Commit | Line | Data |
b050c948 |
1 | package threads::shared; |
73e09c8f |
2 | |
c46325ea |
3 | use 5.008; |
7473853a |
4 | |
b050c948 |
5 | use strict; |
6 | use warnings; |
73e09c8f |
7 | |
7c8caac0 |
8 | our $VERSION = '1.13'; |
7473853a |
9 | my $XS_VERSION = $VERSION; |
10 | $VERSION = eval $VERSION; |
11 | |
12 | # Declare that we have been loaded |
13 | $threads::shared::threads_shared = 1; |
14 | |
15 | # Load the XS code, if applicable |
16 | if ($threads::threads) { |
17 | require XSLoader; |
18 | XSLoader::load('threads::shared', $XS_VERSION); |
19 | |
20 | *is_shared = \&_id; |
21 | |
22 | } else { |
23 | # String eval is generally evil, but we don't want these subs to |
24 | # exist at all if 'threads' is not loaded successfully. |
25 | # Vivifying them conditionally this way saves on average about 4K |
26 | # of memory per thread. |
27 | eval <<'_MARKER_'; |
28 | sub share (\[$@%]) { return $_[0] } |
29 | sub is_shared (\[$@%]) { undef } |
30 | sub cond_wait (\[$@%];\[$@%]) { undef } |
31 | sub cond_timedwait (\[$@%]$;\[$@%]) { undef } |
32 | sub cond_signal (\[$@%]) { undef } |
33 | sub cond_broadcast (\[$@%]) { undef } |
34 | _MARKER_ |
35 | } |
36 | |
37 | |
38 | ### Export ### |
39 | |
40 | sub import |
41 | { |
42 | # Exported subroutines |
43 | my @EXPORT = qw(share is_shared cond_wait cond_timedwait |
44 | cond_signal cond_broadcast); |
5c360ac5 |
45 | if ($threads::threads) { |
7473853a |
46 | push(@EXPORT, 'bless'); |
5c360ac5 |
47 | } |
7473853a |
48 | |
49 | # Export subroutine names |
50 | my $caller = caller(); |
51 | foreach my $sym (@EXPORT) { |
52 | no strict 'refs'; |
53 | *{$caller.'::'.$sym} = \&{$sym}; |
df5c998e |
54 | } |
55 | } |
b050c948 |
56 | |
7473853a |
57 | |
58 | ### Methods, etc. ### |
dab065ea |
59 | |
6b85e4fe |
60 | sub threads::shared::tie::SPLICE |
61 | { |
7473853a |
62 | require Carp; |
63 | Carp::croak('Splice not implemented for shared arrays'); |
6b85e4fe |
64 | } |
65 | |
7473853a |
66 | 1; |
67 | |
b050c948 |
68 | __END__ |
69 | |
70 | =head1 NAME |
71 | |
72 | threads::shared - Perl extension for sharing data structures between threads |
73 | |
7473853a |
74 | =head1 VERSION |
75 | |
7c8caac0 |
76 | This document describes threads::shared version 1.13 |
7473853a |
77 | |
b050c948 |
78 | =head1 SYNOPSIS |
79 | |
73e09c8f |
80 | use threads; |
b050c948 |
81 | use threads::shared; |
82 | |
7473853a |
83 | my $var :shared; |
ca5ff8b2 |
84 | $var = $scalar_value; |
85 | $var = $shared_ref_value; |
7473853a |
86 | $var = share($simple_unshared_ref_value); |
38875929 |
87 | |
3b29be8d |
88 | my ($scalar, @array, %hash); |
4cab98c0 |
89 | share($scalar); |
90 | share(@array); |
aaf3876d |
91 | share(%hash); |
caf25f3b |
92 | my $bar = &share([]); |
93 | $hash{bar} = &share({}); |
b050c948 |
94 | |
38875929 |
95 | { lock(%hash); ... } |
96 | |
b050c948 |
97 | cond_wait($scalar); |
a0e036c1 |
98 | cond_timedwait($scalar, time() + 30); |
515f0976 |
99 | cond_broadcast(@array); |
100 | cond_signal(%hash); |
b050c948 |
101 | |
7473853a |
102 | my $lockvar :shared; |
a0e036c1 |
103 | # condition var != lock var |
104 | cond_wait($var, $lockvar); |
105 | cond_timedwait($var, time()+30, $lockvar); |
106 | |
b050c948 |
107 | =head1 DESCRIPTION |
108 | |
38875929 |
109 | By default, variables are private to each thread, and each newly created |
7473853a |
110 | thread gets a private copy of each existing variable. This module allows you |
7c8caac0 |
111 | to share variables across different threads (and pseudo-forks on Win32). It is |
7473853a |
112 | used together with the L<threads> module. |
b050c948 |
113 | |
515f0976 |
114 | =head1 EXPORT |
b050c948 |
115 | |
7473853a |
116 | C<share>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>, C<cond_broadcast>, |
117 | C<is_shared> |
515f0976 |
118 | |
7473853a |
119 | Note that if this module is imported when L<threads> has not yet been loaded, |
120 | then these functions all become no-ops. This makes it possible to write |
121 | modules that will work in both threaded and non-threaded environments. |
e67b86b3 |
122 | |
515f0976 |
123 | =head1 FUNCTIONS |
124 | |
