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1 | package threads::shared; |
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2 | |
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3 | use 5.008; |
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4 | |
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5 | use strict; |
6 | use warnings; |
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7 | |
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8 | use Scalar::Util qw(reftype refaddr blessed); |
9 | |
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10 | our $VERSION = '1.22'; |
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11 | my $XS_VERSION = $VERSION; |
12 | $VERSION = eval $VERSION; |
13 | |
14 | # Declare that we have been loaded |
15 | $threads::shared::threads_shared = 1; |
16 | |
17 | # Load the XS code, if applicable |
18 | if ($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 (\[$@%]) { undef } |
36 | _MARKER_ |
37 | } |
38 | |
39 | |
40 | ### Export ### |
41 | |
42 | sub import |
43 | { |
44 | # Exported subroutines |
45 | my @EXPORT = qw(share is_shared cond_wait cond_timedwait |
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46 | cond_signal cond_broadcast shared_clone); |
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47 | if ($threads::threads) { |
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48 | push(@EXPORT, 'bless'); |
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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 | } |
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58 | |
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59 | |
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60 | # Predeclarations for internal functions |
61 | my ($make_shared); |
62 | |
63 | |
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64 | ### Methods, etc. ### |
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65 | |
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66 | sub 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 |
74 | sub 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 = $$item; }; |
135 | share($copy); |
136 | # Clone READONLY flag |
137 | if (Internals::SvREADONLY($$item)) { |
138 | Internals::SvREADONLY($$copy, 1); |
139 | } |
140 | # Add to clone checking hash |
141 | $cloned->{$addr} = $copy; |
142 | } |
143 | |
144 | # Copy of a ref of a ref |
145 | elsif ($ref_type eq 'REF') { |
146 | # Special handling for $x = \$x |
147 | if ($addr == refaddr($$item)) { |
148 | $copy = \$copy; |
149 | share($copy); |
150 | $cloned->{$addr} = $copy; |
151 | } else { |
152 | my $tmp; |
153 | $copy = \$tmp; |
154 | share($copy); |
155 | # Add to clone checking hash |
156 | $cloned->{$addr} = $copy; |
157 | # Recursively copy and add contents |
158 | $tmp = $make_shared->($$item, $cloned); |
159 | } |
160 | |
161 | } else { |
162 | require Carp; |
163 | Carp::croak("Unsupported ref type: ", $ref_type); |
164 | } |
165 | |
166 | # If input item is an object, then bless the copy into the same class |
167 | if (my $class = blessed($item)) { |
168 | bless($copy, $class); |
169 | } |
170 | |
171 | # Clone READONLY flag |
172 | if (Internals::SvREADONLY($item)) { |
173 | Internals::SvREADONLY($copy, 1); |
174 | } |
175 | |
176 | return $copy; |
177 | }; |
178 | |
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179 | 1; |
180 | |
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181 | __END__ |
182 | |
183 | =head1 NAME |
184 | |
185 | threads::shared - Perl extension for sharing data structures between threads |
186 | |
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187 | =head1 VERSION |
188 | |
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189 | This document describes threads::shared version 1.22 |
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190 | |
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191 | =head1 SYNOPSIS |
192 | |
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193 | use threads; |
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194 | use threads::shared; |
195 | |
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196 | my $var :shared; |
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197 | my %hsh :shared; |
198 | my @ary :shared; |
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199 | |
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200 | my ($scalar, @array, %hash); |
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201 | share($scalar); |
202 | share(@array); |
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203 | share(%hash); |
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204 | |
205 | $var = $scalar_value; |
206 | $var = $shared_ref_value; |
207 | $var = shared_clone($non_shared_ref_value); |
208 | $var = shared_clone({'foo' => [qw/foo bar baz/]}); |
209 | |
210 | $hsh{'foo'} = $scalar_value; |
211 | $hsh{'bar'} = $shared_ref_value; |
212 | $hsh{'baz'} = shared_clone($non_shared_ref_value); |
213 | $hsh{'quz'} = shared_clone([1..3]); |
214 | |
215 | $ary[0] = $scalar_value; |
216 | $ary[1] = $shared_ref_value; |
217 | $ary[2] = shared_clone($non_shared_ref_value); |
218 | $ary[3] = shared_clone([ {}, [] ]); |
