perl/lib/Thread.pm

package Thread;

use strict;

our($VERSION, $ithreads, $othreads);

BEGIN {
    $VERSION = '2.00';
    use Config;
    $ithreads = $Config{useithreads};
    $othreads = $Config{use5005threads};
}

require Exporter;
use XSLoader ();
our(@ISA, @EXPORT, @EXPORT_OK);

@ISA = qw(Exporter);

BEGIN {
    if ($ithreads) {
        @EXPORT = qw(cond_wait cond_broadcast cond_signal)
    } elsif ($othreads) {
        @EXPORT_OK = qw(cond_signal cond_broadcast cond_wait);
    }
    push @EXPORT_OK, qw(async yield);
}

=head1 NAME

Thread - manipulate threads in Perl (for old code only)

=head1 CAVEAT

Perl has two thread models.

In Perl 5.005 the thread model was that all data is implicitly shared
and shared access to data has to be explicitly synchronized.
This model is called "5005threads".

In Perl 5.6 a new model was introduced in which all is was thread
local and shared access to data has to be explicitly declared.
This model is called "ithreads", for "interpreter threads".

In Perl 5.6 the ithreads model was not available as a public API,
only as an internal API that was available for extension writers,
and to implement fork() emulation on Win32 platforms.

In Perl 5.8 the ithreads model became available through the C<threads>
module.

Neither model is configured by default into Perl (except, as mentioned
above, in Win32 ithreads are always available.)  You can see your
Perl's threading configuration by running C<perl -V> and looking for
the I<use...threads> variables, or inside script by C<use Config;>
and testing for C<$Config{use5005threads}> and C<$Config{useithreads}>.

For old code and interim backwards compatibility, the Thread module
has been reworked to function as a frontend for both 5005threads and
ithreads.

Note that the compatibility is not complete: because the data sharing
models are directly opposed, anything to do with data sharing has to
be thought differently.  With the ithreads you must explicitly share()
variables between the threads.

For new code the use of the C<Thread> module is discouraged and
the direct use of the C<threads> and C<threads::shared> modules
is encouraged instead.

Finally, note that there are many known serious problems with the
5005threads, one of the least of which is that regular expression
match variables like $1 are not threadsafe, that is, they easily get
corrupted by competing threads.  Other problems include more insidious
data corruption and mysterious crashes.  You are seriously urged to
use ithreads instead.

=head1 SYNOPSIS

    use Thread;

    my $t = Thread->new(\&start_sub, @start_args);

    $result = $t->join;
    $result = $t->eval;
    $t->detach;

    if ($t->done) {
        $t->join;
    }

    if($t->equal($another_thread)) {
        # ...
    }

    yield();

    my $tid = Thread->self->tid; 

    lock($scalar);
    lock(@array);
    lock(%hash);

    lock(\&sub);        # not available with ithreads

    $flags = $t->flags; # not available with ithreads

    my @list = Thread->list;    # not available with ithreads

    use Thread 'async';

=head1 DESCRIPTION

The C<Thread> module provides multithreading support for perl.

=head1 FUNCTIONS

=over 8

=item $thread = Thread->new(\&start_sub)

=item $thread = Thread->new(\&start_sub, LIST)

C<new> starts a new thread of execution in the referenced subroutine. The
optional list is passed as parameters to the subroutine. Execution
continues in both the subroutine and the code after the C<new> call.

C<Thread-&gt;new> returns a thread object representing the newly created
thread.

=item lock VARIABLE

C<lock> places a lock on a variable until the lock goes out of scope.

If the variable is locked by another thread, the C<lock> call will
block until it's available.  C<lock> is recursive, so multiple calls
to C<lock> are safe--the variable will remain locked until the
outermost lock on the variable goes out of scope.

Locks on variables only affect C<lock> calls--they do I<not> affect normal
access to a variable. (Locks on subs are different, and covered in a bit.)
If you really, I<really> want locks to block access, then go ahead and tie
them to something and manage this yourself.  This is done on purpose.
While managing access to variables is a good thing, Perl doesn't force
you out of its living room...

If a container object, such as a hash or array, is locked, all the
elements of that container are not locked. For example, if a thread
does a C<lock @a>, any other thread doing a C<lock($a[12])> won't
block.

