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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 = '1.32'; |
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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 = $$item; }; |
135 | share($copy); |
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136 | # Add to clone checking hash |
137 | $cloned->{$addr} = $copy; |
138 | } |
139 | |
140 | # Copy of a ref of a ref |
141 | elsif ($ref_type eq 'REF') { |
142 | # Special handling for $x = \$x |
143 | if ($addr == refaddr($$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 ($] >= 5.008003); |
171 | } |
172 | } |
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173 | if (Internals::SvREADONLY($item)) { |
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174 | Internals::SvREADONLY($copy, 1) if ($] >= 5.008003); |
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175 | } |
176 | |
177 | return $copy; |
178 | }; |
179 | |
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180 | 1; |
181 | |
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182 | __END__ |
183 | |
184 | =head1 NAME |
185 | |
186 | threads::shared - Perl extension for sharing data structures between threads |
187 | |
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188 | =head1 VERSION |
189 | |
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190 | This document describes threads::shared version 1.32 |
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191 | |
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192 | =head1 SYNOPSIS |
193 | |
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194 | use threads; |
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195 | use threads::shared; |
196 | |
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197 | my $var :shared; |
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198 | my %hsh :shared; |
199 | my @ary :shared; |
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200 | |
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201 | my ($scalar, @array, %hash); |
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202 | share($scalar); |
203 | share(@array); |
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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 | $ary[3] = shared_clone([ {}, [] ]); |
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220 | |
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221 | { lock(%hash); ... } |
222 | |
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223 | cond_wait($scalar); |
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224 | cond_timedwait($scalar, time() + 30); |
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225 | cond_broadcast(@array); |
226 | cond_signal(%hash); |
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227 | |
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228 | my $lockvar :shared; |
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229 | # condition var != lock var |
230 | cond_wait($var, $lockvar); |
231 | cond_timedwait($var, time()+30, $lockvar); |
232 | |
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233 | =head1 DESCRIPTION |
234 | |
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235 | By default, variables are private to each thread, and each newly created |
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236 | thread gets a private copy of each existing variable. This module allows you |
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237 | to share variables across different threads (and pseudo-forks on Win32). It |
238 | is used together with the L<threads> module. |
239 | |
240 | This module supports the sharing of the following data types only: scalars |
241 | and scalar refs, arrays and array refs, and hashes and hash refs. |
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242 | |
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243 | =head1 EXPORT |
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244 | |
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245 | The following functions are exported by this module: C<share>, |
246 | C<shared_clone>, C<is_shared>, C<cond_wait>, C<cond_timedwait>, C<cond_signal> |
247 | and C<cond_broadcast> |
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248 | |
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249 | Note that if this module is imported when L<threads> has not yet been loaded, |
250 | then these functions all become no-ops. This makes it possible to write |
251 | modules that will work in both threaded and non-threaded environments. |
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252 | |
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253 | =head1 FUNCTIONS |
254 | |
255 | =over 4 |
256 | |
257 | =item share VARIABLE |
258 | |
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259 | C<share> takes a variable and marks it as shared: |
260 | |
261 | my ($scalar, @array, %hash); |
262 | share($scalar); |
263 | share(@array); |
264 | share(%hash); |
265 | |
266 | C<share> will return the shared rvalue, but always as a reference. |
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267 | |
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268 | Variables can also be marked as shared at compile time by using the |
269 | C<:shared> attribute: |
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270 | |
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271 | my ($var, %hash, @array) :shared; |
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272 | |
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273 | Shared variables can only store scalars, refs of shared variables, or |
274 | refs of shared data (discussed in next section): |
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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 |
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293 | |
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294 | =item shared_clone REF |
