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b050c948 1package threads::shared;
73e09c8f 2
c46325ea 3use 5.008;
7473853a 4
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5use strict;
6use warnings;
73e09c8f 7
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8use Scalar::Util qw(reftype refaddr blessed);
9
2e58fc35 10our $VERSION = '1.27';
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11my $XS_VERSION = $VERSION;
12$VERSION = eval $VERSION;
13
14# Declare that we have been loaded
15$threads::shared::threads_shared = 1;
16
17# Load the XS code, if applicable
18if ($threads::threads) {
19 require XSLoader;
20 XSLoader::load('threads::shared', $XS_VERSION);
21
22 *is_shared = \&_id;
23
24} else {
25 # String eval is generally evil, but we don't want these subs to
26 # exist at all if 'threads' is not loaded successfully.
27 # Vivifying them conditionally this way saves on average about 4K
28 # of memory per thread.
29 eval <<'_MARKER_';
30 sub share (\[$@%]) { return $_[0] }
31 sub is_shared (\[$@%]) { undef }
32 sub cond_wait (\[$@%];\[$@%]) { undef }
33 sub cond_timedwait (\[$@%]$;\[$@%]) { undef }
34 sub cond_signal (\[$@%]) { undef }
35 sub cond_broadcast (\[$@%]) { undef }
36_MARKER_
37}
38
39
40### Export ###
41
42sub import
43{
44 # Exported subroutines
45 my @EXPORT = qw(share is_shared cond_wait cond_timedwait
373098c0 46 cond_signal cond_broadcast shared_clone);
5c360ac5 47 if ($threads::threads) {
7473853a 48 push(@EXPORT, 'bless');
5c360ac5 49 }
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50
51 # Export subroutine names
52 my $caller = caller();
53 foreach my $sym (@EXPORT) {
54 no strict 'refs';
55 *{$caller.'::'.$sym} = \&{$sym};
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56 }
57}
b050c948 58
7473853a 59
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60# Predeclarations for internal functions
61my ($make_shared);
62
63
7473853a 64### Methods, etc. ###
dab065ea 65
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66sub threads::shared::tie::SPLICE
67{
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68 require Carp;
69 Carp::croak('Splice not implemented for shared arrays');
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70}
71
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72
73# Create a thread-shared clone of a complex data structure or object
74sub shared_clone
75{
76 if (@_ != 1) {
77 require Carp;
78 Carp::croak('Usage: shared_clone(REF)');
79 }
80
81 return $make_shared->(shift, {});
82}
83
84
85### Internal Functions ###
86
87# Used by shared_clone() to recursively clone
88# a complex data structure or object
89$make_shared = sub {
90 my ($item, $cloned) = @_;
91
92 # Just return the item if:
93 # 1. Not a ref;
94 # 2. Already shared; or
95 # 3. Not running 'threads'.
96 return $item if (! ref($item) || is_shared($item) || ! $threads::threads);
97
98 # Check for previously cloned references
99 # (this takes care of circular refs as well)
100 my $addr = refaddr($item);
101 if (exists($cloned->{$addr})) {
102 # Return the already existing clone
103 return $cloned->{$addr};
104 }
105
106 # Make copies of array, hash and scalar refs and refs of refs
107 my $copy;
108 my $ref_type = reftype($item);
109
110 # Copy an array ref
111 if ($ref_type eq 'ARRAY') {
112 # Make empty shared array ref
113 $copy = &share([]);
114 # Add to clone checking hash
115 $cloned->{$addr} = $copy;
116 # Recursively copy and add contents
117 push(@$copy, map { $make_shared->($_, $cloned) } @$item);
118 }
119
120 # Copy a hash ref
121 elsif ($ref_type eq 'HASH') {
122 # Make empty shared hash ref
123 $copy = &share({});
124 # Add to clone checking hash
125 $cloned->{$addr} = $copy;
126 # Recursively copy and add contents
127 foreach my $key (keys(%{$item})) {
128 $copy->{$key} = $make_shared->($item->{$key}, $cloned);
129 }
130 }
131
132 # Copy a scalar ref
133 elsif ($ref_type eq 'SCALAR') {
134 $copy = \do{ my $scalar = $$item; };
135 share($copy);
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136 # Add to clone checking hash
137 $cloned->{$addr} = $copy;
138 }
139
140 # Copy of a ref of a ref
141 elsif ($ref_type eq 'REF') {
142 # Special handling for $x = \$x
143 if ($addr == refaddr($$item)) {
144 $copy = \$copy;
145 share($copy);
146 $cloned->{$addr} = $copy;
147 } else {
148 my $tmp;
