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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 | use strict; |
5 | use warnings; |
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6 | BEGIN { |
7 | require Exporter; |
8 | our @ISA = qw(Exporter); |
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9 | our @EXPORT = qw(share cond_wait cond_timedwait cond_broadcast cond_signal); |
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10 | our $VERSION = '0.94_01'; |
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11 | |
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12 | if ($threads::threads) { |
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13 | *cond_wait = \&cond_wait_enabled; |
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14 | *cond_timedwait = \&cond_timedwait_enabled; |
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15 | *cond_signal = \&cond_signal_enabled; |
16 | *cond_broadcast = \&cond_broadcast_enabled; |
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17 | require XSLoader; |
18 | XSLoader::load('threads::shared',$VERSION); |
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19 | push @EXPORT,'bless'; |
20 | } |
21 | else { |
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22 | |
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23 | # String eval is generally evil, but we don't want these subs to exist at all |
24 | # if threads are loaded successfully. Vivifying them conditionally this way |
25 | # saves on average about 4K of memory per thread. |
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26 | |
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27 | eval <<'EOD'; |
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28 | sub cond_wait (\[$@%];\[$@%]) { undef } |
29 | sub cond_timedwait (\[$@%]$;\[$@%]) { undef } |
30 | sub cond_signal (\[$@%]) { undef } |
31 | sub cond_broadcast (\[$@%]) { undef } |
32 | sub share (\[$@%]) { return $_[0] } |
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33 | EOD |
34 | } |
35 | } |
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36 | |
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37 | $threads::shared::threads_shared = 1; |
38 | |
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39 | sub threads::shared::tie::SPLICE |
40 | { |
41 | die "Splice not implemented for shared arrays"; |
42 | } |
43 | |
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44 | __END__ |
45 | |
46 | =head1 NAME |
47 | |
48 | threads::shared - Perl extension for sharing data structures between threads |
49 | |
50 | =head1 SYNOPSIS |
51 | |
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52 | use threads; |
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53 | use threads::shared; |
54 | |
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55 | my $var : shared; |
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56 | $var = $scalar_value; |
57 | $var = $shared_ref_value; |
58 | $var = &share($simple_unshared_ref_value); |
59 | $var = &share(new Foo); |
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60 | |
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61 | my($scalar, @array, %hash); |
62 | share($scalar); |
63 | share(@array); |
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64 | share(%hash); |
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65 | my $bar = &share([]); |
66 | $hash{bar} = &share({}); |
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67 | |
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68 | { lock(%hash); ... } |
69 | |
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70 | cond_wait($scalar); |
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71 | cond_timedwait($scalar, time() + 30); |
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72 | cond_broadcast(@array); |
73 | cond_signal(%hash); |
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74 | |
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75 | my $lockvar : shared; |
76 | # condition var != lock var |
77 | cond_wait($var, $lockvar); |
78 | cond_timedwait($var, time()+30, $lockvar); |
79 | |
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80 | =head1 DESCRIPTION |
81 | |
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82 | By default, variables are private to each thread, and each newly created |
83 | thread gets a private copy of each existing variable. This module allows |
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84 | you to share variables across different threads (and pseudoforks on Win32). |
85 | It is used together with the threads module. |
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86 | |
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87 | =head1 EXPORT |
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88 | |
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89 | C<share>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>, C<cond_broadcast> |
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90 | |
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91 | Note that if this module is imported when C<threads> has not yet been |
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92 | loaded, then these functions all become no-ops. This makes it possible |
93 | to write modules that will work in both threaded and non-threaded |
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94 | environments. |
95 | |
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96 | =head1 FUNCTIONS |
97 | |
98 | =over 4 |
99 | |
100 | =item share VARIABLE |
101 | |
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102 | C<share> takes a value and marks it as shared. You can share a scalar, |