With 5005threads you may also C<lock> a sub, using C<lock &sub>.
Any calls to that sub from another thread will block until the lock
is released. This behaviour is not equivalent to declaring the sub
with the C<locked> attribute.  The C<locked> attribute serializes
access to a subroutine, but allows different threads non-simultaneous
access. C<lock &sub>, on the other hand, will not allow I<any> other
thread access for the duration of the lock.

Finally, C<lock> will traverse up references exactly I<one> level.
C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.

=item async BLOCK;

C<async> creates a thread to execute the block immediately following
it.  This block is treated as an anonymous sub, and so must have a
semi-colon after the closing brace. Like C<Thread-&gt;new>, C<async>
returns a thread object.

=item Thread->self

The C<Thread-E<gt>self> function returns a thread object that represents
the thread making the C<Thread-E<gt>self> call.

=item cond_wait VARIABLE

The C<cond_wait> function takes a B<locked> variable as
a parameter, unlocks the variable, and blocks until another thread
does a C<cond_signal> or C<cond_broadcast> for that same locked
variable. The variable that C<cond_wait> blocked on is relocked
after the C<cond_wait> is satisfied.  If there are multiple threads
C<cond_wait>ing on the same variable, all but one will reblock waiting
to reaquire the lock on the variable.  (So if you're only using
C<cond_wait> for synchronization, give up the lock as soon as
possible.)

=item cond_signal VARIABLE

The C<cond_signal> function takes a locked variable as a parameter and
unblocks one thread that's C<cond_wait>ing on that variable. If more than
one thread is blocked in a C<cond_wait> on that variable, only one (and
which one is indeterminate) will be unblocked.

If there are no threads blocked in a C<cond_wait> on the variable,
the signal is discarded.

=item cond_broadcast VARIABLE

The C<cond_broadcast> function works similarly to C<cond_signal>.
C<cond_broadcast>, though, will unblock B<all> the threads that are
blocked in a C<cond_wait> on the locked variable, rather than only
one.

=item yield

The C<yield> function allows another thread to take control of the
CPU. The exact results are implementation-dependent.

=back

=head1 METHODS

=over 8

=item join

C<join> waits for a thread to end and returns any values the thread
exited with.  C<join> will block until the thread has ended, though
it won't block if the thread has already terminated.

If the thread being C<join>ed C<die>d, the error it died with will
be returned at this time. If you don't want the thread performing
the C<join> to die as well, you should either wrap the C<join> in
an C<eval> or use the C<eval> thread method instead of C<join>.

=item eval

The C<eval> method wraps an C<eval> around a C<join>, and so waits for
a thread to exit, passing along any values the thread might have returned.
Errors, of course, get placed into C<$@>.  (Not available with ithreads.)

=item detach

C<detach> tells a thread that it is never going to be joined i.e.
that all traces of its existence can be removed once it stops running.
Errors in detached threads will not be visible anywhere - if you want
to catch them, you should use $SIG{__DIE__} or something like that.

=item equal 

C<equal> tests whether two thread objects represent the same thread and
returns true if they do.

=item tid

The C<tid> method returns the tid of a thread. The tid is
a monotonically increasing integer assigned when a thread is
created. The main thread of a program will have a tid of zero,
while subsequent threads will have tids assigned starting with one.

=item flags

The C<flags> method returns the flags for the thread. This is the
integer value corresponding to the internal flags for the thread,
and the value may not be all that meaningful to you.
(Not available with ithreads.)

=item done

The C<done> method returns true if the thread you're checking has
finished, and false otherwise.  (Not available with ithreads.)

=back

=head1 LIMITATIONS

The sequence number used to assign tids is a simple integer, and no
checking is done to make sure the tid isn't currently in use.  If a
program creates more than 2**32 - 1 threads in a single run, threads
may be assigned duplicate tids.  This limitation may be lifted in
a future version of Perl.

