1 package threads::shared;
8 use Scalar::Util qw(reftype refaddr blessed);
10 our $VERSION = '1.47'; # Please update the pod, too.
11 my $XS_VERSION = $VERSION;
12 $VERSION = eval $VERSION;
14 # Declare that we have been loaded
15 $threads::shared::threads_shared = 1;
17 # Method of complaint about things we can't clone
18 $threads::shared::clone_warn = undef;
20 # Load the XS code, if applicable
21 if ($threads::threads) {
23 XSLoader::load('threads::shared', $XS_VERSION);
28 # String eval is generally evil, but we don't want these subs to
29 # exist at all if 'threads' is not loaded successfully.
30 # Vivifying them conditionally this way saves on average about 4K
31 # of memory per thread.
33 sub share (\[$@%]) { return $_[0] }
34 sub is_shared (\[$@%]) { undef }
35 sub cond_wait (\[$@%];\[$@%]) { undef }
36 sub cond_timedwait (\[$@%]$;\[$@%]) { undef }
37 sub cond_signal (\[$@%]) { undef }
38 sub cond_broadcast (\[$@%]) { undef }
47 # Exported subroutines
48 my @EXPORT = qw(share is_shared cond_wait cond_timedwait
49 cond_signal cond_broadcast shared_clone);
50 if ($threads::threads) {
51 push(@EXPORT, 'bless');
54 # Export subroutine names
55 my $caller = caller();
56 foreach my $sym (@EXPORT) {
58 *{$caller.'::'.$sym} = \&{$sym};
63 # Predeclarations for internal functions
69 sub threads::shared::tie::SPLICE
72 Carp::croak('Splice not implemented for shared arrays');
76 # Create a thread-shared clone of a complex data structure or object
81 Carp::croak('Usage: shared_clone(REF)');
84 return $make_shared->(shift, {});
88 ### Internal Functions ###
90 # Used by shared_clone() to recursively clone
91 # a complex data structure or object
93 my ($item, $cloned) = @_;
95 # Just return the item if:
97 # 2. Already shared; or
98 # 3. Not running 'threads'.
99 return $item if (! ref($item) || is_shared($item) || ! $threads::threads);
101 # Check for previously cloned references
102 # (this takes care of circular refs as well)
103 my $addr = refaddr($item);
104 if (exists($cloned->{$addr})) {
105 # Return the already existing clone
106 return $cloned->{$addr};
109 # Make copies of array, hash and scalar refs and refs of refs
111 my $ref_type = reftype($item);
114 if ($ref_type eq 'ARRAY') {
115 # Make empty shared array ref
117 # Add to clone checking hash
118 $cloned->{$addr} = $copy;
119 # Recursively copy and add contents
120 push(@$copy, map { $make_shared->($_, $cloned) } @$item);
124 elsif ($ref_type eq 'HASH') {
125 # Make empty shared hash ref
127 # Add to clone checking hash
128 $cloned->{$addr} = $copy;
129 # Recursively copy and add contents
130 foreach my $key (keys(%{$item})) {
131 $copy->{$key} = $make_shared->($item->{$key}, $cloned);
136 elsif ($ref_type eq 'SCALAR') {
137 $copy = \do{ my $scalar = $$item; };
139 # Add to clone checking hash
140 $cloned->{$addr} = $copy;
143 # Copy of a ref of a ref
144 elsif ($ref_type eq 'REF') {
145 # Special handling for $x = \$x
146 if ($addr == refaddr($$item)) {
149 $cloned->{$addr} = $copy;
154 # Add to clone checking hash
155 $cloned->{$addr} = $copy;
156 # Recursively copy and add contents
157 $tmp = $make_shared->($$item, $cloned);
162 if (! defined($threads::shared::clone_warn)) {
163 Carp::croak("Unsupported ref type: ", $ref_type);
164 } elsif ($threads::shared::clone_warn) {
165 Carp::carp("Unsupported ref type: ", $ref_type);
170 # If input item is an object, then bless the copy into the same class
171 if (my $class = blessed($item)) {
172 bless($copy, $class);
175 # Clone READONLY flag
176 if ($ref_type eq 'SCALAR') {
177 if (Internals::SvREADONLY($$item)) {
178 Internals::SvREADONLY($$copy, 1) if ($] >= 5.008003);
181 if (Internals::SvREADONLY($item)) {
182 Internals::SvREADONLY($copy, 1) if ($] >= 5.008003);
194 threads::shared - Perl extension for sharing data structures between threads
198 This document describes threads::shared version 1.47
209 my ($scalar, @array, %hash);
214 $var = $scalar_value;
215 $var = $shared_ref_value;
216 $var = shared_clone($non_shared_ref_value);
217 $var = shared_clone({'foo' => [qw/foo bar baz/]});
219 $hsh{'foo'} = $scalar_value;
220 $hsh{'bar'} = $shared_ref_value;
221 $hsh{'baz'} = shared_clone($non_shared_ref_value);
222 $hsh{'quz'} = shared_clone([1..3]);
224 $ary[0] = $scalar_value;
225 $ary[1] = $shared_ref_value;
226 $ary[2] = shared_clone($non_shared_ref_value);
227 $ary[3] = shared_clone([ {}, [] ]);
232 cond_timedwait($scalar, time() + 30);
233 cond_broadcast(@array);
237 # condition var != lock var
238 cond_wait($var, $lockvar);
239 cond_timedwait($var, time()+30, $lockvar);
243 By default, variables are private to each thread, and each newly created
244 thread gets a private copy of each existing variable. This module allows you
245 to share variables across different threads (and pseudo-forks on Win32). It
246 is used together with the L<threads> module.