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219 | |
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220 | { lock(%hash); ... } |
221 | |
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222 | cond_wait($scalar); |
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223 | cond_timedwait($scalar, time() + 30); |
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224 | cond_broadcast(@array); |
225 | cond_signal(%hash); |
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226 | |
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227 | my $lockvar :shared; |
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228 | # condition var != lock var |
229 | cond_wait($var, $lockvar); |
230 | cond_timedwait($var, time()+30, $lockvar); |
231 | |
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232 | =head1 DESCRIPTION |
233 | |
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234 | By default, variables are private to each thread, and each newly created |
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235 | thread gets a private copy of each existing variable. This module allows you |
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236 | to share variables across different threads (and pseudo-forks on Win32). It |
237 | is used together with the L<threads> module. |
238 | |
239 | This module supports the sharing of the following data types only: scalars |
240 | and scalar refs, arrays and array refs, and hashes and hash refs. |
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241 | |
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242 | =head1 EXPORT |
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243 | |
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244 | The following functions are exported by this module: C<share>, |
245 | C<shared_clone>, C<is_shared>, C<cond_wait>, C<cond_timedwait>, C<cond_signal> |
246 | and C<cond_broadcast> |
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247 | |
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248 | Note that if this module is imported when L<threads> has not yet been loaded, |
249 | then these functions all become no-ops. This makes it possible to write |
250 | modules that will work in both threaded and non-threaded environments. |
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251 | |
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252 | =head1 FUNCTIONS |
253 | |
254 | =over 4 |
255 | |
256 | =item share VARIABLE |
257 | |
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258 | C<share> takes a variable and marks it as shared: |
259 | |
260 | my ($scalar, @array, %hash); |
261 | share($scalar); |
262 | share(@array); |
263 | share(%hash); |
264 | |
265 | C<share> will return the shared rvalue, but always as a reference. |
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266 | |
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267 | Variables can also be marked as shared at compile time by using the |
268 | C<:shared> attribute: |
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269 | |
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270 | my ($var, %hash, @array) :shared; |
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271 | |
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272 | Shared variables can only store scalars, refs of shared variables, or |
273 | refs of shared data (discussed in next section): |
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274 | |
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275 | my ($var, %hash, @array) :shared; |
276 | my $bork; |
277 | |
278 | # Storing scalars |
279 | $var = 1; |
280 | $hash{'foo'} = 'bar'; |
281 | $array[0] = 1.5; |
282 | |
283 | # Storing shared refs |
284 | $var = \%hash; |
285 | $hash{'ary'} = \@array; |
286 | $array[1] = \$var; |
287 | |
288 | # The following are errors: |
289 | # $var = \$bork; # ref of non-shared variable |
290 | # $hash{'bork'} = []; # non-shared array ref |
291 | # push(@array, { 'x' => 1 }); # non-shared hash ref |
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292 | |
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293 | =item shared_clone REF |
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294 | |
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295 | C<shared_clone> takes a reference, and returns a shared version of its |
296 | argument, preforming a deep copy on any non-shared elements. Any shared |
297 | elements in the argument are used as is (i.e., they are not cloned). |
298 | |
299 | my $cpy = shared_clone({'foo' => [qw/foo bar baz/]}); |
300 | |
301 | Object status (i.e., the class an object is blessed into) is also cloned. |
302 | |
303 | my $obj = {'foo' => [qw/foo bar baz/]}; |
304 | bless($obj, 'Foo'); |
305 | my $cpy = shared_clone($obj); |
306 | print(ref($cpy), "\n"); # Outputs 'Foo' |
307 | |
308 | For cloning empty array or hash refs, the following may also be used: |
309 | |
310 | $var = &share([]); # Same as $var = share_clone([]); |
311 | $var = &share({}); # Same as $var = share_clone({}); |
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312 | |
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313 | =item is_shared VARIABLE |
