
504
505=item $newprio = $coroutine->nice ($change)
506
507Similar to C<prio>, but subtract the given value from the priority (i.e.
508higher values mean lower priority, just as in unix).
509
510=item $olddesc = $coroutine->desc ($newdesc)
511
512Sets (or gets in case the argument is missing) the description for this
513coroutine. This is just a free-form string you can associate with a coroutine.
514
515This method simply sets the C<< $coroutine->{desc} >> member to the given string. You
516can modify this member directly if you wish.
517
518=item $coroutine->throw ([$scalar])
519
520If C<$throw> is specified and defined, it will be thrown as an exception
521inside the coroutine at the next convinient point in time (usually after
522it gains control at the next schedule/transfer/cede). Otherwise clears the
523exception object.
524
525The exception object will be thrown "as is" with the specified scalar in
526C<$@>, i.e. if it is a string, no line number or newline will be appended
527(unlike with C<die>).
528
529This can be used as a softer means than C<cancel> to ask a coroutine to
530end itself, although there is no guarentee that the exception will lead to
531termination, and if the exception isn't caught it might well end the whole
532program.
533
534=cut
535
536sub desc {
537 my $old = $_[0]{desc};
538 $_[0]{desc} = $_[1] if @_ > 1;
539 $old;
540}
541
542=back
543
544=head2 GLOBAL FUNCTIONS
545
546=over 4
547
548=item Coro::nready
549
550Returns the number of coroutines that are currently in the ready state,
551i.e. that can be switched to by calling C<schedule> directory or
552indirectly. The value C<0> means that the only runnable coroutine is the
553currently running one, so C<cede> would have no effect, and C<schedule>
554would cause a deadlock unless there is an idle handler that wakes up some
555coroutines.
556
557=item my $guard = Coro::guard { ... }
558
559This creates and returns a guard object. Nothing happens until the object
560gets destroyed, in which case the codeblock given as argument will be
561executed. This is useful to free locks or other resources in case of a
562runtime error or when the coroutine gets canceled, as in both cases the
563guard block will be executed. The guard object supports only one method,
564C<< ->cancel >>, which will keep the codeblock from being executed.
565
566Example: set some flag and clear it again when the coroutine gets canceled
567or the function returns:
568
569 sub do_something {
570 my $guard = Coro::guard { $busy = 0 };
571 $busy = 1;
572
573 # do something that requires $busy to be true
574 }
575
576=cut
577
578sub guard(&) {
579 bless \(my $cb = $_[0]), "Coro::guard"
580}
581
582sub Coro::guard::cancel {
583 ${$_[0]} = sub { };
584}
585
586sub Coro::guard::DESTROY {
587 ${$_[0]}->();
588}
589
590
591=item unblock_sub { ... }
592
593This utility function takes a BLOCK or code reference and "unblocks" it,
594returning a new coderef. Unblocking means that calling the new coderef
595will return immediately without blocking, returning nothing, while the
596original code ref will be called (with parameters) from within another
597coroutine.
598
599The reason this function exists is that many event libraries (such as the
600venerable L<Event|Event> module) are not coroutine-safe (a weaker form
601of thread-safety). This means you must not block within event callbacks,
602otherwise you might suffer from crashes or worse. The only event library
603currently known that is safe to use without C<unblock_sub> is L<EV>.
604
605This function allows your callbacks to block by executing them in another
606coroutine where it is safe to block. One example where blocking is handy
607is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
608disk, for example.
609
610In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
611creating event callbacks that want to block.
612
613If your handler does not plan to block (e.g. simply sends a message to
614another coroutine, or puts some other coroutine into the ready queue),
615there is no reason to use C<unblock_sub>.
616
617Note that you also need to use C<unblock_sub> for any other callbacks that
618are indirectly executed by any C-based event loop. For example, when you
619use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
620provides callbacks that are the result of some event callback, then you
621must not block either, or use C<unblock_sub>.
622
623=cut
624
625our @unblock_queue;
626
627# we create a special coro because we want to cede,
628# to reduce pressure on the coro pool (because most callbacks
629# return immediately and can be reused) and because we cannot cede
630# inside an event callback.
631our $unblock_scheduler = new Coro sub {
632 while () {
633 while (my $cb = pop @unblock_queue) {
634 # this is an inlined copy of async_pool
635 my $coro = (pop @async_pool) || new Coro \&pool_handler;
636
637 $coro->{_invoke} = $cb;
638 $coro->ready;
639 cede; # for short-lived callbacks, this reduces pressure on the coro pool
640 }
641 schedule; # sleep well
642 }
119}; 643};
644$unblock_scheduler->desc ("[unblock_sub scheduler]");
645
646sub unblock_sub(&) {
647 my $cb = shift;
648
649 sub {
650 unshift @unblock_queue, [$cb, @_];
651 $unblock_scheduler->ready;
652 }
653}
654
655=back
656
657=cut
120 658
1211; 6591;
122 660
123=back 661=head1 BUGS/LIMITATIONS
124 662
125=head1 BUGS 663This module is not perl-pseudo-thread-safe. You should only ever use this
126 664module from the same thread (this requirement might be removed in the
127This module has not yet been extensively tested. 665future to allow per-thread schedulers, but Coro::State does not yet allow
666this). I recommend disabling thread support and using processes, as this
667is much faster and uses less memory.
128 668
129=head1 SEE ALSO 669=head1 SEE ALSO
130 670
131L<Coro::Process>, L<Coro::Signal>. 671Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
672
673Debugging: L<Coro::Debug>.
674
675Support/Utility: L<Coro::Specific>, L<Coro::Util>.
676
677Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.
678
679IO/Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
680
681Compatibility: L<Coro::LWP>, L<Coro::BDB>, L<Coro::Storable>, L<Coro::Select>.
682
683XS API: L<Coro::MakeMaker>.
684
685Low level Configuration, Coroutine Environment: L<Coro::State>.
132 686
133=head1 AUTHOR 687=head1 AUTHOR
134 688
135 Marc Lehmann <pcg@goof.com> 689 Marc Lehmann <schmorp@schmorp.de>
136 http://www.goof.com/pcg/marc/ 690 http://home.schmorp.de/
137 691
138=cut 692=cut
139 693

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