=head1 SEE ALSO

L<threads::shared> (not available with 5005threads)

L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>,
L<Thread::Specific> (not available with ithreads)

=cut

#
# Methods
#

#
# Exported functions
#

sub async (&) {
    return Thread->new($_[0]);
}

sub eval {
    return eval { shift->join; };
}

sub unimplemented {
    print $_[0], " unimplemented with ",
          $Config{useithreads} ? "ithreads" : "5005threads", "\n";

}

sub unimplement {
    for my $m (@_) {
        no strict 'refs';
        *{"Thread::$m"} = sub { unimplemented $m };
    }
}

BEGIN {
    if ($ithreads) {
        if ($othreads) {
            require Carp;
            Carp::croak("This Perl has both ithreads and 5005threads (serious malconfiguration)");
        }
        XSLoader::load 'threads';
        for my $m (qw(new join detach yield self tid equal list)) {
            no strict 'refs';
            *{"Thread::$m"} = \&{"threads::$m"};
        }
        require 'threads/shared.pm';
        for my $m (qw(cond_signal cond_broadcast cond_wait)) {
            no strict 'refs';
            *{"Thread::$m"} = \&{"threads::shared::${m}_enabled"};
        }
        # trying to unimplement eval gives redefined warning
        unimplement(qw(done flags));
    } elsif ($othreads) {
        XSLoader::load 'Thread';
    } else {
        require Carp;
        Carp::croak("This Perl has neither ithreads nor 5005threads");
    }
}