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295 | |
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296 | C<shared_clone> takes a reference, and returns a shared version of its |
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297 | argument, performing a deep copy on any non-shared elements. Any shared |
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298 | elements 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 | |
302 | Object 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 | |
309 | For 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 $var = shared_clone({}); |
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313 | |
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314 | =item is_shared VARIABLE |
315 | |
316 | C<is_shared> checks if the specified variable is shared or not. If shared, |
317 | returns the variable's internal ID (similar to |
318 | L<refaddr()|Scalar::Util/"refaddr EXPR">). Otherwise, returns C<undef>. |
319 | |
320 | if (is_shared($var)) { |
321 | print("\$var is shared\n"); |
322 | } else { |
323 | print("\$var is not shared\n"); |
324 | } |
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325 | |
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326 | When used on an element of an array or hash, C<is_shared> checks if the |
327 | specified element belongs to a shared array or hash. (It does not check |
328 | the contents of that element.) |
329 | |
330 | my %hash :shared; |
331 | if (is_shared(%hash)) { |
332 | print("\%hash is shared\n"); |
333 | } |
334 | |
335 | $hash{'elem'} = 1; |
336 | if (is_shared($hash{'elem'})) { |
337 | print("\$hash{'elem'} is in a shared hash\n"); |
338 | } |
339 | |
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340 | =item lock VARIABLE |
341 | |
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342 | C<lock> places a B<advisory> lock on a variable until the lock goes out of |
343 | scope. If the variable is locked by another thread, the C<lock> call will |
344 | block until it's available. Multiple calls to C<lock> by the same thread from |
345 | within dynamically nested scopes are safe -- the variable will remain locked |
346 | until the outermost lock on the variable goes out of scope. |
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347 | |
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348 | C<lock> follows references exactly I<one> level: |
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349 | |
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350 | my %hash :shared; |
351 | my $ref = \%hash; |
352 | lock($ref); # This is equivalent to lock(%hash) |
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353 | |
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354 | Note that you cannot explicitly unlock a variable; you can only wait for the |
355 | lock to go out of scope. This is most easily accomplished by locking the |
356 | variable inside a block. |
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357 | |
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358 | my $var :shared; |
359 | { |
360 | lock($var); |
361 | # $var is locked from here to the end of the block |
362 | ... |
363 | } |
364 | # $var is now unlocked |
365 | |
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366 | As locks are advisory, they do not prevent data access or modification by |
367 | another thread that does not itself attempt to obtain a lock on the variable. |
368 | |
369 | You cannot lock the individual elements of a container variable: |
370 | |
371 | my %hash :shared; |
372 | $hash{'foo'} = 'bar'; |
373 | #lock($hash{'foo'}); # Error |
374 | lock(%hash); # Works |
375 | |
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376 | If you need more fine-grained control over shared variable access, see |
377 | L<Thread::Semaphore>. |
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378 | |
379 | =item cond_wait VARIABLE |
380 | |
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381 | =item cond_wait CONDVAR, LOCKVAR |
382 | |
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383 | The C<cond_wait> function takes a B<locked> variable as a parameter, unlocks |
384 | the variable, and blocks until another thread does a C<cond_signal> or |
385 | C<cond_broadcast> for that same locked variable. The variable that |
386 | C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied. If |
387 | there are multiple threads C<cond_wait>ing on the same variable, all but one |
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388 | will re-block waiting to reacquire the lock on the variable. (So if you're only |
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389 | using C<cond_wait> for synchronisation, give up the lock as soon as possible). |
390 | The two actions of unlocking the variable and entering the blocked wait state |
391 | are atomic, the two actions of exiting from the blocked wait state and |
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392 | re-locking the variable are not. |
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393 | |
394 | In its second form, C<cond_wait> takes a shared, B<unlocked> variable followed |
395 | by a shared, B<locked> variable. The second variable is unlocked and thread |
396 | execution suspended until another thread signals the first variable. |
397 | |
398 | It is important to note that the variable can be notified even if no thread |
399 | C<cond_signal> or C<cond_broadcast> on the variable. It is therefore |
400 | important to check the value of the variable and go back to waiting if the |
401 | requirement is not fulfilled. For example, to pause until a shared counter |
402 | drops to zero: |
403 | |
63790022 |
404 | { lock($counter); cond_wait($counter) until $counter == 0; } |
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405 | |
406 | =item cond_timedwait VARIABLE, ABS_TIMEOUT |
407 | |
408 | =item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR |
409 | |