149 $copy = \$tmp;
150 share($copy);
151 # Add to clone checking hash
152 $cloned->{$addr} = $copy;
153 # Recursively copy and add contents
154 $tmp = $make_shared->($$item, $cloned);
155 }
156
157 } else {
158 require Carp;
159 Carp::croak("Unsupported ref type: ", $ref_type);
160 }
161
162 # If input item is an object, then bless the copy into the same class
163 if (my $class = blessed($item)) {
164 bless($copy, $class);
165 }
166
167 # Clone READONLY flag
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168 if ($ref_type eq 'SCALAR') {
169 if (Internals::SvREADONLY($$item)) {
170 Internals::SvREADONLY($$copy, 1) if ($] >= 5.008003);
171 }
172 }
373098c0 173 if (Internals::SvREADONLY($item)) {
a469502f 174 Internals::SvREADONLY($copy, 1) if ($] >= 5.008003);
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175 }
176
177 return $copy;
178};
179
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1801;
181
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182__END__
183
184=head1 NAME
185
186threads::shared - Perl extension for sharing data structures between threads
187
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188=head1 VERSION
189
2e58fc35 190This document describes threads::shared version 1.27
7473853a 191
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192=head1 SYNOPSIS
193
73e09c8f 194 use threads;
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195 use threads::shared;
196
7473853a 197 my $var :shared;
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198 my %hsh :shared;
199 my @ary :shared;
38875929 200
3b29be8d 201 my ($scalar, @array, %hash);
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202 share($scalar);
203 share(@array);
aaf3876d 204 share(%hash);
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205
206 $var = $scalar_value;
207 $var = $shared_ref_value;
208 $var = shared_clone($non_shared_ref_value);
209 $var = shared_clone({'foo' => [qw/foo bar baz/]});
210
211 $hsh{'foo'} = $scalar_value;
212 $hsh{'bar'} = $shared_ref_value;
213 $hsh{'baz'} = shared_clone($non_shared_ref_value);
214 $hsh{'quz'} = shared_clone([1..3]);
215
216 $ary[0] = $scalar_value;
217 $ary[1] = $shared_ref_value;
218 $ary[2] = shared_clone($non_shared_ref_value);
219 $ary[3] = shared_clone([ {}, [] ]);
b050c948 220
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221 { lock(%hash); ... }
222
b050c948 223 cond_wait($scalar);
a0e036c1 224 cond_timedwait($scalar, time() + 30);
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225 cond_broadcast(@array);
226 cond_signal(%hash);
b050c948 227
7473853a 228 my $lockvar :shared;
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229 # condition var != lock var
230 cond_wait($var, $lockvar);
231 cond_timedwait($var, time()+30, $lockvar);
232
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233=head1 DESCRIPTION
234
38875929 235By default, variables are private to each thread, and each newly created
7473853a 236thread gets a private copy of each existing variable. This module allows you
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237to share variables across different threads (and pseudo-forks on Win32). It
238is used together with the L<threads> module.
239
240This module supports the sharing of the following data types only: scalars
241and scalar refs, arrays and array refs, and hashes and hash refs.
b050c948 242
515f0976 243=head1 EXPORT
b050c948 244
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245The following functions are exported by this module: C<share>,
246C<shared_clone>, C<is_shared>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>
247and C<cond_broadcast>
515f0976 248
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249Note that if this module is imported when L<threads> has not yet been loaded,
250then these functions all become no-ops. This makes it possible to write
251modules that will work in both threaded and non-threaded environments.
e67b86b3 252
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253=head1 FUNCTIONS
254
255=over 4
256
257=item share VARIABLE
258
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259C<share> takes a variable and marks it as shared:
260
261 my ($scalar, @array, %hash);
262 share($scalar);
263 share(@array);
264 share(%hash);
265
266C<share> will return the shared rvalue, but always as a reference.
