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1 | package Thread; |
2 | |
3 | $VERSION = '2.00'; |
4 | |
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5 | use strict; |
6 | |
7 | our $ithreads; |
8 | our $othreads; |
9 | |
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10 | BEGIN { |
11 | use Config; |
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12 | $ithreads = $Config{useithreads}; |
13 | $othreads = $Config{use5005threads}; |
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14 | } |
15 | |
16 | require Exporter; |
17 | use XSLoader (); |
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18 | our($VERSION, @ISA, @EXPORT, @EXPORT_OK); |
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19 | |
20 | @ISA = qw(Exporter); |
21 | |
22 | BEGIN { |
23 | if ($ithreads) { |
24 | @EXPORT = qw(share cond_wait cond_broadcast cond_signal unlock) |
25 | } elsif ($othreads) { |
26 | @EXPORT_OK = qw(cond_signal cond_broadcast cond_wait); |
27 | } |
28 | push @EXPORT_OK, qw(async yield); |
29 | } |
30 | |
31 | =head1 NAME |
32 | |
33 | Thread - manipulate threads in Perl |
34 | |
35 | =head1 CAVEAT |
36 | |
37 | Perl has two thread models. |
38 | |
39 | In Perl 5.005 the thread model was that all data is implicitly shared |
40 | and shared access to data has to be explicitly synchronized. |
41 | This model is called "5005threads". |
42 | |
43 | In Perl 5.6 a new model was introduced in which all is was thread |
44 | local and shared access to data has to be explicitly declared. |
45 | This model is called "ithreads", for "interpreter threads". |
46 | |
47 | In Perl 5.6 the ithreads model was not available as a public API, |
48 | only as an internal API that was available for extension writers, |
49 | and to implement fork() emulation on Win32 platforms. |
50 | |
51 | In Perl 5.8 the ithreads model became available through the C<threads> |
52 | module. |
53 | |
54 | Neither model is configured by default into Perl (except, as mentioned |
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55 | above, in Win32 ithreads are always available.) You can see your |
56 | Perl's threading configuration by running C<perl -V> and looking for |
57 | the I<use...threads> variables, or inside script by C<use Config;> |
58 | and testing for C<$Config{use5005threads}> and C<$Config{useithreads}>. |
59 | |
60 | For old code and interim backwards compatibility, the Thread module |
61 | has been reworked to function as a frontend for both 5005threads and |
62 | ithreads. |
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63 | |
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64 | Note that the compatibility is not complete: because the data sharing |
65 | models are directly opposed, anything to do with data sharing has to |
66 | be thought differently. With the ithreads you must explicitly share() |
67 | variables between the threads. |
68 | |
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69 | For new code the use of the C<Thread> module is discouraged and |
70 | the direct use use of the C<threads> and C<threads::shared> modules |
71 | is encouraged instead. |
72 | |
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73 | Finally, note that there are many known serious problems with the |
74 | 5005threads, one of the least of which is that regular expression |
75 | match variables like $1 are not threadsafe, that is, they easily get |
76 | corrupted by competing threads. Other problems include more insidious |
77 | data corruption and mysterious crashes. You are seriously urged to |
78 | use ithreads instead. |
79 | |
80 | =head1 SYNOPSIS |
81 | |
82 | use Thread; |
83 | |
84 | my $t = Thread->new(\&start_sub, @start_args); |
85 | |
86 | $result = $t->join; |
87 | $result = $t->eval; |
88 | $t->detach; |
89 | |
90 | if ($t->done) { |
91 | $t->join; |
92 | } |
93 | |
94 | if($t->equal($another_thread)) { |
95 | # ... |
96 | } |
97 | |
98 | yield(); |
99 | |
100 | my $tid = Thread->self->tid; |
101 | |
102 | lock($scalar); |
103 | lock(@array); |
104 | lock(%hash); |
105 | |
106 | lock(\&sub); # not available with ithreads |
107 | |
108 | $flags = $t->flags; # not available with ithreads |
109 | |
110 | my @list = Thread->list; # not available with ithreads |
111 | |
112 | unlock(...); # not available with the 5.005 threads |
113 | |
114 | use Thread 'async'; |
115 | |
116 | =head1 DESCRIPTION |
117 | |
118 | The C<Thread> module provides multithreading support for perl. |
119 | |
120 | =head1 FUNCTIONS |
