1 package threads::shared;
8 our @ISA = qw(Exporter);
9 our @EXPORT = qw(share cond_wait cond_timedwait cond_broadcast cond_signal);
10 our $VERSION = '0.94_01';
12 if ($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 $var = $shared_ref_value;
58 $var = &share($simple_unshared_ref_value);
59 $var = &share(new Foo);
61 my($scalar, @array, %hash);
66 $hash{bar} = &share({});
71 cond_timedwait($scalar, time() + 30);
72 cond_broadcast(@array);
76 # condition var != lock var
77 cond_wait($var, $lockvar);
78 cond_timedwait($var, time()+30, $lockvar);
82 By default, variables are private to each thread, and each newly created
83 thread gets a private copy of each existing variable. This module allows
84 you to share variables across different threads (and pseudoforks on Win32).
85 It is used together with the threads module.
89 C<share>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>, C<cond_broadcast>
91 Note that if this module is imported when C<threads> has not yet been
92 loaded, then these functions all become no-ops. This makes it possible
93 to write modules that will work in both threaded and non-threaded
102 C<share> takes a value and marks it as shared. You can share a scalar,
103 array, hash, scalar ref, array ref or hash ref. C<share> will return
104 the shared rvalue but always as a reference.
106 C<share> will traverse up references exactly I<one> level.
107 C<share(\$a)> is equivalent to C<share($a)>, while C<share(\\$a)> is not.
108 This means that you must create nested shared data structures by first
109 creating individual shared leaf notes, then adding them to a shared hash
112 A variable can also be marked as shared at compile time by using the
113 C<shared> attribute: C<my $var : shared>.
115 If you want to share a newly created reference unfortunately you
116 need to use C<&share([])> and C<&share({})> syntax due to problems
117 with Perl's prototyping.
119 The only values that can be assigned to a shared scalar are other scalar
120 values, or shared refs, eg
124 $var = &share([]); # ok
126 $var = A->new; # error
127 $var = &share(A->new); # ok as long as the A object is not nested
129 Note that it is often not wise to share an object unless the class itself
130 has been written to support sharing; for example, an object's destructor
131 may get called multiple times, one for each thread's scope exit.
135 C<lock> places a lock on a variable until the lock goes out of scope.
136 If the variable is locked by another thread, the C<lock> call will
137 block until it's available. C<lock> is recursive, so multiple calls
138 to C<lock> are safe -- the variable will remain locked until the
139 outermost lock on the variable goes out of scope.
141 If a container object, such as a hash or array, is locked, all the
142 elements of that container are not locked. For example, if a thread
143 does a C<lock @a>, any other thread doing a C<lock($a[12])> won't block.
145 C<lock> will traverse up references exactly I<one> level.
146 C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
148 Note that you cannot explicitly unlock a variable; you can only wait
149 for the lock to go out of scope. If you need more fine-grained
150 control, see L<Thread::Semaphore>.
152 =item cond_wait VARIABLE
154 =item cond_wait CONDVAR, LOCKVAR
156 The C<cond_wait> function takes a B<locked> variable as a parameter,
157 unlocks the variable, and blocks until another thread does a
158 C<cond_signal> or C<cond_broadcast> for that same locked variable.
159 The variable that C<cond_wait> blocked on is relocked after the
160 C<cond_wait> is satisfied. If there are multiple threads
161 C<cond_wait>ing on the same variable, all but one will reblock waiting
162 to reacquire the lock on the variable. (So if you're only using
163 C<cond_wait> for synchronisation, give up the lock as soon as
164 possible). The two actions of unlocking the variable and entering the
165 blocked wait state are atomic, the two actions of exiting from the
166 blocked wait state and relocking the variable are not.
168 In its second form, C<cond_wait> takes a shared, B<unlocked> variable
169 followed by a shared, B<locked> variable. The second variable is
170 unlocked and thread execution suspended until another thread signals
173 It is important to note that the variable can be notified even if
174 no thread C<cond_signal> or C<cond_broadcast> on the variable.
175 It is therefore important to check the value of the variable and
176 go back to waiting if the requirement is not fulfilled. For example,
177 to pause until a shared counter drops to zero:
179 { lock($counter); cond_wait($count) until $counter == 0; }
181 =item cond_timedwait VARIABLE, ABS_TIMEOUT
183 =item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR
185 In its two-argument form, C<cond_timedwait> takes a B<locked> variable
186 and an absolute timeout as parameters, unlocks the variable, and blocks
187 until the timeout is reached or another thread signals the variable. A
188 false value is returned if the timeout is reached, and a true value
189 otherwise. In either case, the variable is re-locked upon return.
191 Like C<cond_wait>, this function may take a shared, B<locked> variable
192 as an additional parameter; in this case the first parameter is an
193 B<unlocked> condition variable protected by a distinct lock variable.
195 Again like C<cond_wait>, waking up and reacquiring the lock are not
196 atomic, and you should always check your desired condition after this
197 function returns. Since the timeout is an absolute value, however, it
198 does not have to be recalculated with each pass:
201 my $abs = time() + 15;
202 until ($ok = desired_condition($var)) {
203 last if !cond_timedwait($var, $abs);
205 # we got it if $ok, otherwise we timed out!
207 =item cond_signal VARIABLE
209 The C<cond_signal> function takes a B<locked> variable as a parameter
210 and unblocks one thread that's C<cond_wait>ing on that variable. If
211 more than one thread is blocked in a C<cond_wait> on that variable,
212 only one (and which one is indeterminate) will be unblocked.
214 If there are no threads blocked in a C<cond_wait> on the variable,
215 the signal is discarded. By always locking before signaling, you can
216 (with care), avoid signaling before another thread has entered cond_wait().
218 C<cond_signal> will normally generate a warning if you attempt to use it
219 on an unlocked variable. On the rare occasions where doing this may be
220 sensible, you can skip the warning with
222 { no warnings 'threads'; cond_signal($foo) }
224 =item cond_broadcast VARIABLE
226 The C<cond_broadcast> function works similarly to C<cond_signal>.
227 C<cond_broadcast>, though, will unblock B<all> the threads that are
228 blocked in a C<cond_wait> on the locked variable, rather than only one.
234 threads::shared is designed to disable itself silently if threads are
235 not available. If you want access to threads, you must C<use threads>
236 before you C<use threads::shared>. threads will emit a warning if you
237 use it after threads::shared.
241 C<bless> is not supported on shared references. In the current version,
242 C<bless> will only bless the thread local reference and the blessing
243 will not propagate to the other threads. This is expected to be
244 implemented in a future version of Perl.
246 Does not support splice on arrays!
248 Taking references to the elements of shared arrays and hashes does not
249 autovivify the elements, and neither does slicing a shared array/hash
250 over non-existent indices/keys autovivify the elements.
252 share() allows you to C<< share $hashref->{key} >> without giving any error
253 message. But the C<< $hashref->{key} >> is B<not> shared, causing the error
254 "locking can only be used on shared values" to occur when you attempt to
255 C<< lock $hasref->{key} >>.
259 Arthur Bergman E<lt>arthur at contiller.seE<gt>
261 threads::shared is released under the same license as Perl
263 Documentation borrowed from the old Thread.pm
267 L<threads>, L<perlthrtut>, L<http://www.perl.com/pub/a/2002/06/11/threads.html>