515f0976 267
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268Variables can also be marked as shared at compile time by using the
269C<:shared> attribute:
38875929 270
373098c0 271 my ($var, %hash, @array) :shared;
caf25f3b 272
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273Shared variables can only store scalars, refs of shared variables, or
274refs of shared data (discussed in next section):
7473853a 275
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276 my ($var, %hash, @array) :shared;
277 my $bork;
278
279 # Storing scalars
280 $var = 1;
281 $hash{'foo'} = 'bar';
282 $array[0] = 1.5;
283
284 # Storing shared refs
285 $var = \%hash;
286 $hash{'ary'} = \@array;
287 $array[1] = \$var;
288
289 # The following are errors:
290 # $var = \$bork; # ref of non-shared variable
291 # $hash{'bork'} = []; # non-shared array ref
292 # push(@array, { 'x' => 1 }); # non-shared hash ref
7473853a 293
373098c0 294=item shared_clone REF
ca5ff8b2 295
373098c0 296C<shared_clone> takes a reference, and returns a shared version of its
2e58fc35 297argument, performing a deep copy on any non-shared elements. Any shared
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298elements in the argument are used as is (i.e., they are not cloned).
299
300 my $cpy = shared_clone({'foo' => [qw/foo bar baz/]});
301
302Object status (i.e., the class an object is blessed into) is also cloned.
303
304 my $obj = {'foo' => [qw/foo bar baz/]};
305 bless($obj, 'Foo');
306 my $cpy = shared_clone($obj);
307 print(ref($cpy), "\n"); # Outputs 'Foo'
308
309For cloning empty array or hash refs, the following may also be used:
310
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311 $var = &share([]); # Same as $var = shared_clone([]);
312 $var = &share({}); # Same as $var = shared_clone({});
ca5ff8b2 313
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314=item is_shared VARIABLE
315
316C<is_shared> checks if the specified variable is shared or not. If shared,
317returns the variable's internal ID (similar to
318L<refaddr()|Scalar::Util/"refaddr EXPR">). Otherwise, returns C<undef>.
319
320 if (is_shared($var)) {
321 print("\$var is shared\n");
322 } else {
323 print("\$var is not shared\n");
324 }
ca5ff8b2 325
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326=item lock VARIABLE
327
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328C<lock> places a lock on a variable until the lock goes out of scope. If the
329variable is locked by another thread, the C<lock> call will block until it's
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330available. Multiple calls to C<lock> by the same thread from within
331dynamically nested scopes are safe -- the variable will remain locked until
332the outermost lock on the variable goes out of scope.
7473853a 333
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334Locking a container object, such as a hash or array, doesn't lock the elements
335of that container. For example, if a thread does a C<lock(@a)>, any other
336thread doing a C<lock($a[12])> won't block.
515f0976 337
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338C<lock()> follows references exactly I<one> level. C<lock(\$a)> is equivalent
339to C<lock($a)>, while C<lock(\\$a)> is not.
515f0976 340
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341Note that you cannot explicitly unlock a variable; you can only wait for the
342lock to go out of scope. This is most easily accomplished by locking the
343variable inside a block.
515f0976 344
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345 my $var :shared;
346 {
347 lock($var);
348 # $var is locked from here to the end of the block
349 ...
350 }
351 # $var is now unlocked
352
353If you need more fine-grained control over shared variable access, see
354L<Thread::Semaphore>.
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355
356=item cond_wait VARIABLE
357
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358=item cond_wait CONDVAR, LOCKVAR
359
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360The C<cond_wait> function takes a B<locked> variable as a parameter, unlocks
361the variable, and blocks until another thread does a C<cond_signal> or
362C<cond_broadcast> for that same locked variable. The variable that
363C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied. If
364there are multiple threads C<cond_wait>ing on the same variable, all but one
7c8caac0 365will re-block waiting to reacquire the lock on the variable. (So if you're only
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366using C<cond_wait> for synchronisation, give up the lock as soon as possible).
367The two actions of unlocking the variable and entering the blocked wait state
368are atomic, the two actions of exiting from the blocked wait state and
7c8caac0 369re-locking the variable are not.
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370
371In its second form, C<cond_wait> takes a shared, B<unlocked> variable followed
372by a shared, B<locked> variable. The second variable is unlocked and thread
373execution suspended until another thread signals the first variable.