121 | |
122 | =over 8 |
123 | |
124 | =item $thread = Thread->new(\&start_sub) |
125 | |
126 | =item $thread = Thread->new(\&start_sub, LIST) |
127 | |
128 | C<new> starts a new thread of execution in the referenced subroutine. The |
129 | optional list is passed as parameters to the subroutine. Execution |
130 | continues in both the subroutine and the code after the C<new> call. |
131 | |
132 | C<Thread->new> returns a thread object representing the newly created |
133 | thread. |
134 | |
135 | =item lock VARIABLE |
136 | |
137 | C<lock> places a lock on a variable until the lock goes out of scope |
138 | (with ithreads you can also explicitly unlock()). |
139 | |
140 | If the variable is locked by another thread, the C<lock> call will |
141 | block until it's available. C<lock> is recursive, so multiple calls |
142 | to C<lock> are safe--the variable will remain locked until the |
143 | outermost lock on the variable goes out of scope. |
144 | |
145 | Locks on variables only affect C<lock> calls--they do I<not> affect normal |
146 | access to a variable. (Locks on subs are different, and covered in a bit.) |
147 | If you really, I<really> want locks to block access, then go ahead and tie |
148 | them to something and manage this yourself. This is done on purpose. |
149 | While managing access to variables is a good thing, Perl doesn't force |
150 | you out of its living room... |
151 | |
152 | If a container object, such as a hash or array, is locked, all the |
153 | elements of that container are not locked. For example, if a thread |
154 | does a C<lock @a>, any other thread doing a C<lock($a[12])> won't |
155 | block. |
156 | |
157 | With 5005threads you may also C<lock> a sub, using C<lock &sub>. |
158 | Any calls to that sub from another thread will block until the lock |
159 | is released. This behaviour is not equivalent to declaring the sub |
160 | with the C<locked> attribute. The C<locked> attribute serializes |
161 | access to a subroutine, but allows different threads non-simultaneous |
162 | access. C<lock &sub>, on the other hand, will not allow I<any> other |
163 | thread access for the duration of the lock. |
164 | |
165 | Finally, C<lock> will traverse up references exactly I<one> level. |
166 | C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not. |
167 | |
168 | =item async BLOCK; |
169 | |
170 | C<async> creates a thread to execute the block immediately following |
171 | it. This block is treated as an anonymous sub, and so must have a |
172 | semi-colon after the closing brace. Like C<Thread->new>, C<async> |
173 | returns a thread object. |
174 | |
175 | =item Thread->self |
176 | |
177 | The C<Thread-E<gt>self> function returns a thread object that represents |
178 | the thread making the C<Thread-E<gt>self> call. |
179 | |
180 | =item cond_wait VARIABLE |
181 | |
182 | The C<cond_wait> function takes a B<locked> variable as |
183 | a parameter, unlocks the variable, and blocks until another thread |
184 | does a C<cond_signal> or C<cond_broadcast> for that same locked |
185 | variable. The variable that C<cond_wait> blocked on is relocked |
186 | after the C<cond_wait> is satisfied. If there are multiple threads |
187 | C<cond_wait>ing on the same variable, all but one will reblock waiting |
188 | to reaquire the lock on the variable. (So if you're only using |
189 | C<cond_wait> for synchronization, give up the lock as soon as |
190 | possible.) |
191 | |
192 | =item cond_signal VARIABLE |
193 | |
194 | The C<cond_signal> function takes a locked variable as a parameter and |
195 | unblocks one thread that's C<cond_wait>ing on that variable. If more than |
196 | one thread is blocked in a C<cond_wait> on that variable, only one (and |
197 | which one is indeterminate) will be unblocked. |
198 | |
199 | If there are no threads blocked in a C<cond_wait> on the variable, |
200 | the signal is discarded. |
201 | |
202 | =item cond_broadcast VARIABLE |
203 | |
204 | The C<cond_broadcast> function works similarly to C<cond_signal>. |
205 | C<cond_broadcast>, though, will unblock B<all> the threads that are |
206 | blocked in a C<cond_wait> on the locked variable, rather than only |
207 | one. |
208 | |
209 | =item yield |
210 | |
211 | The C<yield> function allows another thread to take control of the |
212 | CPU. The exact results are implementation-dependent. |
213 | |
214 | =back |
215 | |
216 | =head1 METHODS |
217 | |
218 | =over 8 |
219 | |
220 | =item join |
221 | |