248 This module supports the sharing of the following data types only: scalars
249 and scalar refs, arrays and array refs, and hashes and hash refs.
253 The following functions are exported by this module: C<share>,
254 C<shared_clone>, C<is_shared>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>
255 and C<cond_broadcast>
257 Note that if this module is imported when L<threads> has not yet been loaded,
258 then these functions all become no-ops. This makes it possible to write
259 modules that will work in both threaded and non-threaded environments.
267 C<share> takes a variable and marks it as shared:
269 my ($scalar, @array, %hash);
274 C<share> will return the shared rvalue, but always as a reference.
276 Variables can also be marked as shared at compile time by using the
277 C<:shared> attribute:
279 my ($var, %hash, @array) :shared;
281 Shared variables can only store scalars, refs of shared variables, or
282 refs of shared data (discussed in next section):
284 my ($var, %hash, @array) :shared;
289 $hash{'foo'} = 'bar';
292 # Storing shared refs
294 $hash{'ary'} = \@array;
297 # The following are errors:
298 # $var = \$bork; # ref of non-shared variable
299 # $hash{'bork'} = []; # non-shared array ref
300 # push(@array, { 'x' => 1 }); # non-shared hash ref
302 =item shared_clone REF
304 C<shared_clone> takes a reference, and returns a shared version of its
305 argument, performing a deep copy on any non-shared elements. Any shared
306 elements in the argument are used as is (i.e., they are not cloned).
308 my $cpy = shared_clone({'foo' => [qw/foo bar baz/]});
310 Object status (i.e., the class an object is blessed into) is also cloned.
312 my $obj = {'foo' => [qw/foo bar baz/]};
314 my $cpy = shared_clone($obj);
315 print(ref($cpy), "\n"); # Outputs 'Foo'
317 For cloning empty array or hash refs, the following may also be used:
319 $var = &share([]); # Same as $var = shared_clone([]);
320 $var = &share({}); # Same as $var = shared_clone({});
322 Not all Perl data types can be cloned (e.g., globs, code refs). By default,
323 C<shared_clone> will L<croak|Carp> if it encounters such items. To change
324 this behaviour to a warning, then set the following:
326 $threads::shared::clone_warn = 1;
328 In this case, C<undef> will be substituted for the item to be cloned. If
331 $threads::shared::clone_warn = 0;
333 then the C<undef> substitution will be performed silently.
335 =item is_shared VARIABLE
337 C<is_shared> checks if the specified variable is shared or not. If shared,
338 returns the variable's internal ID (similar to
339 C<refaddr()> (see L<Scalar::Util>). Otherwise, returns C<undef>.
341 if (is_shared($var)) {
342 print("\$var is shared\n");
344 print("\$var is not shared\n");
347 When used on an element of an array or hash, C<is_shared> checks if the
348 specified element belongs to a shared array or hash. (It does not check
349 the contents of that element.)
352 if (is_shared(%hash)) {
353 print("\%hash is shared\n");
357 if (is_shared($hash{'elem'})) {
358 print("\$hash{'elem'} is in a shared hash\n");
363 C<lock> places a B<advisory> lock on a variable until the lock goes out of
364 scope. If the variable is locked by another thread, the C<lock> call will
365 block until it's available. Multiple calls to C<lock> by the same thread from
366 within dynamically nested scopes are safe -- the variable will remain locked
367 until the outermost lock on the variable goes out of scope.
369 C<lock> follows references exactly I<one> level:
373 lock($ref); # This is equivalent to lock(%hash)
375 Note that you cannot explicitly unlock a variable; you can only wait for the
376 lock to go out of scope. This is most easily accomplished by locking the
377 variable inside a block.