1;
Revision:	1.1
Committed:	Thu Jun 30 14:27:08 2005 UTC (21 years, 3 months ago) by root
Branch:	MAIN
CVS Tags:	PERL-5-8-7, HEAD
Branch point for:	PERL
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	package Thread;
2
3			use strict;
4
5			our($VERSION, $ithreads, $othreads);
6
7			BEGIN {
8			$VERSION = '2.00';
9			use Config;
10			$ithreads = $Config{useithreads};
11			$othreads = $Config{use5005threads};
12			}
13
14			require Exporter;
15			use XSLoader ();
16			our(@ISA, @EXPORT, @EXPORT_OK);
17
18			@ISA = qw(Exporter);
19
20			BEGIN {
21			if ($ithreads) {
22			@EXPORT = qw(cond_wait cond_broadcast cond_signal)
23			} elsif ($othreads) {
24			@EXPORT_OK = qw(cond_signal cond_broadcast cond_wait);
25			}
26			push @EXPORT_OK, qw(async yield);
27			}
28
29			=head1 NAME
30
31			Thread - manipulate threads in Perl (for old code only)
32
33			=head1 CAVEAT
34
35			Perl has two thread models.
36
37			In Perl 5.005 the thread model was that all data is implicitly shared
38			and shared access to data has to be explicitly synchronized.
39			This model is called "5005threads".
40
41			In Perl 5.6 a new model was introduced in which all is was thread
42			local and shared access to data has to be explicitly declared.
43			This model is called "ithreads", for "interpreter threads".
44
45			In Perl 5.6 the ithreads model was not available as a public API,
46			only as an internal API that was available for extension writers,
47			and to implement fork() emulation on Win32 platforms.
48
49			In Perl 5.8 the ithreads model became available through the C<threads>
50			module.
51
52			Neither model is configured by default into Perl (except, as mentioned
53			above, in Win32 ithreads are always available.) You can see your
54			Perl's threading configuration by running C<perl -V> and looking for
55			the I<use...threads> variables, or inside script by C<use Config;>
56			and testing for C<$Config{use5005threads}> and C<$Config{useithreads}>.
57
58			For old code and interim backwards compatibility, the Thread module
59			has been reworked to function as a frontend for both 5005threads and
60			ithreads.
61
62			Note that the compatibility is not complete: because the data sharing
63			models are directly opposed, anything to do with data sharing has to
64			be thought differently. With the ithreads you must explicitly share()
65			variables between the threads.
66
67			For new code the use of the C<Thread> module is discouraged and
68			the direct use of the C<threads> and C<threads::shared> modules
69			is encouraged instead.
70
71			Finally, note that there are many known serious problems with the
72			5005threads, one of the least of which is that regular expression
73			match variables like $1 are not threadsafe, that is, they easily get
74			corrupted by competing threads. Other problems include more insidious
75			data corruption and mysterious crashes. You are seriously urged to
76			use ithreads instead.
77
78			=head1 SYNOPSIS
79
80			use Thread;
81
82			my $t = Thread->new(\&start_sub, @start_args);
83
84			$result = $t->join;
85			$result = $t->eval;
86			$t->detach;
87
88			if ($t->done) {
89			$t->join;
90			}
91
92			if($t->equal($another_thread)) {
93			# ...
94			}
95
96			yield();
97
98			my $tid = Thread->self->tid;
99
100			lock($scalar);
101			lock(@array);
102			lock(%hash);
103
104			lock(\&sub); # not available with ithreads
105
106			$flags = $t->flags; # not available with ithreads
107
108			my @list = Thread->list; # not available with ithreads
109
110			use Thread 'async';
111
112			=head1 DESCRIPTION
113
114			The C<Thread> module provides multithreading support for perl.
115
116			=head1 FUNCTIONS
117
118			=over 8
119
120			=item $thread = Thread->new(\&start_sub)
121
122			=item $thread = Thread->new(\&start_sub, LIST)
123
124			C<new> starts a new thread of execution in the referenced subroutine. The
125			optional list is passed as parameters to the subroutine. Execution
126			continues in both the subroutine and the code after the C<new> call.
127
128			C<Thread->new> returns a thread object representing the newly created
129			thread.
130
131			=item lock VARIABLE
132
133			C<lock> places a lock on a variable until the lock goes out of scope.
134
135			If the variable is locked by another thread, the C<lock> call will
136			block until it's available. C<lock> is recursive, so multiple calls
137			to C<lock> are safe--the variable will remain locked until the
138			outermost lock on the variable goes out of scope.
139
140			Locks on variables only affect C<lock> calls--they do I<not> affect normal
141			access to a variable. (Locks on subs are different, and covered in a bit.)
142			If you really, I<really> want locks to block access, then go ahead and tie
143			them to something and manage this yourself. This is done on purpose.
144			While managing access to variables is a good thing, Perl doesn't force
145			you out of its living room...
146
147			If a container object, such as a hash or array, is locked, all the
148			elements of that container are not locked. For example, if a thread
149			does a C<lock @a>, any other thread doing a C<lock($a[12])> won't
150			block.
151
152			With 5005threads you may also C<lock> a sub, using C<lock &sub>.
153			Any calls to that sub from another thread will block until the lock
154			is released. This behaviour is not equivalent to declaring the sub
155			with the C<locked> attribute. The C<locked> attribute serializes
156			access to a subroutine, but allows different threads non-simultaneous
157			access. C<lock &sub>, on the other hand, will not allow I<any> other
158			thread access for the duration of the lock.
159
160			Finally, C<lock> will traverse up references exactly I<one> level.
161			C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
162
163			=item async BLOCK;
164