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410 | In its two-argument form, C<cond_timedwait> takes a B<locked> variable and an |
411 | absolute timeout as parameters, unlocks the variable, and blocks until the |
412 | timeout is reached or another thread signals the variable. A false value is |
413 | returned if the timeout is reached, and a true value otherwise. In either |
414 | case, the variable is re-locked upon return. |
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415 | |
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416 | Like C<cond_wait>, this function may take a shared, B<locked> variable as an |
417 | additional parameter; in this case the first parameter is an B<unlocked> |
418 | condition variable protected by a distinct lock variable. |
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419 | |
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420 | Again like C<cond_wait>, waking up and reacquiring the lock are not atomic, |
421 | and you should always check your desired condition after this function |
422 | returns. Since the timeout is an absolute value, however, it does not have to |
423 | be recalculated with each pass: |
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424 | |
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425 | lock($var); |
426 | my $abs = time() + 15; |
427 | until ($ok = desired_condition($var)) { |
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428 | last if !cond_timedwait($var, $abs); |
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429 | } |
430 | # we got it if $ok, otherwise we timed out! |
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431 | |
432 | =item cond_signal VARIABLE |
433 | |
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434 | The C<cond_signal> function takes a B<locked> variable as a parameter and |
435 | unblocks one thread that's C<cond_wait>ing on that variable. If more than one |
436 | thread is blocked in a C<cond_wait> on that variable, only one (and which one |
437 | is indeterminate) will be unblocked. |
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438 | |
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439 | If there are no threads blocked in a C<cond_wait> on the variable, the signal |
440 | is discarded. By always locking before signaling, you can (with care), avoid |
441 | signaling before another thread has entered cond_wait(). |
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442 | |
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443 | C<cond_signal> will normally generate a warning if you attempt to use it on an |
444 | unlocked variable. On the rare occasions where doing this may be sensible, you |
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445 | can suppress the warning with: |
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446 | |
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447 | { no warnings 'threads'; cond_signal($foo); } |
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448 | |
449 | =item cond_broadcast VARIABLE |
450 | |
451 | The C<cond_broadcast> function works similarly to C<cond_signal>. |
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452 | C<cond_broadcast>, though, will unblock B<all> the threads that are blocked in |
453 | a C<cond_wait> on the locked variable, rather than only one. |
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454 | |
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455 | =back |
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456 | |
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457 | =head1 OBJECTS |
458 | |
459 | L<threads::shared> exports a version of L<bless()|perlfunc/"bless REF"> that |
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460 | works on shared objects such that I<blessings> propagate across threads. |
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461 | |
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462 | # Create a shared 'Foo' object |
463 | my $foo :shared = shared_clone({}); |
464 | bless($foo, 'Foo'); |
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465 | |
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466 | # Create a shared 'Bar' object |
467 | my $bar :shared = shared_clone({}); |
468 | bless($bar, 'Bar'); |
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469 | |
470 | # Put 'bar' inside 'foo' |
471 | $foo->{'bar'} = $bar; |
472 | |
473 | # Rebless the objects via a thread |
474 | threads->create(sub { |
475 | # Rebless the outer object |
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476 | bless($foo, 'Yin'); |
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477 | |
478 | # Cannot directly rebless the inner object |
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479 | #bless($foo->{'bar'}, 'Yang'); |
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480 | |
481 | # Retrieve and rebless the inner object |
482 | my $obj = $foo->{'bar'}; |
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483 | bless($obj, 'Yang'); |
7473853a |
484 | $foo->{'bar'} = $obj; |
485 | |
486 | })->join(); |
487 | |
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488 | print(ref($foo), "\n"); # Prints 'Yin' |
489 | print(ref($foo->{'bar'}), "\n"); # Prints 'Yang' |
490 | print(ref($bar), "\n"); # Also prints 'Yang' |
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491 | |
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492 | =head1 NOTES |
493 | |
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494 | L<threads::shared> is designed to disable itself silently if threads are not |
495 | available. This allows you to write modules and packages that can be used |
496 | in both threaded and non-threaded applications. |
497 | |
498 | If you want access to threads, you must C<use threads> before you |
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499 | C<use threads::shared>. L<threads> will emit a warning if you use it after |
500 | L<threads::shared>. |
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501 | |