222 | C<join> waits for a thread to end and returns any values the thread |
223 | exited with. C<join> will block until the thread has ended, though |
224 | it won't block if the thread has already terminated. |
225 | |
226 | If the thread being C<join>ed C<die>d, the error it died with will |
227 | be returned at this time. If you don't want the thread performing |
228 | the C<join> to die as well, you should either wrap the C<join> in |
229 | an C<eval> or use the C<eval> thread method instead of C<join>. |
230 | |
231 | =item eval |
232 | |
233 | The C<eval> method wraps an C<eval> around a C<join>, and so waits for |
234 | a thread to exit, passing along any values the thread might have returned. |
235 | Errors, of course, get placed into C<$@>. (Not available with ithreads.) |
236 | |
237 | =item detach |
238 | |
239 | C<detach> tells a thread that it is never going to be joined i.e. |
240 | that all traces of its existence can be removed once it stops running. |
241 | Errors in detached threads will not be visible anywhere - if you want |
242 | to catch them, you should use $SIG{__DIE__} or something like that. |
243 | |
244 | =item equal |
245 | |
246 | C<equal> tests whether two thread objects represent the same thread and |
247 | returns true if they do. |
248 | |
249 | =item tid |
250 | |
251 | The C<tid> method returns the tid of a thread. The tid is |
252 | a monotonically increasing integer assigned when a thread is |
253 | created. The main thread of a program will have a tid of zero, |
254 | while subsequent threads will have tids assigned starting with one. |
255 | |
256 | =item flags |
257 | |
258 | The C<flags> method returns the flags for the thread. This is the |
259 | integer value corresponding to the internal flags for the thread, |
260 | and the value may not be all that meaningful to you. |
261 | (Not available with ithreads.) |
262 | |
263 | =item done |
264 | |
265 | The C<done> method returns true if the thread you're checking has |
266 | finished, and false otherwise. (Not available with ithreads.) |
267 | |
268 | =back |
269 | |
270 | =head1 LIMITATIONS |
271 | |
272 | The sequence number used to assign tids is a simple integer, and no |
273 | checking is done to make sure the tid isn't currently in use. If a |
274 | program creates more than 2**32 - 1 threads in a single run, threads |
275 | may be assigned duplicate tids. This limitation may be lifted in |
276 | a future version of Perl. |
277 | |
278 | =head1 SEE ALSO |
279 | |
280 | L<threads::shared> (not available with 5005threads) |
281 | |
282 | L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>, |
283 | L<Thread::Specific> (not available with ithreads) |
284 | |
285 | =cut |
286 | |
287 | # |
288 | # Methods |
289 | # |
290 | |
291 | # |
292 | # Exported functions |
293 | # |
294 | |
295 | sub async (&) { |
296 | return Thread->new($_[0]); |
297 | } |
298 | |
299 | sub eval { |
300 | return eval { shift->join; }; |
301 | } |
302 | |
303 | sub unimplemented { |
304 | print $_[0], " unimplemented with ", |
305 | $Config{useithreads} ? "ithreads" : "5005threads", "\n"; |
306 | |
307 | } |
308 | |
309 | sub unimplement { |
310 | for my $m (@_) { |
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311 | no strict 'refs'; |
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312 | *{"Thread::$m"} = sub { unimplemented $m }; |
313 | } |
314 | } |
315 | |
316 | BEGIN { |
317 | if ($ithreads) { |
318 | XSLoader::load 'threads'; |
319 | for my $m (qw(new join detach yield self tid equal)) { |
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320 | no strict 'refs'; |
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321 | *{"Thread::$m"} = \&{"threads::$m"}; |
322 | } |
323 | XSLoader::load 'threads::shared'; |
324 | for my $m (qw(cond_signal cond_broadcast cond_wait unlock share)) { |
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325 | no strict 'refs'; |
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326 | *{"Thread::$m"} = \&{"threads::shared::${m}_enabled"}; |
327 | } |
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328 | # trying to unimplement eval gives redefined warning |
329 | unimplement(qw(list done flags)); |
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330 | } elsif ($othreads) { |
331 | XSLoader::load 'Thread'; |
332 | unimplement(qw(unlock)); |
333 | } else { |
334 | require Carp; |
335 | Carp::croak("This Perl has neither ithreads not 5005threads"); |
336 | } |
337 | } |
338 | |
339 | 1; |