threads/shared/shared.pm

package threads::shared;

use 5.008;
use strict;
use warnings;
BEGIN {
    require Exporter;
    our @ISA = qw(Exporter);
    our @EXPORT = qw(share cond_wait cond_timedwait cond_broadcast cond_signal);
    our $VERSION = '0.93';

    if ($threads::threads) {
        *cond_wait = \&cond_wait_enabled;
        *cond_timedwait = \&cond_timedwait_enabled;
        *cond_signal = \&cond_signal_enabled;
        *cond_broadcast = \&cond_broadcast_enabled;
        require XSLoader;
        XSLoader::load('threads::shared',$VERSION);
        push @EXPORT,'bless';
    }
    else {

# String eval is generally evil, but we don't want these subs to exist at all
# if threads are loaded successfully.  Vivifying them conditionally this way
# saves on average about 4K of memory per thread.

        eval <<'EOD';
sub cond_wait      (\[$@%];\[$@%])  { undef }
sub cond_timedwait (\[$@%]$;\[$@%]) { undef }
sub cond_signal    (\[$@%])         { undef }
sub cond_broadcast (\[$@%])         { undef }
sub share          (\[$@%])         { return $_[0] }
EOD
    }
}

$threads::shared::threads_shared = 1;

sub threads::shared::tie::SPLICE
{
 die "Splice not implemented for shared arrays";
}

__END__

=head1 NAME

threads::shared - Perl extension for sharing data structures between threads

=head1 SYNOPSIS

  use threads;
  use threads::shared;

  my $var : shared;

  my($scalar, @array, %hash);
  share($scalar);
  share(@array);
  share(%hash);
  my $bar = &share([]);
  $hash{bar} = &share({});

  { lock(%hash); ...  }

  cond_wait($scalar);
  cond_timedwait($scalar, time() + 30);
  cond_broadcast(@array);
  cond_signal(%hash);

  my $lockvar : shared;
  # condition var != lock var
  cond_wait($var, $lockvar);
  cond_timedwait($var, time()+30, $lockvar);

=head1 DESCRIPTION

By default, variables are private to each thread, and each newly created
thread gets a private copy of each existing variable.  This module allows
you to share variables across different threads (and pseudoforks on Win32).
It is used together with the threads module.

=head1 EXPORT

C<share>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>, C<cond_broadcast>

Note that if this module is imported when C<threads> has not yet been
loaded, then these functions all become no-ops. This makes it possible
to write modules that will work in both threaded and non-threaded
environments.

=head1 FUNCTIONS

=over 4

=item share VARIABLE

C<share> takes a value and marks it as shared. You can share a scalar,
array, hash, scalar ref, array ref or hash ref.  C<share> will return
the shared rvalue but always as a reference.

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

A variable can also be marked as shared at compile time by using the
C<shared> attribute: C<my $var : shared>.

If you want to share a newly created reference unfortunately you
need to use C<&share([])> and C<&share({})> syntax due to problems
with Perl's prototyping.

=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.

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.

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.

Note that you cannot explicitly unlock a variable; you can only wait
for the lock to go out of scope. If you need more fine-grained
control, see L<Thread::Semaphore>.

=item cond_wait VARIABLE

=item cond_wait CONDVAR, LOCKVAR

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 reacquire the lock on the variable. (So if you're only using
C<cond_wait> for synchronisation, give up the lock as soon as
possible). The two actions of unlocking the variable and entering the
blocked wait state are atomic, the two actions of exiting from the
blocked wait state and relocking the variable are not.

In its second form, C<cond_wait> takes a shared, B<unlocked> variable
followed by a shared, B<locked> variable.  The second variable is
unlocked and thread execution suspended until another thread signals
the first variable.

