274 lines
8.1 KiB
Perl
274 lines
8.1 KiB
Perl
package Thread;
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use strict;
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use warnings;
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no warnings 'redefine';
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our $VERSION = '3.04';
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$VERSION = eval $VERSION;
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BEGIN {
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use Config;
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if (! $Config{useithreads}) {
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die("This Perl not built to support threads\n");
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}
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}
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use threads 'yield';
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use threads::shared;
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require Exporter;
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our @ISA = qw(Exporter threads);
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our @EXPORT = qw(cond_wait cond_broadcast cond_signal);
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our @EXPORT_OK = qw(async yield);
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sub async (&;@) { return Thread->new(shift); }
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sub done { return ! shift->is_running(); }
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sub eval { die("'eval' not implemented with 'ithreads'\n"); };
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sub flags { die("'flags' not implemented with 'ithreads'\n"); };
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1;
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__END__
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=head1 NAME
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Thread - Manipulate threads in Perl (for old code only)
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=head1 DEPRECATED
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The C<Thread> module served as the frontend to the old-style thread model,
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called I<5005threads>, that was introduced in release 5.005. That model was
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deprecated, and has been removed in version 5.10.
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For old code and interim backwards compatibility, the C<Thread> module has
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been reworked to function as a frontend for the new interpreter threads
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(I<ithreads>) model. However, some previous functionality is not available.
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Further, the data sharing models between the two thread models are completely
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different, and anything to do with data sharing has to be thought differently.
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With I<ithreads>, you must explicitly C<share()> variables between the
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threads.
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You are strongly encouraged to migrate any existing threaded code to the new
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model (i.e., use the C<threads> and C<threads::shared> modules) as soon as
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possible.
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=head1 HISTORY
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In Perl 5.005, the thread model was that all data is implicitly shared, and
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shared access to data has to be explicitly synchronized. This model is called
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I<5005threads>.
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In Perl 5.6, a new model was introduced in which all is was thread local and
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shared access to data has to be explicitly declared. This model is called
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I<ithreads>, for "interpreter threads".
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In Perl 5.6, the I<ithreads> model was not available as a public API; only as
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an internal API that was available for extension writers, and to implement
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fork() emulation on Win32 platforms.
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In Perl 5.8, the I<ithreads> model became available through the C<threads>
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module, and the I<5005threads> model was deprecated.
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In Perl 5.10, the I<5005threads> model was removed from the Perl interpreter.
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=head1 SYNOPSIS
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use Thread qw(:DEFAULT async yield);
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my $t = Thread->new(\&start_sub, @start_args);
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$result = $t->join;
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$t->detach;
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if ($t->done) {
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$t->join;
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}
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if($t->equal($another_thread)) {
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# ...
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}
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yield();
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my $tid = Thread->self->tid;
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lock($scalar);
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lock(@array);
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lock(%hash);
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my @list = Thread->list;
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=head1 DESCRIPTION
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The C<Thread> module provides multithreading support for Perl.
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=head1 FUNCTIONS
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=over 8
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=item $thread = Thread->new(\&start_sub)
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=item $thread = Thread->new(\&start_sub, LIST)
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C<new> starts a new thread of execution in the referenced subroutine. The
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optional list is passed as parameters to the subroutine. Execution
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continues in both the subroutine and the code after the C<new> call.
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C<Thread->new> returns a thread object representing the newly created
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thread.
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=item lock VARIABLE
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C<lock> places a lock on a variable until the lock goes out of scope.
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If the variable is locked by another thread, the C<lock> call will
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block until it's available. C<lock> is recursive, so multiple calls
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to C<lock> are safe--the variable will remain locked until the
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outermost lock on the variable goes out of scope.
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Locks on variables only affect C<lock> calls--they do I<not> affect normal
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access to a variable. (Locks on subs are different, and covered in a bit.)
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If you really, I<really> want locks to block access, then go ahead and tie
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them to something and manage this yourself. This is done on purpose.
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While managing access to variables is a good thing, Perl doesn't force
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you out of its living room...