314 | |
315 | C<is_shared> checks if the specified variable is shared or not. If shared, |
316 | returns the variable's internal ID (similar to |
317 | L<refaddr()|Scalar::Util/"refaddr EXPR">). Otherwise, returns C<undef>. |
318 | |
319 | if (is_shared($var)) { |
320 | print("\$var is shared\n"); |
321 | } else { |
322 | print("\$var is not shared\n"); |
323 | } |
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324 | |
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325 | =item lock VARIABLE |
326 | |
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327 | C<lock> places a lock on a variable until the lock goes out of scope. If the |
328 | variable is locked by another thread, the C<lock> call will block until it's |
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329 | available. Multiple calls to C<lock> by the same thread from within |
330 | dynamically nested scopes are safe -- the variable will remain locked until |
331 | the outermost lock on the variable goes out of scope. |
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332 | |
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333 | Locking a container object, such as a hash or array, doesn't lock the elements |
334 | of that container. For example, if a thread does a C<lock(@a)>, any other |
335 | thread doing a C<lock($a[12])> won't block. |
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336 | |
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337 | C<lock()> follows references exactly I<one> level. C<lock(\$a)> is equivalent |
338 | to C<lock($a)>, while C<lock(\\$a)> is not. |
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339 | |
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340 | Note that you cannot explicitly unlock a variable; you can only wait for the |
341 | lock to go out of scope. This is most easily accomplished by locking the |
342 | variable inside a block. |
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343 | |
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344 | my $var :shared; |
345 | { |
346 | lock($var); |
347 | # $var is locked from here to the end of the block |
348 | ... |
349 | } |
350 | # $var is now unlocked |
351 | |
352 | If you need more fine-grained control over shared variable access, see |
353 | L<Thread::Semaphore>. |
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354 | |
355 | =item cond_wait VARIABLE |
356 | |
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357 | =item cond_wait CONDVAR, LOCKVAR |
358 | |
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359 | The C<cond_wait> function takes a B<locked> variable as a parameter, unlocks |
360 | the variable, and blocks until another thread does a C<cond_signal> or |
361 | C<cond_broadcast> for that same locked variable. The variable that |
362 | C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied. If |
363 | there are multiple threads C<cond_wait>ing on the same variable, all but one |
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364 | will re-block waiting to reacquire the lock on the variable. (So if you're only |
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365 | using C<cond_wait> for synchronisation, give up the lock as soon as possible). |
366 | The two actions of unlocking the variable and entering the blocked wait state |
367 | are atomic, the two actions of exiting from the blocked wait state and |
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368 | re-locking the variable are not. |
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369 | |
370 | In its second form, C<cond_wait> takes a shared, B<unlocked> variable followed |
371 | by a shared, B<locked> variable. The second variable is unlocked and thread |
372 | execution suspended until another thread signals the first variable. |
373 | |
374 | It is important to note that the variable can be notified even if no thread |
375 | C<cond_signal> or C<cond_broadcast> on the variable. It is therefore |
376 | important to check the value of the variable and go back to waiting if the |
377 | requirement is not fulfilled. For example, to pause until a shared counter |
378 | drops to zero: |
379 | |
380 | { lock($counter); cond_wait($count) until $counter == 0; } |
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381 | |
382 | =item cond_timedwait VARIABLE, ABS_TIMEOUT |
383 | |
384 | =item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR |
385 | |
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386 | In its two-argument form, C<cond_timedwait> takes a B<locked> variable and an |
387 | absolute timeout as parameters, unlocks the variable, and blocks until the |
388 | timeout is reached or another thread signals the variable. A false value is |
389 | returned if the timeout is reached, and a true value otherwise. In either |
390 | case, the variable is re-locked upon return. |
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391 | |
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392 | Like C<cond_wait>, this function may take a shared, B<locked> variable as an |
393 | additional parameter; in this case the first parameter is an B<unlocked> |
