1 package threads::shared;
8 our @ISA = qw(Exporter);
9 our @EXPORT = qw(share cond_wait cond_timedwait cond_broadcast cond_signal);
10 our $VERSION = '0.92';
12 if ($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;
18 XSLoader::load('threads::shared',$VERSION);
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.
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] }
37 $threads::shared::threads_shared = 1;
39 sub threads::shared::tie::SPLICE
41 die "Splice not implemented for shared arrays";
48 threads::shared - Perl extension for sharing data structures between threads
57 my($scalar, @array, %hash);
62 $hash{bar} = &share({});
67 cond_timedwait($scalar, time() + 30);
68 cond_broadcast(@array);
72 # condition var != lock var
73 cond_wait($var, $lockvar);
74 cond_timedwait($var, time()+30, $lockvar);
78 By default, variables are private to each thread, and each newly created
79 thread gets a private copy of each existing variable. This module allows
80 you to share variables across different threads (and pseudoforks on Win32).
81 It is used together with the threads module.
85 C<share>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>, C<cond_broadcast>
87 Note that if this module is imported when C<threads> has not yet been
88 loaded, then these functions all become no-ops. This makes it possible
89 to write modules that will work in both threaded and non-threaded
98 C<share> takes a value and marks it as shared. You can share a scalar,
99 array, hash, scalar ref, array ref or hash ref. C<share> will return
100 the shared rvalue but always as a reference.
102 C<share> will traverse up references exactly I<one> level.
103 C<share(\$a)> is equivalent to C<share($a)>, while C<share(\\$a)> is not.
105 A variable can also be marked as shared at compile time by using the
106 C<shared> attribute: C<my $var : shared>.
108 If you want to share a newly created reference unfortunately you
109 need to use C<&share([])> and C<&share({})> syntax due to problems
110 with Perl's prototyping.
114 C<lock> places a lock on a variable until the lock goes out of scope.
115 If the variable is locked by another thread, the C<lock> call will
116 block until it's available. C<lock> is recursive, so multiple calls
117 to C<lock> are safe -- the variable will remain locked until the
118 outermost lock on the variable goes out of scope.
120 If a container object, such as a hash or array, is locked, all the
121 elements of that container are not locked. For example, if a thread
122 does a C<lock @a>, any other thread doing a C<lock($a[12])> won't block.
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.
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>.
131 =item cond_wait VARIABLE
133 =item cond_wait CONDVAR, LOCKVAR
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.
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
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:
158 { lock($counter); cond_wait($count) until $counter == 0; }
160 =item cond_timedwait VARIABLE, ABS_TIMEOUT
162 =item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR
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.
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.
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:
180 my $abs = time() + 15;
181 until ($ok = desired_condition($var)) {
182 last if !cond_timedwait($var, $abs);
184 # we got it if $ok, otherwise we timed out!
186 =item cond_signal VARIABLE
188 The C<cond_signal> function takes a B<locked> variable as a parameter
189 and unblocks one thread that's C<cond_wait>ing on that variable. If
190 more than one thread is blocked in a C<cond_wait> on that variable,
191 only one (and which one is indeterminate) will be unblocked.
193 If there are no threads blocked in a C<cond_wait> on the variable,
194 the signal is discarded. By always locking before signaling, you can
195 (with care), avoid signaling before another thread has entered cond_wait().
197 C<cond_signal> will normally generate a warning if you attempt to use it
198 on an unlocked variable. On the rare occasions where doing this may be
199 sensible, you can skip the warning with
201 { no warnings 'threads'; cond_signal($foo) }
203 =item cond_broadcast VARIABLE
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.
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.
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.
225 Does not support splice on arrays!
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.
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} >>.
238 Arthur Bergman E<lt>arthur at contiller.seE<gt>
240 threads::shared is released under the same license as Perl
242 Documentation borrowed from the old Thread.pm
246 L<threads>, L<perlthrtut>, L<http://www.perl.com/pub/a/2002/06/11/threads.html>