125 | =over 4 |
126 | |
127 | =item share VARIABLE |
128 | |
7473853a |
129 | C<share> takes a value and marks it as shared. You can share a scalar, array, |
130 | hash, scalar ref, array ref, or hash ref. C<share> will return the shared |
131 | rvalue, but always as a reference. |
515f0976 |
132 | |
38875929 |
133 | A variable can also be marked as shared at compile time by using the |
7473853a |
134 | C<:shared> attribute: C<my $var :shared;>. |
38875929 |
135 | |
7473853a |
136 | Due to problems with Perl's prototyping, if you want to share a newly created |
137 | reference, you need to use the C<&share([])> and C<&share({})> syntax. |
caf25f3b |
138 | |
ca5ff8b2 |
139 | The only values that can be assigned to a shared scalar are other scalar |
7473853a |
140 | values, or shared refs: |
141 | |
142 | my $var :shared; |
143 | $var = 1; # ok |
144 | $var = []; # error |
145 | $var = &share([]); # ok |
146 | |
147 | C<share> will traverse up references exactly I<one> level. C<share(\$a)> is |
148 | equivalent to C<share($a)>, while C<share(\\$a)> is not. This means that you |
149 | must create nested shared data structures by first creating individual shared |
150 | leaf nodes, and then adding them to a shared hash or array. |
ca5ff8b2 |
151 | |
7473853a |
152 | my %hash :shared; |
153 | $hash{'meaning'} = &share([]); |
154 | $hash{'meaning'}[0] = &share({}); |
155 | $hash{'meaning'}[0]{'life'} = 42; |
ca5ff8b2 |
156 | |
7473853a |
157 | =item is_shared VARIABLE |
158 | |
159 | C<is_shared> checks if the specified variable is shared or not. If shared, |
160 | returns the variable's internal ID (similar to |
161 | L<refaddr()|Scalar::Util/"refaddr EXPR">). Otherwise, returns C<undef>. |
162 | |
163 | if (is_shared($var)) { |
164 | print("\$var is shared\n"); |
165 | } else { |
166 | print("\$var is not shared\n"); |
167 | } |
ca5ff8b2 |
168 | |
515f0976 |
169 | =item lock VARIABLE |
170 | |
7473853a |
171 | C<lock> places a lock on a variable until the lock goes out of scope. If the |
172 | variable is locked by another thread, the C<lock> call will block until it's |
2b936299 |
173 | available. Multiple calls to C<lock> by the same thread from within |
174 | dynamically nested scopes are safe -- the variable will remain locked until |
175 | the outermost lock on the variable goes out of scope. |
7473853a |
176 | |
2b936299 |
177 | Locking a container object, such as a hash or array, doesn't lock the elements |
178 | of that container. For example, if a thread does a C<lock(@a)>, any other |
179 | thread doing a C<lock($a[12])> won't block. |
515f0976 |
180 | |
2b936299 |
181 | C<lock()> follows references exactly I<one> level. C<lock(\$a)> is equivalent |
182 | to C<lock($a)>, while C<lock(\\$a)> is not. |
515f0976 |
183 | |
7473853a |
184 | Note that you cannot explicitly unlock a variable; you can only wait for the |
185 | lock to go out of scope. This is most easily accomplished by locking the |
186 | variable inside a block. |
515f0976 |
187 | |
7473853a |
188 | my $var :shared; |
189 | { |
190 | lock($var); |
191 | # $var is locked from here to the end of the block |
192 | ... |
193 | } |
194 | # $var is now unlocked |
195 | |
196 | If you need more fine-grained control over shared variable access, see |
197 | L<Thread::Semaphore>. |
515f0976 |
198 | |
199 | =item cond_wait VARIABLE |
200 | |
a0e036c1 |
201 | =item cond_wait CONDVAR, LOCKVAR |
202 | |
7473853a |
203 | The C<cond_wait> function takes a B<locked> variable as a parameter, unlocks |
204 | the variable, and blocks until another thread does a C<cond_signal> or |
205 | C<cond_broadcast> for that same locked variable. The variable that |
206 | C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied. If |
207 | there are multiple threads C<cond_wait>ing on the same variable, all but one |
7c8caac0 |
208 | will re-block waiting to reacquire the lock on the variable. (So if you're only |
7473853a |
209 | using C<cond_wait> for synchronisation, give up the lock as soon as possible). |
210 | The two actions of unlocking the variable and entering the blocked wait state |