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502 | =head1 BUGS AND LIMITATIONS |
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503 | |
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504 | When C<share> is used on arrays, hashes, array refs or hash refs, any data |
505 | they contain will be lost. |
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506 | |
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507 | my @arr = qw(foo bar baz); |
508 | share(@arr); |
509 | # @arr is now empty (i.e., == ()); |
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510 | |
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511 | # Create a 'foo' object |
512 | my $foo = { 'data' => 99 }; |
513 | bless($foo, 'foo'); |
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514 | |
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515 | # Share the object |
516 | share($foo); # Contents are now wiped out |
517 | print("ERROR: \$foo is empty\n") |
518 | if (! exists($foo->{'data'})); |
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519 | |
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520 | Therefore, populate such variables B<after> declaring them as shared. (Scalar |
521 | and scalar refs are not affected by this problem.) |
522 | |
523 | It is often not wise to share an object unless the class itself has been |
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524 | written to support sharing. For example, an object's destructor may get |
525 | called multiple times, once for each thread's scope exit. Another danger is |
526 | that the contents of hash-based objects will be lost due to the above |
527 | mentioned limitation. See F<examples/class.pl> (in the CPAN distribution of |
528 | this module) for how to create a class that supports object sharing. |
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529 | |
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530 | Does not support C<splice> on arrays! |
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531 | |
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532 | Taking references to the elements of shared arrays and hashes does not |
533 | autovivify the elements, and neither does slicing a shared array/hash over |
534 | non-existent indices/keys autovivify the elements. |
535 | |
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536 | C<share()> allows you to C<< share($hashref->{key}) >> and |
537 | C<< share($arrayref->[idx]) >> without giving any error message. But the |
538 | C<< $hashref->{key} >> or C<< $arrayref->[idx] >> is B<not> shared, causing |
539 | the error "lock can only be used on shared values" to occur when you attempt |
540 | to C<< lock($hasref->{key}) >> or C<< lock($arrayref->[idx]) >> in another |
541 | thread. |
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542 | |
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543 | Using L<refaddr()|Scalar::Util/"refaddr EXPR">) is unreliable for testing |
544 | whether or not two shared references are equivalent (e.g., when testing for |
545 | circular references). Use L<is_shared()/"is_shared VARIABLE">, instead: |
546 | |
547 | use threads; |
548 | use threads::shared; |
549 | use Scalar::Util qw(refaddr); |
550 | |
551 | # If ref is shared, use threads::shared's internal ID. |
552 | # Otherwise, use refaddr(). |
553 | my $addr1 = is_shared($ref1) || refaddr($ref1); |
554 | my $addr2 = is_shared($ref2) || refaddr($ref2); |
555 | |
556 | if ($addr1 == $addr2) { |
557 | # The refs are equivalent |
558 | } |
559 | |
2e58fc35 |
560 | L<each()|perlfunc/"each HASH"> does not work properly on shared references |
561 | embedded in shared structures. For example: |
562 | |
563 | my %foo :shared; |
564 | $foo{'bar'} = shared_clone({'a'=>'x', 'b'=>'y', 'c'=>'z'}); |
565 | |
566 | while (my ($key, $val) = each(%{$foo{'bar'}})) { |
567 | ... |
568 | } |
569 | |
570 | Either of the following will work instead: |
571 | |
572 | my $ref = $foo{'bar'}; |
573 | while (my ($key, $val) = each(%{$ref})) { |
574 | ... |
575 | } |
576 | |
577 | foreach my $key (keys(%{$foo{'bar'}})) { |
578 | my $val = $foo{'bar'}{$key}; |
579 | ... |
580 | } |
581 | |
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582 | View existing bug reports at, and submit any new bugs, problems, patches, etc. |
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583 | to: L<http://rt.cpan.org/Public/Dist/Display.html?Name=threads-shared> |
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584 | |
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585 | =head1 SEE ALSO |
586 | |
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587 | L<threads::shared> Discussion Forum on CPAN: |
588 | L<http://www.cpanforum.com/dist/threads-shared> |
589 | |
590 | Annotated POD for L<threads::shared>: |
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591 | L<http://annocpan.org/~JDHEDDEN/threads-shared-1.32/shared.pm> |
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592 | |
593 | Source repository: |
594 | L<http://code.google.com/p/threads-shared/> |
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595 | |
596 | L<threads>, L<perlthrtut> |
597 | |
598 | L<http://www.perl.com/pub/a/2002/06/11/threads.html> and |
599 | L<http://www.perl.com/pub/a/2002/09/04/threads.html> |
600 | |
601 | Perl threads mailing list: |
602 | L<http://lists.cpan.org/showlist.cgi?name=iThreads> |
603 | |
604 | =head1 AUTHOR |
605 | |
606 | Artur Bergman E<lt>sky AT crucially DOT netE<gt> |
607 | |
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608 | Documentation borrowed from the old Thread.pm. |
609 | |
610 | CPAN version produced by Jerry D. Hedden E<lt>jdhedden AT cpan DOT orgE<gt>. |
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611 | |
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612 | =head1 LICENSE |
613 | |
614 | threads::shared is released under the same license as Perl. |
615 | |
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616 | =cut |