382 # $var is locked from here to the end of the block
385 # $var is now unlocked
387 As locks are advisory, they do not prevent data access or modification by
388 another thread that does not itself attempt to obtain a lock on the variable.
390 You cannot lock the individual elements of a container variable:
393 $hash{'foo'} = 'bar';
394 #lock($hash{'foo'}); # Error
397 If you need more fine-grained control over shared variable access, see
398 L<Thread::Semaphore>.
400 =item cond_wait VARIABLE
402 =item cond_wait CONDVAR, LOCKVAR
404 The C<cond_wait> function takes a B<locked> variable as a parameter, unlocks
405 the variable, and blocks until another thread does a C<cond_signal> or
406 C<cond_broadcast> for that same locked variable. The variable that
407 C<cond_wait> blocked on is re-locked after the C<cond_wait> is satisfied. If
408 there are multiple threads C<cond_wait>ing on the same variable, all but one
409 will re-block waiting to reacquire the
410 lock on the variable. (So if you're only
411 using C<cond_wait> for synchronization, give up the lock as soon as possible).
412 The two actions of unlocking the variable and entering the blocked wait state
413 are atomic, the two actions of exiting from the blocked wait state and
414 re-locking the variable are not.
416 In its second form, C<cond_wait> takes a shared, B<unlocked> variable followed
417 by a shared, B<locked> variable. The second variable is unlocked and thread
418 execution suspended until another thread signals the first variable.
420 It is important to note that the variable can be notified even if no thread
421 C<cond_signal> or C<cond_broadcast> on the variable. It is therefore
422 important to check the value of the variable and go back to waiting if the
423 requirement is not fulfilled. For example, to pause until a shared counter
426 { lock($counter); cond_wait($counter) until $counter == 0; }
428 =item cond_timedwait VARIABLE, ABS_TIMEOUT
430 =item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR
432 In its two-argument form, C<cond_timedwait> takes a B<locked> variable and an
433 absolute timeout in I<epoch> seconds (see L<time() in perlfunc|perlfunc/time>
434 for more) as parameters, unlocks the variable, and blocks until the
435 timeout is reached or another thread signals the variable. A false value is
436 returned if the timeout is reached, and a true value otherwise. In either
437 case, the variable is re-locked upon return.
439 Like C<cond_wait>, this function may take a shared, B<locked> variable as an
440 additional parameter; in this case the first parameter is an B<unlocked>
441 condition variable protected by a distinct lock variable.
443 Again like C<cond_wait>, waking up and reacquiring the lock are not atomic,
444 and you should always check your desired condition after this function
445 returns. Since the timeout is an absolute value, however, it does not have to
446 be recalculated with each pass:
449 my $abs = time() + 15;
450 until ($ok = desired_condition($var)) {
451 last if !cond_timedwait($var, $abs);
453 # we got it if $ok, otherwise we timed out!
455 =item cond_signal VARIABLE
457 The C<cond_signal> function takes a B<locked> variable as a parameter and
458 unblocks one thread that's C<cond_wait>ing
459 on that variable. If more than one
460 thread is blocked in a C<cond_wait> on that variable, only one (and which one
461 is indeterminate) will be unblocked.
463 If there are no threads blocked in a C<cond_wait> on the variable, the signal
464 is discarded. By always locking before
465 signaling, you can (with care), avoid
466 signaling before another thread has entered cond_wait().
468 C<cond_signal> will normally generate a warning if you attempt to use it on an
469 unlocked variable. On the rare occasions
470 where doing this may be sensible, you
471 can suppress the warning with:
473 { no warnings 'threads'; cond_signal($foo); }
475 =item cond_broadcast VARIABLE
477 The C<cond_broadcast> function works similarly to C<cond_signal>.
478 C<cond_broadcast>, though, will unblock B<all> the threads that are blocked in
479 a C<cond_wait> on the locked variable, rather than only one.
485 L<threads::shared> exports a version of L<bless()|perlfunc/"bless REF"> that
486 works on shared objects such that I<blessings> propagate across threads.
488 # Create a shared 'Foo' object
489 my $foo :shared = shared_clone({});
492 # Create a shared 'Bar' object
493 my $bar :shared = shared_clone({});
496 # Put 'bar' inside 'foo'
497 $foo->{'bar'} = $bar;
499 # Rebless the objects via a thread
500 threads->create(sub {
501 # Rebless the outer object
504 # Cannot directly rebless the inner object
505 #bless($foo->{'bar'}, 'Yang');
507 # Retrieve and rebless the inner object
508 my $obj = $foo->{'bar'};
510 $foo->{'bar'} = $obj;
514 print(ref($foo), "\n"); # Prints 'Yin'
515 print(ref($foo->{'bar'}), "\n"); # Prints 'Yang'
516 print(ref($bar), "\n"); # Also prints 'Yang'
520 L<threads::shared> is designed to disable itself silently if threads are not
521 available. This allows you to write modules and packages that can be used
522 in both threaded and non-threaded applications.