165			C<async> creates a thread to execute the block immediately following
166			it. This block is treated as an anonymous sub, and so must have a
167			semi-colon after the closing brace. Like C<Thread->new>, C<async>
168			returns a thread object.
169
170			=item Thread->self
171
172			The C<Thread-E<gt>self> function returns a thread object that represents
173			the thread making the C<Thread-E<gt>self> call.
174
175			=item cond_wait VARIABLE
176
177			The C<cond_wait> function takes a B<locked> variable as
178			a parameter, unlocks the variable, and blocks until another thread
179			does a C<cond_signal> or C<cond_broadcast> for that same locked
180			variable. The variable that C<cond_wait> blocked on is relocked
181			after the C<cond_wait> is satisfied. If there are multiple threads
182			C<cond_wait>ing on the same variable, all but one will reblock waiting
183			to reaquire the lock on the variable. (So if you're only using
184			C<cond_wait> for synchronization, give up the lock as soon as
185			possible.)
186
187			=item cond_signal VARIABLE
188
189			The C<cond_signal> function takes a locked variable as a parameter and
190			unblocks one thread that's C<cond_wait>ing on that variable. If more than
191			one thread is blocked in a C<cond_wait> on that variable, only one (and
192			which one is indeterminate) will be unblocked.
193
194			If there are no threads blocked in a C<cond_wait> on the variable,
195			the signal is discarded.
196
197			=item cond_broadcast VARIABLE
198
199			The C<cond_broadcast> function works similarly to C<cond_signal>.
200			C<cond_broadcast>, though, will unblock B<all> the threads that are
201			blocked in a C<cond_wait> on the locked variable, rather than only
202			one.
203
204			=item yield
205
206			The C<yield> function allows another thread to take control of the
207			CPU. The exact results are implementation-dependent.
208
209			=back
210
211			=head1 METHODS
212
213			=over 8
214
215			=item join
216
217			C<join> waits for a thread to end and returns any values the thread
218			exited with. C<join> will block until the thread has ended, though
219			it won't block if the thread has already terminated.
220
221			If the thread being C<join>ed C<die>d, the error it died with will
222			be returned at this time. If you don't want the thread performing
223			the C<join> to die as well, you should either wrap the C<join> in
224			an C<eval> or use the C<eval> thread method instead of C<join>.
225
226			=item eval
227
228			The C<eval> method wraps an C<eval> around a C<join>, and so waits for
229			a thread to exit, passing along any values the thread might have returned.
230			Errors, of course, get placed into C<$@>. (Not available with ithreads.)
231
232			=item detach
233
234			C<detach> tells a thread that it is never going to be joined i.e.
235			that all traces of its existence can be removed once it stops running.
236			Errors in detached threads will not be visible anywhere - if you want
237			to catch them, you should use $SIG{__DIE__} or something like that.
238
239			=item equal
240
241			C<equal> tests whether two thread objects represent the same thread and
242			returns true if they do.
243
244			=item tid
245
246			The C<tid> method returns the tid of a thread. The tid is
247			a monotonically increasing integer assigned when a thread is
248			created. The main thread of a program will have a tid of zero,
249			while subsequent threads will have tids assigned starting with one.
250
251			=item flags
252
253			The C<flags> method returns the flags for the thread. This is the
254			integer value corresponding to the internal flags for the thread,
255			and the value may not be all that meaningful to you.
256			(Not available with ithreads.)
257
258			=item done
259
260			The C<done> method returns true if the thread you're checking has
261			finished, and false otherwise. (Not available with ithreads.)
262
263			=back
264
265			=head1 LIMITATIONS
266
267			The sequence number used to assign tids is a simple integer, and no
268			checking is done to make sure the tid isn't currently in use. If a
269			program creates more than 2**32 - 1 threads in a single run, threads
270			may be assigned duplicate tids. This limitation may be lifted in
271			a future version of Perl.
272
273			=head1 SEE ALSO
274
275			L<threads::shared> (not available with 5005threads)
276
277			L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>,
278			L<Thread::Specific> (not available with ithreads)
279
280			=cut
281
282			#
283			# Methods
284			#
285
286			#
287			# Exported functions
288			#
289
290			sub async (&) {
291			return Thread->new($_[0]);
292			}
293
294			sub eval {
295			return eval { shift->join; };
296			}
297
298			sub unimplemented {
299			print $_[0], " unimplemented with ",
300			$Config{useithreads} ? "ithreads" : "5005threads", "\n";
301
302			}
303
304			sub unimplement {
305			for my $m (@_) {
306			no strict 'refs';
307			*{"Thread::$m"} = sub { unimplemented $m };
308			}
309			}
310
311			BEGIN {
312			if ($ithreads) {
313			if ($othreads) {
314			require Carp;
315			Carp::croak("This Perl has both ithreads and 5005threads (serious malconfiguration)");
316			}
317			XSLoader::load 'threads';
318			for my $m (qw(new join detach yield self tid equal list)) {
319			no strict 'refs';
320			*{"Thread::$m"} = \&{"threads::$m"};
321			}
322			require 'threads/shared.pm';
323			for my $m (qw(cond_signal cond_broadcast cond_wait)) {
324			no strict 'refs';
325			*{"Thread::$m"} = \&{"threads::shared::${m}_enabled"};
326			}
327			# trying to unimplement eval gives redefined warning
328			unimplement(qw(done flags));
329			} elsif ($othreads) {
330			XSLoader::load 'Thread';
331			} else {
332			require Carp;
333			Carp::croak("This Perl has neither ithreads nor 5005threads");
334			}
335			}
336
337			1;