It is important to note that the variable can be notified even if
no thread C<cond_signal> or C<cond_broadcast> on the variable.
It is therefore important to check the value of the variable and
go back to waiting if the requirement is not fulfilled.  For example,
to pause until a shared counter drops to zero:

    { lock($counter); cond_wait($count) until $counter == 0; }

=item cond_timedwait VARIABLE, ABS_TIMEOUT

=item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR

In its two-argument form, C<cond_timedwait> takes a B<locked> variable
and an absolute timeout as parameters, unlocks the variable, and blocks
until the timeout is reached or another thread signals the variable.  A
false value is returned if the timeout is reached, and a true value
otherwise.  In either case, the variable is re-locked upon return.

Like C<cond_wait>, this function may take a shared, B<locked> variable
as an additional parameter; in this case the first parameter is an
B<unlocked> condition variable protected by a distinct lock variable.

Again like C<cond_wait>, waking up and reacquiring the lock are not
atomic, and you should always check your desired condition after this
function returns.  Since the timeout is an absolute value, however, it
does not have to be recalculated with each pass:

    lock($var);
    my $abs = time() + 15;
    until ($ok = desired_condition($var)) {
      last if !cond_timedwait($var, $abs);
    }
    # we got it if $ok, otherwise we timed out!

=item cond_signal VARIABLE

The C<cond_signal> function takes a B<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. By always locking before signaling, you can
(with care), avoid signaling before another thread has entered cond_wait().

C<cond_signal> will normally generate a warning if you attempt to use it
on an unlocked variable. On the rare occasions where doing this may be
sensible, you can skip the warning with

    { no warnings 'threads'; cond_signal($foo) }

=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.

=back

=head1 NOTES

threads::shared is designed to disable itself silently if threads are
not available. If you want access to threads, you must C<use threads>
before you C<use threads::shared>.  threads will emit a warning if you
use it after threads::shared.

=head1 BUGS

C<bless> is not supported on shared references. In the current version,
C<bless> will only bless the thread local reference and the blessing
will not propagate to the other threads. This is expected to be
implemented in a future version of Perl.

Does not support splice on arrays!

Taking references to the elements of shared arrays and hashes does not
autovivify the elements, and neither does slicing a shared array/hash
over non-existent indices/keys autovivify the elements.

share() allows you to C<< share $hashref->{key} >> without giving any error
message.  But the C<< $hashref->{key} >> is B<not> shared, causing the error
"locking can only be used on shared values" to occur when you attempt to
C<< lock $hasref->{key} >>.

