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43d3ddbe JH |
1 | package Thread; |
2 | ||
4038bebf JH |
3 | use strict; |
4 | ||
4cf4ea45 | 5 | our($VERSION, $ithreads, $othreads); |
4038bebf | 6 | |
43d3ddbe | 7 | BEGIN { |
4cf4ea45 | 8 | $VERSION = '2.00'; |
43d3ddbe | 9 | use Config; |
4038bebf JH |
10 | $ithreads = $Config{useithreads}; |
11 | $othreads = $Config{use5005threads}; | |
43d3ddbe JH |
12 | } |
13 | ||
14 | require Exporter; | |
15 | use XSLoader (); | |
4cf4ea45 | 16 | our(@ISA, @EXPORT, @EXPORT_OK); |
43d3ddbe JH |
17 | |
18 | @ISA = qw(Exporter); | |
19 | ||
20 | BEGIN { | |
21 | if ($ithreads) { | |
e7b4e24c | 22 | @EXPORT = qw(cond_wait cond_broadcast cond_signal unlock) |
43d3ddbe JH |
23 | } elsif ($othreads) { |
24 | @EXPORT_OK = qw(cond_signal cond_broadcast cond_wait); | |
25 | } | |
26 | push @EXPORT_OK, qw(async yield); | |
27 | } | |
28 | ||
29 | =head1 NAME | |
30 | ||
31 | Thread - manipulate threads in Perl | |
32 | ||
33 | =head1 CAVEAT | |
34 | ||
35 | Perl has two thread models. | |
36 | ||
37 | In Perl 5.005 the thread model was that all data is implicitly shared | |
38 | and shared access to data has to be explicitly synchronized. | |
39 | This model is called "5005threads". | |
40 | ||
41 | In Perl 5.6 a new model was introduced in which all is was thread | |
42 | local and shared access to data has to be explicitly declared. | |
43 | This model is called "ithreads", for "interpreter threads". | |
44 | ||
45 | In Perl 5.6 the ithreads model was not available as a public API, | |
46 | only as an internal API that was available for extension writers, | |
47 | and to implement fork() emulation on Win32 platforms. | |
48 | ||
49 | In Perl 5.8 the ithreads model became available through the C<threads> | |
50 | module. | |
51 | ||
52 | Neither model is configured by default into Perl (except, as mentioned | |
8a20485c JH |
53 | above, in Win32 ithreads are always available.) You can see your |
54 | Perl's threading configuration by running C<perl -V> and looking for | |
55 | the I<use...threads> variables, or inside script by C<use Config;> | |
56 | and testing for C<$Config{use5005threads}> and C<$Config{useithreads}>. | |
57 | ||
58 | For old code and interim backwards compatibility, the Thread module | |
59 | has been reworked to function as a frontend for both 5005threads and | |
60 | ithreads. | |
43d3ddbe | 61 | |
43d3ddbe JH |
62 | Note that the compatibility is not complete: because the data sharing |
63 | models are directly opposed, anything to do with data sharing has to | |
64 | be thought differently. With the ithreads you must explicitly share() | |
65 | variables between the threads. | |
66 | ||
8a20485c JH |
67 | For new code the use of the C<Thread> module is discouraged and |
68 | the direct use use of the C<threads> and C<threads::shared> modules | |
69 | is encouraged instead. | |
70 | ||
43d3ddbe JH |
71 | Finally, note that there are many known serious problems with the |
72 | 5005threads, one of the least of which is that regular expression | |
73 | match variables like $1 are not threadsafe, that is, they easily get | |
74 | corrupted by competing threads. Other problems include more insidious | |
75 | data corruption and mysterious crashes. You are seriously urged to | |
76 | use ithreads instead. | |
77 | ||
78 | =head1 SYNOPSIS | |
79 | ||
80 | use Thread; | |
81 | ||
82 | my $t = Thread->new(\&start_sub, @start_args); | |
83 | ||
84 | $result = $t->join; | |
85 | $result = $t->eval; | |
86 | $t->detach; | |
87 | ||
88 | if ($t->done) { | |
89 | $t->join; | |
90 | } | |
91 | ||
92 | if($t->equal($another_thread)) { | |
93 | # ... | |
94 | } | |
95 | ||
96 | yield(); | |
97 | ||
98 | my $tid = Thread->self->tid; | |
99 | ||
100 | lock($scalar); | |
101 | lock(@array); | |
102 | lock(%hash); | |
103 | ||
104 | lock(\&sub); # not available with ithreads | |
105 | ||
106 | $flags = $t->flags; # not available with ithreads | |
107 | ||
108 | my @list = Thread->list; # not available with ithreads | |
109 | ||
110 | unlock(...); # not available with the 5.005 threads | |
111 | ||
112 | use Thread 'async'; | |
113 | ||
114 | =head1 DESCRIPTION | |
115 | ||
116 | The C<Thread> module provides multithreading support for perl. | |
117 | ||
118 | =head1 FUNCTIONS | |
119 | ||
120 | =over 8 | |
121 | ||
122 | =item $thread = Thread->new(\&start_sub) | |
123 | ||
124 | =item $thread = Thread->new(\&start_sub, LIST) | |
125 | ||
126 | C<new> starts a new thread of execution in the referenced subroutine. The | |