103 | array, hash, scalar ref, array ref or hash ref. C<share> will return |
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104 | the shared rvalue but always as a reference. |
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105 | |
106 | C<share> will traverse up references exactly I<one> level. |
107 | C<share(\$a)> is equivalent to C<share($a)>, while C<share(\\$a)> is not. |
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108 | This means that you must create nested shared data structures by first |
109 | creating individual shared leaf notes, then adding them to a shared hash |
110 | or array. |
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111 | |
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112 | A variable can also be marked as shared at compile time by using the |
113 | C<shared> attribute: C<my $var : shared>. |
114 | |
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115 | If you want to share a newly created reference unfortunately you |
116 | need to use C<&share([])> and C<&share({})> syntax due to problems |
117 | with Perl's prototyping. |
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118 | |
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119 | The only values that can be assigned to a shared scalar are other scalar |
120 | values, or shared refs, eg |
121 | |
122 | my $var : shared; |
123 | $var = 1; # ok |
124 | $var = &share([]); # ok |
125 | $var = []; # error |
126 | $var = A->new; # error |
127 | $var = &share(A->new); # ok as long as the A object is not nested |
128 | |
129 | Note that it is often not wise to share an object unless the class itself |
130 | has been written to support sharing; for example, an object's destructor |
131 | may get called multiple times, one for each thread's scope exit. |
132 | |
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133 | =item lock VARIABLE |
134 | |
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135 | C<lock> places a lock on a variable until the lock goes out of scope. |
136 | If the variable is locked by another thread, the C<lock> call will |
137 | block until it's available. C<lock> is recursive, so multiple calls |
138 | to C<lock> are safe -- the variable will remain locked until the |
139 | outermost lock on the variable goes out of scope. |
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140 | |
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141 | If a container object, such as a hash or array, is locked, all the |
142 | elements of that container are not locked. For example, if a thread |
143 | does a C<lock @a>, any other thread doing a C<lock($a[12])> won't block. |
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144 | |
145 | C<lock> will traverse up references exactly I<one> level. |
146 | C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not. |
147 | |
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148 | Note that you cannot explicitly unlock a variable; you can only wait |
149 | for the lock to go out of scope. If you need more fine-grained |
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150 | control, see L<Thread::Semaphore>. |
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151 | |
152 | =item cond_wait VARIABLE |
153 | |
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154 | =item cond_wait CONDVAR, LOCKVAR |
155 | |
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156 | The C<cond_wait> function takes a B<locked> variable as a parameter, |
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157 | unlocks the variable, and blocks until another thread does a |
158 | C<cond_signal> or C<cond_broadcast> for that same locked variable. |
159 | The variable that C<cond_wait> blocked on is relocked after the |
160 | C<cond_wait> is satisfied. If there are multiple threads |
161 | C<cond_wait>ing on the same variable, all but one will reblock waiting |
162 | to reacquire the lock on the variable. (So if you're only using |
163 | C<cond_wait> for synchronisation, give up the lock as soon as |
164 | possible). The two actions of unlocking the variable and entering the |
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165 | blocked wait state are atomic, the two actions of exiting from the |
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166 | blocked wait state and relocking the variable are not. |
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167 | |
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168 | In its second form, C<cond_wait> takes a shared, B<unlocked> variable |
169 | followed by a shared, B<locked> variable. The second variable is |
170 | unlocked and thread execution suspended until another thread signals |
171 | the first variable. |
172 | |
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173 | It is important to note that the variable can be notified even if |
174 | no thread C<cond_signal> or C<cond_broadcast> on the variable. |
175 | It is therefore important to check the value of the variable and |
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176 | go back to waiting if the requirement is not fulfilled. For example, |
177 | to pause until a shared counter drops to zero: |
178 | |
179 | { lock($counter); cond_wait($count) until $counter == 0; } |
180 | |
181 | =item cond_timedwait VARIABLE, ABS_TIMEOUT |
182 | |
183 | =item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR |
184 | |
185 | In its two-argument form, C<cond_timedwait> takes a B<locked> variable |
186 | and an absolute timeout as parameters, unlocks the variable, and blocks |