394 | condition variable protected by a distinct lock variable. |
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395 | |
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396 | Again like C<cond_wait>, waking up and reacquiring the lock are not atomic, |
397 | and you should always check your desired condition after this function |
398 | returns. Since the timeout is an absolute value, however, it does not have to |
399 | be recalculated with each pass: |
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400 | |
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401 | lock($var); |
402 | my $abs = time() + 15; |
403 | until ($ok = desired_condition($var)) { |
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404 | last if !cond_timedwait($var, $abs); |
7473853a |
405 | } |
406 | # we got it if $ok, otherwise we timed out! |
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407 | |
408 | =item cond_signal VARIABLE |
409 | |
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410 | The C<cond_signal> function takes a B<locked> variable as a parameter and |
411 | unblocks one thread that's C<cond_wait>ing on that variable. If more than one |
412 | thread is blocked in a C<cond_wait> on that variable, only one (and which one |
413 | is indeterminate) will be unblocked. |
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414 | |
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415 | If there are no threads blocked in a C<cond_wait> on the variable, the signal |
416 | is discarded. By always locking before signaling, you can (with care), avoid |
417 | signaling before another thread has entered cond_wait(). |
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418 | |
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419 | C<cond_signal> will normally generate a warning if you attempt to use it on an |
420 | unlocked variable. On the rare occasions where doing this may be sensible, you |
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421 | can suppress the warning with: |
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422 | |
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423 | { no warnings 'threads'; cond_signal($foo); } |
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424 | |
425 | =item cond_broadcast VARIABLE |
426 | |
427 | The C<cond_broadcast> function works similarly to C<cond_signal>. |
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428 | C<cond_broadcast>, though, will unblock B<all> the threads that are blocked in |
429 | a C<cond_wait> on the locked variable, rather than only one. |
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430 | |
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431 | =back |
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432 | |
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433 | =head1 OBJECTS |
434 | |
435 | L<threads::shared> exports a version of L<bless()|perlfunc/"bless REF"> that |
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436 | works on shared objects such that I<blessings> propagate across threads. |
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437 | |
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438 | # Create a shared 'Foo' object |
439 | my $foo :shared = shared_clone({}); |
440 | bless($foo, 'Foo'); |
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441 | |
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442 | # Create a shared 'Bar' object |
443 | my $bar :shared = shared_clone({}); |
444 | bless($bar, 'Bar'); |
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445 | |
446 | # Put 'bar' inside 'foo' |
447 | $foo->{'bar'} = $bar; |
448 | |
449 | # Rebless the objects via a thread |
450 | threads->create(sub { |
451 | # Rebless the outer object |
373098c0 |
452 | bless($foo, 'Yin'); |
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453 | |
454 | # Cannot directly rebless the inner object |
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455 | #bless($foo->{'bar'}, 'Yang'); |
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456 | |
457 | # Retrieve and rebless the inner object |
458 | my $obj = $foo->{'bar'}; |
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459 | bless($obj, 'Yang'); |
7473853a |
460 | $foo->{'bar'} = $obj; |
461 | |
462 | })->join(); |
463 | |
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464 | print(ref($foo), "\n"); # Prints 'Yin' |
465 | print(ref($foo->{'bar'}), "\n"); # Prints 'Yang' |
466 | print(ref($bar), "\n"); # Also prints 'Yang' |
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467 | |
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468 | =head1 NOTES |
469 | |
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470 | L<threads::shared> is designed to disable itself silently if threads are not |
471 | available. This allows you to write modules and packages that can be used |
472 | in both threaded and non-threaded applications. |
473 | |
474 | If you want access to threads, you must C<use threads> before you |
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475 | C<use threads::shared>. L<threads> will emit a warning if you use it after |
476 | L<threads::shared>. |