127 | optional list is passed as parameters to the subroutine. Execution | |
128 | continues in both the subroutine and the code after the C<new> call. | |
129 | ||
130 | C<Thread->new> returns a thread object representing the newly created | |
131 | thread. | |
132 | ||
133 | =item lock VARIABLE | |
134 | ||
135 | C<lock> places a lock on a variable until the lock goes out of scope | |
136 | (with ithreads you can also explicitly unlock()). | |
137 | ||
138 | If the variable is locked by another thread, the C<lock> call will | |
139 | block until it's available. C<lock> is recursive, so multiple calls | |
140 | to C<lock> are safe--the variable will remain locked until the | |
141 | outermost lock on the variable goes out of scope. | |
142 | ||
143 | Locks on variables only affect C<lock> calls--they do I<not> affect normal | |
144 | access to a variable. (Locks on subs are different, and covered in a bit.) | |
145 | If you really, I<really> want locks to block access, then go ahead and tie | |
146 | them to something and manage this yourself. This is done on purpose. | |
147 | While managing access to variables is a good thing, Perl doesn't force | |
148 | you out of its living room... | |
149 | ||
150 | If a container object, such as a hash or array, is locked, all the | |
151 | elements of that container are not locked. For example, if a thread | |
152 | does a C<lock @a>, any other thread doing a C<lock($a[12])> won't | |
153 | block. | |
154 | ||
155 | With 5005threads you may also C<lock> a sub, using C<lock &sub>. | |
156 | Any calls to that sub from another thread will block until the lock | |
157 | is released. This behaviour is not equivalent to declaring the sub | |
158 | with the C<locked> attribute. The C<locked> attribute serializes | |
159 | access to a subroutine, but allows different threads non-simultaneous | |
160 | access. C<lock &sub>, on the other hand, will not allow I<any> other | |
161 | thread access for the duration of the lock. | |
162 | ||
163 | Finally, C<lock> will traverse up references exactly I<one> level. | |
164 | C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not. | |
165 | ||
166 | =item async BLOCK; | |
167 | ||
168 | C<async> creates a thread to execute the block immediately following | |
169 | it. This block is treated as an anonymous sub, and so must have a | |
170 | semi-colon after the closing brace. Like C<Thread->new>, C<async> | |
171 | returns a thread object. | |
172 | ||
173 | =item Thread->self | |
174 | ||
175 | The C<Thread-E<gt>self> function returns a thread object that represents | |
176 | the thread making the C<Thread-E<gt>self> call. | |
177 | ||
178 | =item cond_wait VARIABLE | |
179 | ||
180 | The C<cond_wait> function takes a B<locked> variable as | |
181 | a parameter, unlocks the variable, and blocks until another thread | |
182 | does a C<cond_signal> or C<cond_broadcast> for that same locked | |
183 | variable. The variable that C<cond_wait> blocked on is relocked | |
184 | after the C<cond_wait> is satisfied. If there are multiple threads | |
185 | C<cond_wait>ing on the same variable, all but one will reblock waiting | |
186 | to reaquire the lock on the variable. (So if you're only using | |
187 | C<cond_wait> for synchronization, give up the lock as soon as | |
188 | possible.) | |
189 | ||
190 | =item cond_signal VARIABLE | |
191 | ||
192 | The C<cond_signal> function takes a locked variable as a parameter and | |
193 | unblocks one thread that's C<cond_wait>ing on that variable. If more than | |
194 | one thread is blocked in a C<cond_wait> on that variable, only one (and | |
195 | which one is indeterminate) will be unblocked. | |
196 | ||
197 | If there are no threads blocked in a C<cond_wait> on the variable, | |
198 | the signal is discarded. | |
199 | ||
200 | =item cond_broadcast VARIABLE | |
201 | ||
202 | The C<cond_broadcast> function works similarly to C<cond_signal>. | |
203 | C<cond_broadcast>, though, will unblock B<all> the threads that are | |
204 | blocked in a C<cond_wait> on the locked variable, rather than only | |
205 | one. | |
206 | ||
207 | =item yield | |
208 | ||
209 | The C<yield> function allows another thread to take control of the | |
210 | CPU. The exact results are implementation-dependent. | |
211 | ||
212 | =back | |
213 | ||
214 | =head1 METHODS | |
215 | ||
216 | =over 8 | |
217 | ||
218 | =item join | |
219 | ||
220 | C<join> waits for a thread to end and returns any values the thread | |
221 | exited with. C<join> will block until the thread has ended, though | |