211 | are atomic, the two actions of exiting from the blocked wait state and |
7c8caac0 |
212 | re-locking the variable are not. |
7473853a |
213 | |
214 | In its second form, C<cond_wait> takes a shared, B<unlocked> variable followed |
215 | by a shared, B<locked> variable. The second variable is unlocked and thread |
216 | execution suspended until another thread signals the first variable. |
217 | |
218 | It is important to note that the variable can be notified even if no thread |
219 | C<cond_signal> or C<cond_broadcast> on the variable. It is therefore |
220 | important to check the value of the variable and go back to waiting if the |
221 | requirement is not fulfilled. For example, to pause until a shared counter |
222 | drops to zero: |
223 | |
224 | { lock($counter); cond_wait($count) until $counter == 0; } |
a0e036c1 |
225 | |
226 | =item cond_timedwait VARIABLE, ABS_TIMEOUT |
227 | |
228 | =item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR |
229 | |
7473853a |
230 | In its two-argument form, C<cond_timedwait> takes a B<locked> variable and an |
231 | absolute timeout as parameters, unlocks the variable, and blocks until the |
232 | timeout is reached or another thread signals the variable. A false value is |
233 | returned if the timeout is reached, and a true value otherwise. In either |
234 | case, the variable is re-locked upon return. |
a0e036c1 |
235 | |
7473853a |
236 | Like C<cond_wait>, this function may take a shared, B<locked> variable as an |
237 | additional parameter; in this case the first parameter is an B<unlocked> |
238 | condition variable protected by a distinct lock variable. |
a0e036c1 |
239 | |
7473853a |
240 | Again like C<cond_wait>, waking up and reacquiring the lock are not atomic, |
241 | and you should always check your desired condition after this function |
242 | returns. Since the timeout is an absolute value, however, it does not have to |
243 | be recalculated with each pass: |
a0e036c1 |
244 | |
7473853a |
245 | lock($var); |
246 | my $abs = time() + 15; |
247 | until ($ok = desired_condition($var)) { |
a0e036c1 |
248 | last if !cond_timedwait($var, $abs); |
7473853a |
249 | } |
250 | # we got it if $ok, otherwise we timed out! |
515f0976 |
251 | |
252 | =item cond_signal VARIABLE |
253 | |
7473853a |
254 | The C<cond_signal> function takes a B<locked> variable as a parameter and |
255 | unblocks one thread that's C<cond_wait>ing on that variable. If more than one |
256 | thread is blocked in a C<cond_wait> on that variable, only one (and which one |
257 | is indeterminate) will be unblocked. |
515f0976 |
258 | |
7473853a |
259 | If there are no threads blocked in a C<cond_wait> on the variable, the signal |
260 | is discarded. By always locking before signaling, you can (with care), avoid |
261 | signaling before another thread has entered cond_wait(). |
38875929 |
262 | |
7473853a |
263 | C<cond_signal> will normally generate a warning if you attempt to use it on an |
264 | unlocked variable. On the rare occasions where doing this may be sensible, you |
ba2940ce |
265 | can suppress the warning with: |
38875929 |
266 | |
7473853a |
267 | { no warnings 'threads'; cond_signal($foo); } |
515f0976 |
268 | |
269 | =item cond_broadcast VARIABLE |
270 | |
271 | The C<cond_broadcast> function works similarly to C<cond_signal>. |
7473853a |
272 | C<cond_broadcast>, though, will unblock B<all> the threads that are blocked in |
273 | a C<cond_wait> on the locked variable, rather than only one. |
b050c948 |
274 | |
4cab98c0 |
275 | =back |
dab065ea |
276 | |
7473853a |
277 | =head1 OBJECTS |
278 | |
279 | L<threads::shared> exports a version of L<bless()|perlfunc/"bless REF"> that |
2b936299 |
280 | works on shared objects such that I<blessings> propagate across threads. |
7473853a |
281 | |
282 | # Create a shared 'foo' object |
283 | my $foo; |
284 | share($foo); |
285 | $foo = &share({}); |
286 | bless($foo, 'foo'); |
287 | |
288 | # Create a shared 'bar' object |
289 | my $bar; |
290 | share($bar); |
291 | $bar = &share({}); |
292 | bless($bar, 'bar'); |
293 | |
294 | # Put 'bar' inside 'foo' |
295 | $foo->{'bar'} = $bar; |