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If a container object, such as a hash or array, is locked, all the
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elements of that container are not locked. For example, if a thread
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does a C<lock @a>, any other thread doing a C<lock($a[12])> won't
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block.
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Finally, C<lock> will traverse up references exactly I<one> level.
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C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
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=item async BLOCK;
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C<async> creates a thread to execute the block immediately following
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it. This block is treated as an anonymous sub, and so must have a
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semi-colon after the closing brace. Like C<Thread->new>, C<async>
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returns a thread object.
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=item Thread->self
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The C<Thread-E<gt>self> function returns a thread object that represents
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the thread making the C<Thread-E<gt>self> call.
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=item Thread->list
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Returns a list of all non-joined, non-detached Thread objects.
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=item cond_wait VARIABLE
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The C<cond_wait> function takes a B<locked> variable as
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a parameter, unlocks the variable, and blocks until another thread
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does a C<cond_signal> or C<cond_broadcast> for that same locked
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variable. The variable that C<cond_wait> blocked on is relocked
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after the C<cond_wait> is satisfied. If there are multiple threads
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C<cond_wait>ing on the same variable, all but one will reblock waiting
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to re-acquire the lock on the variable. (So if you're only using
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C<cond_wait> for synchronization, give up the lock as soon as
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possible.)
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=item cond_signal VARIABLE
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The C<cond_signal> function takes a locked variable as a parameter and
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unblocks one thread that's C<cond_wait>ing on that variable. If more than
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one thread is blocked in a C<cond_wait> on that variable, only one (and
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which one is indeterminate) will be unblocked.
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If there are no threads blocked in a C<cond_wait> on the variable,
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the signal is discarded.
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=item cond_broadcast VARIABLE
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The C<cond_broadcast> function works similarly to C<cond_signal>.
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C<cond_broadcast>, though, will unblock B<all> the threads that are
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blocked in a C<cond_wait> on the locked variable, rather than only
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one.
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=item yield
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The C<yield> function allows another thread to take control of the
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CPU. The exact results are implementation-dependent.
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=back
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=head1 METHODS
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=over 8
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=item join
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C<join> waits for a thread to end and returns any values the thread
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exited with. C<join> will block until the thread has ended, though
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it won't block if the thread has already terminated.
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If the thread being C<join>ed C<die>d, the error it died with will
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be returned at this time. If you don't want the thread performing
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the C<join> to die as well, you should either wrap the C<join> in
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an C<eval> or use the C<eval> thread method instead of C<join>.
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=item detach
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C<detach> tells a thread that it is never going to be joined i.e.
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that all traces of its existence can be removed once it stops running.
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Errors in detached threads will not be visible anywhere - if you want
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to catch them, you should use $SIG{__DIE__} or something like that.
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=item equal
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C<equal> tests whether two thread objects represent the same thread and
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returns true if they do.
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=item tid
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The C<tid> method returns the tid of a thread. The tid is
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a monotonically increasing integer assigned when a thread is
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created. The main thread of a program will have a tid of zero,
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while subsequent threads will have tids assigned starting with one.
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=item done
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The C<done> method returns true if the thread you're checking has
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finished, and false otherwise.
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=back
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=head1 DEFUNCT
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The following were implemented with I<5005threads>, but are no longer
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available with I<ithreads>.
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=over 8
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=item lock(\&sub)
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With 5005threads, you could also C<lock> a sub such that any calls to that sub
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from another thread would block until the lock was released.
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Also, subroutines could be declared with the C<:locked> attribute which would
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serialize access to the subroutine, but allowed different threads
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non-simultaneous access.
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=item eval
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The C<eval> method wrapped an C<eval> around a C<join>, and so waited for a
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thread to exit, passing along any values the thread might have returned and
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placing any errors into C<$@>.
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=item flags
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The C<flags> method returned the flags for the thread - an integer value
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corresponding to the internal flags for the thread.
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=back
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=head1 SEE ALSO
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L<threads>, L<threads::shared>, L<Thread::Queue>, L<Thread::Semaphore>
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=cut
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