=head1 AUTHOR

Arthur Bergman E<lt>arthur at contiller.seE<gt>

threads::shared is released under the same license as Perl

Documentation borrowed from the old Thread.pm

=head1 SEE ALSO

L<threads>, L<perlthrtut>, L<http://www.perl.com/pub/a/2002/06/11/threads.html>

=cut
Revision:	1.1
Committed:	Thu Jun 30 14:27:06 2005 UTC (21 years, 4 months ago) by root
Branch:	MAIN
CVS Tags:	PERL-5-8-7, HEAD
Branch point for:	PERL
Log Message:	* empty log message *
#	Content
1	package threads::shared;
2
3	use 5.008;
4	use strict;
5	use warnings;
6	BEGIN {
7	require Exporter;
8	our @ISA = qw(Exporter);
9	our @EXPORT = qw(share cond_wait cond_timedwait cond_broadcast cond_signal);
10	our $VERSION = '0.93';
11
12	if ($threads::threads) {
13	*cond_wait = \&cond_wait_enabled;
14	*cond_timedwait = \&cond_timedwait_enabled;
15	*cond_signal = \&cond_signal_enabled;
16	*cond_broadcast = \&cond_broadcast_enabled;
17	require XSLoader;
18	XSLoader::load('threads::shared',$VERSION);
19	push @EXPORT,'bless';
20	}
21	else {
22
23	# String eval is generally evil, but we don't want these subs to exist at all
24	# if threads are loaded successfully. Vivifying them conditionally this way
25	# saves on average about 4K of memory per thread.
26
27	eval <<'EOD';
28	sub cond_wait (\[$@%];\[$@%]) { undef }
29	sub cond_timedwait (\[$@%]$;\[$@%]) { undef }
30	sub cond_signal (\[$@%]) { undef }
31	sub cond_broadcast (\[$@%]) { undef }
32	sub share (\[$@%]) { return $_[0] }
33	EOD
34	}
35	}
36
37	$threads::shared::threads_shared = 1;
38
39	sub threads::shared::tie::SPLICE
40	{
41	die "Splice not implemented for shared arrays";
42	}
43
44	__END__
45
46	=head1 NAME
47
48	threads::shared - Perl extension for sharing data structures between threads
49
50	=head1 SYNOPSIS
51
52	use threads;
53	use threads::shared;
54
55	my $var : shared;
56
57	my($scalar, @array, %hash);
58	share($scalar);
59	share(@array);
60	share(%hash);
61	my $bar = &share([]);
62	$hash{bar} = &share({});
63
64	{ lock(%hash); ... }
65
66	cond_wait($scalar);
67	cond_timedwait($scalar, time() + 30);
68	cond_broadcast(@array);
69	cond_signal(%hash);
70
71	my $lockvar : shared;
72	# condition var != lock var
73	cond_wait($var, $lockvar);
74	cond_timedwait($var, time()+30, $lockvar);
75
76	=head1 DESCRIPTION
77
78	By default, variables are private to each thread, and each newly created
79	thread gets a private copy of each existing variable. This module allows
80	you to share variables across different threads (and pseudoforks on Win32).
81	It is used together with the threads module.
82
83	=head1 EXPORT
84
85	C<share>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>, C<cond_broadcast>
86
87	Note that if this module is imported when C<threads> has not yet been
88	loaded, then these functions all become no-ops. This makes it possible
89	to write modules that will work in both threaded and non-threaded
90	environments.
91
92	=head1 FUNCTIONS
93
94	=over 4
95
96	=item share VARIABLE
97
98	C<share> takes a value and marks it as shared. You can share a scalar,
99	array, hash, scalar ref, array ref or hash ref. C<share> will return
100	the shared rvalue but always as a reference.
101
102	C<share> will traverse up references exactly I<one> level.
103	C<share(\$a)> is equivalent to C<share($a)>, while C<share(\\$a)> is not.
104
105	A variable can also be marked as shared at compile time by using the
106	C<shared> attribute: C<my $var : shared>.
107
108	If you want to share a newly created reference unfortunately you
109	need to use C<&share([])> and C<&share({})> syntax due to problems
110	with Perl's prototyping.
111
112	=item lock VARIABLE
113
114	C<lock> places a lock on a variable until the lock goes out of scope.
115	If the variable is locked by another thread, the C<lock> call will
116	block until it's available. C<lock> is recursive, so multiple calls
117	to C<lock> are safe -- the variable will remain locked until the
118	outermost lock on the variable goes out of scope.
119
120	If a container object, such as a hash or array, is locked, all the
121	elements of that container are not locked. For example, if a thread
122	does a C<lock @a>, any other thread doing a C<lock($a[12])> won't block.
123
124	C<lock> will traverse up references exactly I<one> level.
125	C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
126
127	Note that you cannot explicitly unlock a variable; you can only wait
128	for the lock to go out of scope. If you need more fine-grained
129	control, see L<Thread::Semaphore>.
130
131	=item cond_wait VARIABLE
132
133	=item cond_wait CONDVAR, LOCKVAR
134
135	The C<cond_wait> function takes a B<locked> variable as a parameter,
136	unlocks the variable, and blocks until another thread does a
137	C<cond_signal> or C<cond_broadcast> for that same locked variable.
138	The variable that C<cond_wait> blocked on is relocked after the