524 If you want access to threads, you must C<use threads> before you
525 C<use threads::shared>. L<threads> will emit a warning if you use it after
532 =item cond_broadcast() called on unlocked variable
534 =item cond_signal() called on unlocked variable
536 See L</"cond_signal VARIABLE">, above.
540 =head1 BUGS AND LIMITATIONS
542 When C<share> is used on arrays, hashes, array refs or hash refs, any data
543 they contain will be lost.
545 my @arr = qw(foo bar baz);
547 # @arr is now empty (i.e., == ());
549 # Create a 'foo' object
550 my $foo = { 'data' => 99 };
554 share($foo); # Contents are now wiped out
555 print("ERROR: \$foo is empty\n")
556 if (! exists($foo->{'data'}));
558 Therefore, populate such variables B<after> declaring them as shared. (Scalar
559 and scalar refs are not affected by this problem.)
561 It is often not wise to share an object unless the class itself has been
562 written to support sharing. For example, an object's destructor may get
563 called multiple times, once for each thread's scope exit. Another danger is
564 that the contents of hash-based objects will be lost due to the above
565 mentioned limitation. See F<examples/class.pl> (in the CPAN distribution of
566 this module) for how to create a class that supports object sharing.
568 Destructors may not be called on objects if those objects still exist at
569 global destruction time. If the destructors must be called, make sure
570 there are no circular references and that nothing is referencing the
571 objects, before the program ends.
573 Does not support C<splice> on arrays. Does not support explicitly changing
574 array lengths via $#array -- use C<push> and C<pop> instead.
576 Taking references to the elements of shared arrays and hashes does not
577 autovivify the elements, and neither does slicing a shared array/hash over
578 non-existent indices/keys autovivify the elements.
580 C<share()> allows you to C<< share($hashref->{key}) >> and
581 C<< share($arrayref->[idx]) >> without giving any error message. But the
582 C<< $hashref->{key} >> or C<< $arrayref->[idx] >> is B<not> shared, causing
583 the error "lock can only be used on shared values" to occur when you attempt
584 to C<< lock($hashref->{key}) >> or C<< lock($arrayref->[idx]) >> in another
587 Using C<refaddr()> is unreliable for testing
588 whether or not two shared references are equivalent (e.g., when testing for
589 circular references). Use L<is_shared()|/"is_shared VARIABLE">, instead:
593 use Scalar::Util qw(refaddr);
595 # If ref is shared, use threads::shared's internal ID.
596 # Otherwise, use refaddr().
597 my $addr1 = is_shared($ref1) || refaddr($ref1);
598 my $addr2 = is_shared($ref2) || refaddr($ref2);
600 if ($addr1 == $addr2) {
601 # The refs are equivalent
604 L<each()|perlfunc/"each HASH"> does not work properly on shared references
605 embedded in shared structures. For example:
608 $foo{'bar'} = shared_clone({'a'=>'x', 'b'=>'y', 'c'=>'z'});
610 while (my ($key, $val) = each(%{$foo{'bar'}})) {
614 Either of the following will work instead:
616 my $ref = $foo{'bar'};
617 while (my ($key, $val) = each(%{$ref})) {
621 foreach my $key (keys(%{$foo{'bar'}})) {
622 my $val = $foo{'bar'}{$key};
626 This module supports dual-valued variables created using C<dualvar()> from
627 L<Scalar::Util>. However, while C<$!> acts
628 like a dualvar, it is implemented as a tied SV. To propagate its value, use
629 the follow construct, if needed:
631 my $errno :shared = dualvar($!,$!);
633 View existing bug reports at, and submit any new bugs, problems, patches, etc.
634 to: L<http://rt.cpan.org/Public/Dist/Display.html?Name=threads-shared>
638 L<threads::shared> Discussion Forum on CPAN:
639 L<http://www.cpanforum.com/dist/threads-shared>
641 L<threads>, L<perlthrtut>
643 L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
644 L<http://www.perl.com/pub/a/2002/09/04/threads.html>
646 Perl threads mailing list:
647 L<http://lists.perl.org/list/ithreads.html>
651 Artur Bergman E<lt>sky AT crucially DOT netE<gt>
653 Documentation borrowed from the old Thread.pm.
655 CPAN version produced by Jerry D. Hedden E<lt>jdhedden AT cpan DOT orgE<gt>.
659 threads::shared is released under the same license as Perl.