296 | |
297 | # Rebless the objects via a thread |
298 | threads->create(sub { |
299 | # Rebless the outer object |
300 | bless($foo, 'yin'); |
301 | |
302 | # Cannot directly rebless the inner object |
303 | #bless($foo->{'bar'}, 'yang'); |
304 | |
305 | # Retrieve and rebless the inner object |
306 | my $obj = $foo->{'bar'}; |
307 | bless($obj, 'yang'); |
308 | $foo->{'bar'} = $obj; |
309 | |
310 | })->join(); |
311 | |
312 | print(ref($foo), "\n"); # Prints 'yin' |
313 | print(ref($foo->{'bar'}), "\n"); # Prints 'yang' |
314 | print(ref($bar), "\n"); # Also prints 'yang' |
315 | |
dab065ea |
316 | =head1 NOTES |
317 | |
7473853a |
318 | threads::shared is designed to disable itself silently if threads are not |
319 | available. If you want access to threads, you must C<use threads> before you |
320 | C<use threads::shared>. L<threads> will emit a warning if you use it after |
321 | L<threads::shared>. |
dab065ea |
322 | |
7473853a |
323 | =head1 BUGS AND LIMITATIONS |
b050c948 |
324 | |
7473853a |
325 | When C<share> is used on arrays, hashes, array refs or hash refs, any data |
326 | they contain will be lost. |
515f0976 |
327 | |
7473853a |
328 | my @arr = qw(foo bar baz); |
329 | share(@arr); |
330 | # @arr is now empty (i.e., == ()); |
b050c948 |
331 | |
7473853a |
332 | # Create a 'foo' object |
333 | my $foo = { 'data' => 99 }; |
334 | bless($foo, 'foo'); |
58122748 |
335 | |
7473853a |
336 | # Share the object |
337 | share($foo); # Contents are now wiped out |
338 | print("ERROR: \$foo is empty\n") |
339 | if (! exists($foo->{'data'})); |
3d32476b |
340 | |
7473853a |
341 | Therefore, populate such variables B<after> declaring them as shared. (Scalar |
342 | and scalar refs are not affected by this problem.) |
343 | |
344 | It is often not wise to share an object unless the class itself has been |
2b936299 |
345 | written to support sharing. For example, an object's destructor may get |
346 | called multiple times, once for each thread's scope exit. Another danger is |
347 | that the contents of hash-based objects will be lost due to the above |
348 | mentioned limitation. See F<examples/class.pl> (in the CPAN distribution of |
349 | this module) for how to create a class that supports object sharing. |
b050c948 |
350 | |
7473853a |
351 | Does not support C<splice> on arrays! |
b050c948 |
352 | |
7473853a |
353 | Taking references to the elements of shared arrays and hashes does not |
354 | autovivify the elements, and neither does slicing a shared array/hash over |
355 | non-existent indices/keys autovivify the elements. |
356 | |
357 | C<share()> allows you to C<< share($hashref->{key}) >> without giving any |
358 | error message. But the C<< $hashref->{key} >> is B<not> shared, causing the |
359 | error "locking can only be used on shared values" to occur when you attempt to |
360 | C<< lock($hasref->{key}) >>. |
b050c948 |
361 | |
7473853a |
362 | View existing bug reports at, and submit any new bugs, problems, patches, etc. |
363 | to: L<http://rt.cpan.org/NoAuth/Bugs.html?Dist=threads-shared> |
515f0976 |
364 | |
b050c948 |
365 | =head1 SEE ALSO |
366 | |
7473853a |
367 | L<threads::shared> Discussion Forum on CPAN: |
368 | L<http://www.cpanforum.com/dist/threads-shared> |
369 | |
370 | Annotated POD for L<threads::shared>: |
7c8caac0 |
371 | L<http://annocpan.org/~JDHEDDEN/threads-shared-1.13/shared.pm> |
05b59262 |
372 | |
373 | Source repository: |
374 | L<http://code.google.com/p/threads-shared/> |
7473853a |
375 | |
376 | L<threads>, L<perlthrtut> |
377 | |
378 | L<http://www.perl.com/pub/a/2002/06/11/threads.html> and |
379 | L<http://www.perl.com/pub/a/2002/09/04/threads.html> |
380 | |
381 | Perl threads mailing list: |
382 | L<http://lists.cpan.org/showlist.cgi?name=iThreads> |
383 | |
384 | =head1 AUTHOR |
385 | |
386 | Artur Bergman E<lt>sky AT crucially DOT netE<gt> |
387 | |
388 | threads::shared is released under the same license as Perl. |
389 | |
390 | Documentation borrowed from the old Thread.pm. |
391 | |
392 | CPAN version produced by Jerry D. Hedden E<lt>jdhedden AT cpan DOT orgE<gt>. |
b050c948 |
393 | |
394 | =cut |