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477 | |
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478 | =head1 BUGS AND LIMITATIONS |
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479 | |
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480 | When C<share> is used on arrays, hashes, array refs or hash refs, any data |
481 | they contain will be lost. |
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482 | |
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483 | my @arr = qw(foo bar baz); |
484 | share(@arr); |
485 | # @arr is now empty (i.e., == ()); |
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486 | |
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487 | # Create a 'foo' object |
488 | my $foo = { 'data' => 99 }; |
489 | bless($foo, 'foo'); |
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490 | |
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491 | # Share the object |
492 | share($foo); # Contents are now wiped out |
493 | print("ERROR: \$foo is empty\n") |
494 | if (! exists($foo->{'data'})); |
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495 | |
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496 | Therefore, populate such variables B<after> declaring them as shared. (Scalar |
497 | and scalar refs are not affected by this problem.) |
498 | |
499 | It is often not wise to share an object unless the class itself has been |
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500 | written to support sharing. For example, an object's destructor may get |
501 | called multiple times, once for each thread's scope exit. Another danger is |
502 | that the contents of hash-based objects will be lost due to the above |
503 | mentioned limitation. See F<examples/class.pl> (in the CPAN distribution of |
504 | this module) for how to create a class that supports object sharing. |
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505 | |
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506 | Does not support C<splice> on arrays! |
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507 | |
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508 | Taking references to the elements of shared arrays and hashes does not |
509 | autovivify the elements, and neither does slicing a shared array/hash over |
510 | non-existent indices/keys autovivify the elements. |
511 | |
512 | C<share()> allows you to C<< share($hashref->{key}) >> without giving any |
513 | error message. But the C<< $hashref->{key} >> is B<not> shared, causing the |
514 | error "locking can only be used on shared values" to occur when you attempt to |
515 | C<< lock($hasref->{key}) >>. |
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516 | |
f6d55995 |
517 | Using L<refaddr()|Scalar::Util/"refaddr EXPR">) is unreliable for testing |
518 | whether or not two shared references are equivalent (e.g., when testing for |
519 | circular references). Use L<is_shared()/"is_shared VARIABLE">, instead: |
520 | |
521 | use threads; |
522 | use threads::shared; |
523 | use Scalar::Util qw(refaddr); |
524 | |
525 | # If ref is shared, use threads::shared's internal ID. |
526 | # Otherwise, use refaddr(). |
527 | my $addr1 = is_shared($ref1) || refaddr($ref1); |
528 | my $addr2 = is_shared($ref2) || refaddr($ref2); |
529 | |
530 | if ($addr1 == $addr2) { |
531 | # The refs are equivalent |
532 | } |
533 | |
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534 | View existing bug reports at, and submit any new bugs, problems, patches, etc. |
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535 | to: L<http://rt.cpan.org/Public/Dist/Display.html?Name=threads-shared> |
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536 | |
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537 | =head1 SEE ALSO |
538 | |
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539 | L<threads::shared> Discussion Forum on CPAN: |
540 | L<http://www.cpanforum.com/dist/threads-shared> |
541 | |
542 | Annotated POD for L<threads::shared>: |
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543 | L<http://annocpan.org/~JDHEDDEN/threads-shared-1.22/shared.pm> |
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544 | |
545 | Source repository: |
546 | L<http://code.google.com/p/threads-shared/> |
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547 | |
548 | L<threads>, L<perlthrtut> |
549 | |
550 | L<http://www.perl.com/pub/a/2002/06/11/threads.html> and |
551 | L<http://www.perl.com/pub/a/2002/09/04/threads.html> |
552 | |
553 | Perl threads mailing list: |
554 | L<http://lists.cpan.org/showlist.cgi?name=iThreads> |
555 | |
556 | =head1 AUTHOR |
557 | |
558 | Artur Bergman E<lt>sky AT crucially DOT netE<gt> |
559 | |
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560 | Documentation borrowed from the old Thread.pm. |
561 | |
562 | CPAN version produced by Jerry D. Hedden E<lt>jdhedden AT cpan DOT orgE<gt>. |
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563 | |
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564 | =head1 LICENSE |
565 | |
566 | threads::shared is released under the same license as Perl. |
567 | |
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568 | =cut |