374
375It is important to note that the variable can be notified even if no thread
376C<cond_signal> or C<cond_broadcast> on the variable. It is therefore
377important to check the value of the variable and go back to waiting if the
378requirement is not fulfilled. For example, to pause until a shared counter
379drops to zero:
380
381 { lock($counter); cond_wait($count) until $counter == 0; }
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382
383=item cond_timedwait VARIABLE, ABS_TIMEOUT
384
385=item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR
386
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387In its two-argument form, C<cond_timedwait> takes a B<locked> variable and an
388absolute timeout as parameters, unlocks the variable, and blocks until the
389timeout is reached or another thread signals the variable. A false value is
390returned if the timeout is reached, and a true value otherwise. In either
391case, the variable is re-locked upon return.
a0e036c1 392
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393Like C<cond_wait>, this function may take a shared, B<locked> variable as an
394additional parameter; in this case the first parameter is an B<unlocked>
395condition variable protected by a distinct lock variable.
a0e036c1 396
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397Again like C<cond_wait>, waking up and reacquiring the lock are not atomic,
398and you should always check your desired condition after this function
399returns. Since the timeout is an absolute value, however, it does not have to
400be recalculated with each pass:
a0e036c1 401
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402 lock($var);
403 my $abs = time() + 15;
404 until ($ok = desired_condition($var)) {
a0e036c1 405 last if !cond_timedwait($var, $abs);
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406 }
407 # we got it if $ok, otherwise we timed out!
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408
409=item cond_signal VARIABLE
410
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411The C<cond_signal> function takes a B<locked> variable as a parameter and
412unblocks one thread that's C<cond_wait>ing on that variable. If more than one
413thread is blocked in a C<cond_wait> on that variable, only one (and which one
414is indeterminate) will be unblocked.
515f0976 415
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416If there are no threads blocked in a C<cond_wait> on the variable, the signal
417is discarded. By always locking before signaling, you can (with care), avoid
418signaling before another thread has entered cond_wait().
38875929 419
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420C<cond_signal> will normally generate a warning if you attempt to use it on an
421unlocked variable. On the rare occasions where doing this may be sensible, you
ba2940ce 422can suppress the warning with:
38875929 423
7473853a 424 { no warnings 'threads'; cond_signal($foo); }
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425
426=item cond_broadcast VARIABLE
427
428The C<cond_broadcast> function works similarly to C<cond_signal>.
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429C<cond_broadcast>, though, will unblock B<all> the threads that are blocked in
430a C<cond_wait> on the locked variable, rather than only one.
b050c948 431
4cab98c0 432=back
dab065ea 433
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434=head1 OBJECTS
435
436L<threads::shared> exports a version of L<bless()|perlfunc/"bless REF"> that
2b936299 437works on shared objects such that I<blessings> propagate across threads.
7473853a 438
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439 # Create a shared 'Foo' object
440 my $foo :shared = shared_clone({});
441 bless($foo, 'Foo');
7473853a 442
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443 # Create a shared 'Bar' object
444 my $bar :shared = shared_clone({});
445 bless($bar, 'Bar');
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446
447 # Put 'bar' inside 'foo'
448 $foo->{'bar'} = $bar;
449
450 # Rebless the objects via a thread
451 threads->create(sub {
452 # Rebless the outer object
373098c0 453 bless($foo, 'Yin');
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454
455 # Cannot directly rebless the inner object
373098c0 456 #bless($foo->{'bar'}, 'Yang');
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457
458 # Retrieve and rebless the inner object
459 my $obj = $foo->{'bar'};
373098c0 460 bless($obj, 'Yang');
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461 $foo->{'bar'} = $obj;
462
463 })->join();
464
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465 print(ref($foo), "\n"); # Prints 'Yin'
466 print(ref($foo->{'bar'}), "\n"); # Prints 'Yang'
467 print(ref($bar), "\n"); # Also prints 'Yang'
7473853a 468
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469=head1 NOTES
470
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471L<threads::shared> is designed to disable itself silently if threads are not
472available. This allows you to write modules and packages that can be used
473in both threaded and non-threaded applications.
474
475If you want access to threads, you must C<use threads> before you
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476C<use threads::shared>. L<threads> will emit a warning if you use it after
477L<threads::shared>.
dab065ea 478
7473853a 479=head1 BUGS AND LIMITATIONS
b050c948 480
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481When C<share> is used on arrays, hashes, array refs or hash refs, any data
482they contain will be lost.