139	C<cond_wait> is satisfied. If there are multiple threads
140	C<cond_wait>ing on the same variable, all but one will reblock waiting
141	to reacquire the lock on the variable. (So if you're only using
142	C<cond_wait> for synchronisation, give up the lock as soon as
143	possible). The two actions of unlocking the variable and entering the
144	blocked wait state are atomic, the two actions of exiting from the
145	blocked wait state and relocking the variable are not.
146
147	In its second form, C<cond_wait> takes a shared, B<unlocked> variable
148	followed by a shared, B<locked> variable. The second variable is
149	unlocked and thread execution suspended until another thread signals
150	the first variable.
151
152	It is important to note that the variable can be notified even if
153	no thread C<cond_signal> or C<cond_broadcast> on the variable.
154	It is therefore important to check the value of the variable and
155	go back to waiting if the requirement is not fulfilled. For example,
156	to pause until a shared counter drops to zero:
157
158	{ lock($counter); cond_wait($count) until $counter == 0; }
159
160	=item cond_timedwait VARIABLE, ABS_TIMEOUT
161
162	=item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR
163
164	In its two-argument form, C<cond_timedwait> takes a B<locked> variable
165	and an absolute timeout as parameters, unlocks the variable, and blocks
166	until the timeout is reached or another thread signals the variable. A
167	false value is returned if the timeout is reached, and a true value
168	otherwise. In either case, the variable is re-locked upon return.
169
170	Like C<cond_wait>, this function may take a shared, B<locked> variable
171	as an additional parameter; in this case the first parameter is an
172	B<unlocked> condition variable protected by a distinct lock variable.
173
174	Again like C<cond_wait>, waking up and reacquiring the lock are not
175	atomic, and you should always check your desired condition after this
176	function returns. Since the timeout is an absolute value, however, it
177	does not have to be recalculated with each pass:
178
179	lock($var);
180	my $abs = time() + 15;
181	until ($ok = desired_condition($var)) {
182	last if !cond_timedwait($var, $abs);
183	}
184	# we got it if $ok, otherwise we timed out!
185
186	=item cond_signal VARIABLE
187
188	The C<cond_signal> function takes a B<locked> variable as a parameter
189	and unblocks one thread that's C<cond_wait>ing on that variable. If
190	more than one thread is blocked in a C<cond_wait> on that variable,
191	only one (and which one is indeterminate) will be unblocked.
192
193	If there are no threads blocked in a C<cond_wait> on the variable,
194	the signal is discarded. By always locking before signaling, you can
195	(with care), avoid signaling before another thread has entered cond_wait().
196
197	C<cond_signal> will normally generate a warning if you attempt to use it
198	on an unlocked variable. On the rare occasions where doing this may be
199	sensible, you can skip the warning with
200
201	{ no warnings 'threads'; cond_signal($foo) }
202
203	=item cond_broadcast VARIABLE
204
205	The C<cond_broadcast> function works similarly to C<cond_signal>.
206	C<cond_broadcast>, though, will unblock B<all> the threads that are
207	blocked in a C<cond_wait> on the locked variable, rather than only one.
208
209	=back
210
211	=head1 NOTES
212
213	threads::shared is designed to disable itself silently if threads are
214	not available. If you want access to threads, you must C<use threads>
215	before you C<use threads::shared>. threads will emit a warning if you
216	use it after threads::shared.
217
218	=head1 BUGS
219
220	C<bless> is not supported on shared references. In the current version,
221	C<bless> will only bless the thread local reference and the blessing
222	will not propagate to the other threads. This is expected to be
223	implemented in a future version of Perl.
224
225	Does not support splice on arrays!
226
227	Taking references to the elements of shared arrays and hashes does not
228	autovivify the elements, and neither does slicing a shared array/hash
229	over non-existent indices/keys autovivify the elements.
230
231	share() allows you to C<< share $hashref->{key} >> without giving any error
232	message. But the C<< $hashref->{key} >> is B<not> shared, causing the error
233	"locking can only be used on shared values" to occur when you attempt to
234	C<< lock $hasref->{key} >>.
235
236	=head1 AUTHOR
237
238	Arthur Bergman E<lt>arthur at contiller.seE<gt>
239
240	threads::shared is released under the same license as Perl
241
242	Documentation borrowed from the old Thread.pm
243
244	=head1 SEE ALSO
245
246	L<threads>, L<perlthrtut>, L<http://www.perl.com/pub/a/2002/06/11/threads.html>
247
248	=cut