1 package threads::shared;
8 our @ISA = qw(Exporter);
9 our @EXPORT = qw(share cond_wait cond_broadcast cond_signal);
10 our $VERSION = '0.91';
12 if ($threads::threads) {
13 *cond_wait = \&cond_wait_enabled;
14 *cond_signal = \&cond_signal_enabled;
15 *cond_broadcast = \&cond_broadcast_enabled;
17 XSLoader::load('threads::shared',$VERSION);
22 # String eval is generally evil, but we don't want these subs to exist at all
23 # if threads are loaded successfully. Vivifying them conditionally this way
24 # saves on average about 4K of memory per thread.
27 sub cond_wait (\[$@%]) { undef }
28 sub cond_signal (\[$@%]) { undef }
29 sub cond_broadcast (\[$@%]) { undef }
30 sub share (\[$@%]) { return $_[0] }
35 $threads::shared::threads_shared = 1;
37 sub threads::shared::tie::SPLICE
39 die "Splice not implemented for shared arrays";
46 threads::shared - Perl extension for sharing data structures between threads
55 my($scalar, @array, %hash);
60 $hash{bar} = &share({});
65 cond_broadcast(@array);
70 By default, variables are private to each thread, and each newly created
71 thread gets a private copy of each existing variable. This module allows
72 you to share variables across different threads (and pseudoforks on Win32).
73 It is used together with the threads module.
77 C<share>, C<cond_wait>, C<cond_signal>, C<cond_broadcast>
79 Note that if this module is imported when C<threads> has not yet been
80 loaded, then these functions all become no-ops. This makes it possible
81 to write modules that will work in both threaded and non-threaded
90 C<share> takes a value and marks it as shared. You can share a scalar,
91 array, hash, scalar ref, array ref or hash ref. C<share> will return
92 the shared rvalue but always as a reference.
94 C<share> will traverse up references exactly I<one> level.
95 C<share(\$a)> is equivalent to C<share($a)>, while C<share(\\$a)> is not.
97 A variable can also be marked as shared at compile time by using the
98 C<shared> attribute: C<my $var : shared>.
100 If you want to share a newly created reference unfortunately you
101 need to use C<&share([])> and C<&share({})> syntax due to problems
102 with Perl's prototyping.
106 C<lock> places a lock on a variable until the lock goes out of scope.
107 If the variable is locked by another thread, the C<lock> call will
108 block until it's available. C<lock> is recursive, so multiple calls
109 to C<lock> are safe -- the variable will remain locked until the
110 outermost lock on the variable goes out of scope.
112 If a container object, such as a hash or array, is locked, all the
113 elements of that container are not locked. For example, if a thread
114 does a C<lock @a>, any other thread doing a C<lock($a[12])> won't block.
116 C<lock> will traverse up references exactly I<one> level.
117 C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
119 Note that you cannot explicitly unlock a variable; you can only wait
120 for the lock to go out of scope. If you need more fine-grained
121 control, see L<Thread::Semaphore>.
123 =item cond_wait VARIABLE
125 The C<cond_wait> function takes a B<locked> variable as a parameter,
126 unlocks the variable, and blocks until another thread does a
127 C<cond_signal> or C<cond_broadcast> for that same locked variable.
128 The variable that C<cond_wait> blocked on is relocked after the
129 C<cond_wait> is satisfied. If there are multiple threads
130 C<cond_wait>ing on the same variable, all but one will reblock waiting
131 to reacquire the lock on the variable. (So if you're only using
132 C<cond_wait> for synchronisation, give up the lock as soon as
133 possible). The two actions of unlocking the variable and entering the
134 blocked wait state are atomic, The two actions of exiting from the
135 blocked wait state and relocking the variable are not.
137 It is important to note that the variable can be notified even if
138 no thread C<cond_signal> or C<cond_broadcast> on the variable.
139 It is therefore important to check the value of the variable and
140 go back to waiting if the requirement is not fulfilled.
142 =item cond_signal VARIABLE
144 The C<cond_signal> function takes a B<locked> variable as a parameter
145 and unblocks one thread that's C<cond_wait>ing on that variable. If
146 more than one thread is blocked in a C<cond_wait> on that variable,
147 only one (and which one is indeterminate) will be unblocked.
149 If there are no threads blocked in a C<cond_wait> on the variable,
150 the signal is discarded. By always locking before signaling, you can
151 (with care), avoid signaling before another thread has entered cond_wait().
153 C<cond_signal> will normally generate a warning if you attempt to use it
154 on an unlocked variable. On the rare occasions where doing this may be
155 sensible, you can skip the warning with
157 { no warnings 'threads'; cond_signal($foo) }
159 =item cond_broadcast VARIABLE
161 The C<cond_broadcast> function works similarly to C<cond_signal>.
162 C<cond_broadcast>, though, will unblock B<all> the threads that are
163 blocked in a C<cond_wait> on the locked variable, rather than only one.
169 threads::shared is designed to disable itself silently if threads are
170 not available. If you want access to threads, you must C<use threads>
171 before you C<use threads::shared>. threads will emit a warning if you
172 use it after threads::shared.
176 C<bless> is not supported on shared references. In the current version,
177 C<bless> will only bless the thread local reference and the blessing
178 will not propagate to the other threads. This is expected to be
179 implemented in a future version of Perl.
181 Does not support splice on arrays!
183 Taking references to the elements of shared arrays and hashes does not
184 autovivify the elements, and neither does slicing a shared array/hash
185 over non-existent indices/keys autovivify the elements.
187 share() allows you to C<< share $hashref->{key} >> without giving any error
188 message. But the C<< $hashref->{key} >> is B<not> shared, causing the error
189 "locking can only be used on shared values" to occur when you attempt to
190 C<< lock $hasref->{key} >>.
194 Arthur Bergman E<lt>arthur at contiller.seE<gt>
196 threads::shared is released under the same license as Perl
198 Documentation borrowed from the old Thread.pm
202 L<threads>, L<perlthrtut>, L<http://www.perl.com/pub/a/2002/06/11/threads.html>