187 | until the timeout is reached or another thread signals the variable. A |
188 | false value is returned if the timeout is reached, and a true value |
189 | otherwise. In either case, the variable is re-locked upon return. |
190 | |
191 | Like C<cond_wait>, this function may take a shared, B<locked> variable |
192 | as an additional parameter; in this case the first parameter is an |
193 | B<unlocked> condition variable protected by a distinct lock variable. |
194 | |
195 | Again like C<cond_wait>, waking up and reacquiring the lock are not |
196 | atomic, and you should always check your desired condition after this |
197 | function returns. Since the timeout is an absolute value, however, it |
198 | does not have to be recalculated with each pass: |
199 | |
200 | lock($var); |
201 | my $abs = time() + 15; |
202 | until ($ok = desired_condition($var)) { |
203 | last if !cond_timedwait($var, $abs); |
204 | } |
205 | # we got it if $ok, otherwise we timed out! |
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206 | |
207 | =item cond_signal VARIABLE |
208 | |
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209 | The C<cond_signal> function takes a B<locked> variable as a parameter |
210 | and unblocks one thread that's C<cond_wait>ing on that variable. If |
211 | more than one thread is blocked in a C<cond_wait> on that variable, |
212 | only one (and which one is indeterminate) will be unblocked. |
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213 | |
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214 | If there are no threads blocked in a C<cond_wait> on the variable, |
215 | the signal is discarded. By always locking before signaling, you can |
216 | (with care), avoid signaling before another thread has entered cond_wait(). |
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217 | |
218 | C<cond_signal> will normally generate a warning if you attempt to use it |
219 | on an unlocked variable. On the rare occasions where doing this may be |
220 | sensible, you can skip the warning with |
221 | |
222 | { no warnings 'threads'; cond_signal($foo) } |
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223 | |
224 | =item cond_broadcast VARIABLE |
225 | |
226 | The C<cond_broadcast> function works similarly to C<cond_signal>. |
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227 | C<cond_broadcast>, though, will unblock B<all> the threads that are |
228 | blocked in a C<cond_wait> on the locked variable, rather than only one. |
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229 | |
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230 | =back |
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231 | |
232 | =head1 NOTES |
233 | |
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234 | threads::shared is designed to disable itself silently if threads are |
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235 | not available. If you want access to threads, you must C<use threads> |
236 | before you C<use threads::shared>. threads will emit a warning if you |
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237 | use it after threads::shared. |
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238 | |
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239 | =head1 BUGS |
240 | |
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241 | C<bless> is not supported on shared references. In the current version, |
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242 | C<bless> will only bless the thread local reference and the blessing |
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243 | will not propagate to the other threads. This is expected to be |
244 | implemented in a future version of Perl. |
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245 | |
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246 | Does not support splice on arrays! |
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247 | |
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248 | Taking references to the elements of shared arrays and hashes does not |
249 | autovivify the elements, and neither does slicing a shared array/hash |
250 | over non-existent indices/keys autovivify the elements. |
251 | |
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252 | share() allows you to C<< share $hashref->{key} >> without giving any error |
253 | message. But the C<< $hashref->{key} >> is B<not> shared, causing the error |
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254 | "locking can only be used on shared values" to occur when you attempt to |
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255 | C<< lock $hasref->{key} >>. |
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256 | |
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257 | =head1 AUTHOR |
258 | |
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259 | Arthur Bergman E<lt>arthur at contiller.seE<gt> |
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260 | |
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261 | threads::shared is released under the same license as Perl |
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262 | |
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263 | Documentation borrowed from the old Thread.pm |
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264 | |
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265 | =head1 SEE ALSO |
266 | |
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267 | L<threads>, L<perlthrtut>, L<http://www.perl.com/pub/a/2002/06/11/threads.html> |
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268 | |
269 | =cut |