515f0976 483
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484 my @arr = qw(foo bar baz);
485 share(@arr);
486 # @arr is now empty (i.e., == ());
b050c948 487
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488 # Create a 'foo' object
489 my $foo = { 'data' => 99 };
490 bless($foo, 'foo');
58122748 491
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492 # Share the object
493 share($foo); # Contents are now wiped out
494 print("ERROR: \$foo is empty\n")
495 if (! exists($foo->{'data'}));
3d32476b 496
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497Therefore, populate such variables B<after> declaring them as shared. (Scalar
498and scalar refs are not affected by this problem.)
499
500It is often not wise to share an object unless the class itself has been
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501written to support sharing. For example, an object's destructor may get
502called multiple times, once for each thread's scope exit. Another danger is
503that the contents of hash-based objects will be lost due to the above
504mentioned limitation. See F<examples/class.pl> (in the CPAN distribution of
505this module) for how to create a class that supports object sharing.
b050c948 506
7473853a 507Does not support C<splice> on arrays!
b050c948 508
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509Taking references to the elements of shared arrays and hashes does not
510autovivify the elements, and neither does slicing a shared array/hash over
511non-existent indices/keys autovivify the elements.
512
513C<share()> allows you to C<< share($hashref->{key}) >> without giving any
514error message. But the C<< $hashref->{key} >> is B<not> shared, causing the
515error "locking can only be used on shared values" to occur when you attempt to
516C<< lock($hasref->{key}) >>.
b050c948 517
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518Using L<refaddr()|Scalar::Util/"refaddr EXPR">) is unreliable for testing
519whether or not two shared references are equivalent (e.g., when testing for
520circular references). Use L<is_shared()/"is_shared VARIABLE">, instead:
521
522 use threads;
523 use threads::shared;
524 use Scalar::Util qw(refaddr);
525
526 # If ref is shared, use threads::shared's internal ID.
527 # Otherwise, use refaddr().
528 my $addr1 = is_shared($ref1) || refaddr($ref1);
529 my $addr2 = is_shared($ref2) || refaddr($ref2);
530
531 if ($addr1 == $addr2) {
532 # The refs are equivalent
533 }
534
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535L<each()|perlfunc/"each HASH"> does not work properly on shared references
536embedded in shared structures. For example:
537
538 my %foo :shared;
539 $foo{'bar'} = shared_clone({'a'=>'x', 'b'=>'y', 'c'=>'z'});
540
541 while (my ($key, $val) = each(%{$foo{'bar'}})) {
542 ...
543 }
544
545Either of the following will work instead:
546
547 my $ref = $foo{'bar'};
548 while (my ($key, $val) = each(%{$ref})) {
549 ...
550 }
551
552 foreach my $key (keys(%{$foo{'bar'}})) {
553 my $val = $foo{'bar'}{$key};
554 ...
555 }
556
7473853a 557View existing bug reports at, and submit any new bugs, problems, patches, etc.
794f4697 558to: L<http://rt.cpan.org/Public/Dist/Display.html?Name=threads-shared>
515f0976 559
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560=head1 SEE ALSO
561
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562L<threads::shared> Discussion Forum on CPAN:
563L<http://www.cpanforum.com/dist/threads-shared>
564
565Annotated POD for L<threads::shared>:
2e58fc35 566L<http://annocpan.org/~JDHEDDEN/threads-shared-1.27/shared.pm>
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567
568Source repository:
569L<http://code.google.com/p/threads-shared/>
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570
571L<threads>, L<perlthrtut>
572
573L<http://www.perl.com/pub/a/2002/06/11/threads.html> and
574L<http://www.perl.com/pub/a/2002/09/04/threads.html>
575
576Perl threads mailing list:
577L<http://lists.cpan.org/showlist.cgi?name=iThreads>
578
579=head1 AUTHOR
580
581Artur Bergman E<lt>sky AT crucially DOT netE<gt>
582
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583Documentation borrowed from the old Thread.pm.
584
585CPAN version produced by Jerry D. Hedden E<lt>jdhedden AT cpan DOT orgE<gt>.
b050c948 586
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587=head1 LICENSE
588
589threads::shared is released under the same license as Perl.
590
b050c948 591=cut