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225 lines
7.3 KiB
225 lines
7.3 KiB
package Thread;
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require Exporter;
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use XSLoader ();
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our($VERSION, @ISA, @EXPORT);
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$VERSION = "1.0";
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@ISA = qw(Exporter);
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@EXPORT_OK = qw(yield cond_signal cond_broadcast cond_wait async);
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=head1 NAME
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Thread - manipulate threads in Perl (EXPERIMENTAL, subject to change)
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=head1 CAVEAT
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The Thread extension requires Perl to be built in a particular way to
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enable the older 5.005 threading model. Just to confuse matters, there
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is an alternate threading model known as "ithreads" that does NOT
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support this extension. If you are using a binary distribution such
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as ActivePerl that is built with ithreads support, this extension CANNOT
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be used.
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=head1 SYNOPSIS
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use Thread;
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my $t = new Thread \&start_sub, @start_args;
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$result = $t->join;
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$result = $t->eval;
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$t->detach;
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if($t->equal($another_thread)) {
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# ...
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}
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my $tid = Thread->self->tid;
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my $tlist = Thread->list;
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lock($scalar);
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yield();
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use Thread 'async';
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=head1 DESCRIPTION
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WARNING: Threading is an experimental feature. Both the interface
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and implementation are subject to change drastically. In fact, this
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documentation describes the flavor of threads that was in version
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5.005. Perl 5.6.0 and later have the beginnings of support for
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interpreter threads, which (when finished) is expected to be
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significantly different from what is described here. The information
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contained here may therefore soon be obsolete. Use at your own risk!
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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 new \&start_sub
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=item 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<new Thread> 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. If
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the variable is locked by another thread, the C<lock> call will block until
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it's available. C<lock> is recursive, so multiple calls to C<lock> are
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safe--the variable will remain locked until the outermost lock on the
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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. While
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managing access to variables is a good thing, perl doesn't force you out of
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its living room...
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If a container object, such as a hash or array, is locked, all the elements
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of that container are not locked. For example, if a thread does a C<lock
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@a>, any other thread doing a C<lock($a[12])> won't block.
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You may also C<lock> a sub, using C<lock &sub>. Any calls to that sub from
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another thread will block until the lock is released. This behaviour is not
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equivalent to declaring the sub with the C<locked> attribute. The C<locked>
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attribute serializes access to a subroutine, but allows different threads
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non-simultaneous access. C<lock &sub>, on the other hand, will not allow
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I<any> other thread access for the duration of the lock.
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Finally, C<lock> will traverse up references exactly I<one> level.
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C<lock(\$a)> is equivalent to C<lock($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<new Thread>, C<async> returns a
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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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C<Thread-E<gt>list> returns a list of thread objects for all running and
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finished but un-C<join>ed threads.
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=item cond_wait VARIABLE
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The C<cond_wait> function takes a B<locked> variable as a parameter,
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unlocks the variable, and blocks until another thread does a C<cond_signal>
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or C<cond_broadcast> for that same locked variable. The variable that
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C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied.
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If there are multiple threads C<cond_wait>ing on the same variable, all but
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one will reblock waiting to reaquire the lock on the variable. (So if
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you're only using C<cond_wait> for synchronization, give up the lock as
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soon as 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, the
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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 blocked
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in a C<cond_wait> on the locked variable, rather than only 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 exited
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with. C<join> will block until the thread has ended, though it won't block
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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 be
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returned at this time. If you don't want the thread performing the C<join>
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to die as well, you should either wrap the C<join> in an C<eval> or use the
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C<eval> thread method instead of C<join>.
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=item eval
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The C<eval> method wraps an C<eval> around a C<join>, and so waits for a
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thread to exit, passing along any values the thread might have returned.
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Errors, of course, get placed into C<$@>.
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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 a monotonically
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increasing integer assigned when a thread is created. The main thread of a
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program will have a tid of zero, while subsequent threads will have tids
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assigned starting with one.
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=back
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=head1 LIMITATIONS
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The sequence number used to assign tids is a simple integer, and no
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checking is done to make sure the tid isn't currently in use. If a program
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creates more than 2^32 - 1 threads in a single run, threads may be assigned
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duplicate tids. This limitation may be lifted in a future version of Perl.
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=head1 SEE ALSO
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L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>, L<Thread::Specific>.
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=cut
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#
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# Methods
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#
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#
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# Exported functions
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#
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sub async (&) {
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return new Thread $_[0];
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}
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sub eval {
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return eval { shift->join; };
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}
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XSLoader::load 'Thread';
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1;
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