222 | it won't block if the thread has already terminated. | |
223 | ||
224 | If the thread being C<join>ed C<die>d, the error it died with will | |
225 | be returned at this time. If you don't want the thread performing | |
226 | the C<join> to die as well, you should either wrap the C<join> in | |
227 | an C<eval> or use the C<eval> thread method instead of C<join>. | |
228 | ||
229 | =item eval | |
230 | ||
231 | The C<eval> method wraps an C<eval> around a C<join>, and so waits for | |
232 | a thread to exit, passing along any values the thread might have returned. | |
233 | Errors, of course, get placed into C<$@>. (Not available with ithreads.) | |
234 | ||
235 | =item detach | |
236 | ||
237 | C<detach> tells a thread that it is never going to be joined i.e. | |
238 | that all traces of its existence can be removed once it stops running. | |
239 | Errors in detached threads will not be visible anywhere - if you want | |
240 | to catch them, you should use $SIG{__DIE__} or something like that. | |
241 | ||
242 | =item equal | |
243 | ||
244 | C<equal> tests whether two thread objects represent the same thread and | |
245 | returns true if they do. | |
246 | ||
247 | =item tid | |
248 | ||
249 | The C<tid> method returns the tid of a thread. The tid is | |
250 | a monotonically increasing integer assigned when a thread is | |
251 | created. The main thread of a program will have a tid of zero, | |
252 | while subsequent threads will have tids assigned starting with one. | |
253 | ||
254 | =item flags | |
255 | ||
256 | The C<flags> method returns the flags for the thread. This is the | |
257 | integer value corresponding to the internal flags for the thread, | |
258 | and the value may not be all that meaningful to you. | |
259 | (Not available with ithreads.) | |
260 | ||
261 | =item done | |
262 | ||
263 | The C<done> method returns true if the thread you're checking has | |
264 | finished, and false otherwise. (Not available with ithreads.) | |
265 | ||
266 | =back | |
267 | ||
268 | =head1 LIMITATIONS | |
269 | ||
270 | The sequence number used to assign tids is a simple integer, and no | |
271 | checking is done to make sure the tid isn't currently in use. If a | |
272 | program creates more than 2**32 - 1 threads in a single run, threads | |
273 | may be assigned duplicate tids. This limitation may be lifted in | |
274 | a future version of Perl. | |
275 | ||
276 | =head1 SEE ALSO | |
277 | ||
278 | L<threads::shared> (not available with 5005threads) | |
279 | ||
280 | L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>, | |
281 | L<Thread::Specific> (not available with ithreads) | |
282 | ||
283 | =cut | |
284 | ||
285 | # | |
286 | # Methods | |
287 | # | |
288 | ||
289 | # | |
290 | # Exported functions | |
291 | # | |
292 | ||
293 | sub async (&) { | |
294 | return Thread->new($_[0]); | |
295 | } | |
296 | ||
297 | sub eval { | |
298 | return eval { shift->join; }; | |
299 | } | |
300 | ||
301 | sub unimplemented { | |
302 | print $_[0], " unimplemented with ", | |
303 | $Config{useithreads} ? "ithreads" : "5005threads", "\n"; | |
304 | ||
305 | } | |
306 | ||
307 | sub unimplement { | |
308 | for my $m (@_) { | |
4038bebf | 309 | no strict 'refs'; |
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310 | *{"Thread::$m"} = sub { unimplemented $m }; |
311 | } | |
312 | } | |
313 | ||
314 | BEGIN { | |
315 | if ($ithreads) { | |
733129fe JH |
316 | if ($othreads) { |
317 | require Carp; | |
318 | Carp::croak("This Perl has both ithreads and 5005threads (serious malconfiguration)"); | |
319 | } | |
43d3ddbe | 320 | XSLoader::load 'threads'; |
e7b4e24c | 321 | for my $m (qw(new join detach yield self tid equal list)) { |
4038bebf | 322 | no strict 'refs'; |
43d3ddbe JH |
323 | *{"Thread::$m"} = \&{"threads::$m"}; |
324 | } | |
e7b4e24c AB |
325 | require 'threads/shared.pm'; |
326 | for my $m (qw(cond_signal cond_broadcast cond_wait unlock)) { | |
4038bebf | 327 | no strict 'refs'; |
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328 | *{"Thread::$m"} = \&{"threads::shared::${m}_enabled"}; |
329 | } | |
d7ceb7fc | 330 | # trying to unimplement eval gives redefined warning |
e7b4e24c | 331 | unimplement(qw(done flags)); |
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332 | } elsif ($othreads) { |
333 | XSLoader::load 'Thread'; | |
334 | unimplement(qw(unlock)); | |
335 | } else { | |
336 | require Carp; | |
733129fe | 337 | Carp::croak("This Perl has neither ithreads nor 5005threads"); |
43d3ddbe JH |
338 | } |
339 | } | |
340 | ||
341 | 1; |