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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "threads 3" | |
132 | .TH threads 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | threads \- Perl extension allowing use of interpreter based threads from perl | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 1 | |
138 | \& use threads; | |
139 | .Ve | |
140 | .PP | |
141 | .Vb 3 | |
142 | \& sub start_thread { | |
143 | \& print "Thread started\en"; | |
144 | \& } | |
145 | .Ve | |
146 | .PP | |
147 | .Vb 3 | |
148 | \& my $thread = threads->create("start_thread","argument"); | |
149 | \& my $thread2 = $thread->create(sub { print "I am a thread"},"argument"); | |
150 | \& my $thread3 = async { foreach (@files) { ... } }; | |
151 | .Ve | |
152 | .PP | |
153 | .Vb 2 | |
154 | \& $thread->join(); | |
155 | \& $thread->detach(); | |
156 | .Ve | |
157 | .PP | |
158 | .Vb 2 | |
159 | \& $thread = threads->self(); | |
160 | \& $thread = threads->object( $tid ); | |
161 | .Ve | |
162 | .PP | |
163 | .Vb 3 | |
164 | \& $thread->tid(); | |
165 | \& threads->tid(); | |
166 | \& threads->self->tid(); | |
167 | .Ve | |
168 | .PP | |
169 | .Vb 1 | |
170 | \& threads->yield(); | |
171 | .Ve | |
172 | .PP | |
173 | .Vb 1 | |
174 | \& threads->list(); | |
175 | .Ve | |
176 | .SH "DESCRIPTION" | |
177 | .IX Header "DESCRIPTION" | |
178 | Perl 5.6 introduced something called interpreter threads. Interpreter | |
179 | threads are different from \*(L"5005threads\*(R" (the thread model of Perl | |
180 | 5.005) by creating a new perl interpreter per thread and not sharing | |
181 | any data or state between threads by default. | |
182 | .PP | |
183 | Prior to perl 5.8 this has only been available to people embedding | |
184 | perl and for emulating \fIfork()\fR on windows. | |
185 | .PP | |
186 | The threads \s-1API\s0 is loosely based on the old Thread.pm \s-1API\s0. It is very | |
187 | important to note that variables are not shared between threads, all | |
188 | variables are per default thread local. To use shared variables one | |
189 | must use threads::shared. | |
190 | .PP | |
191 | It is also important to note that you must enable threads by doing | |
192 | \&\f(CW\*(C`use threads\*(C'\fR as early as possible in the script itself and that it | |
193 | is not possible to enable threading inside an \f(CW\*(C`eval ""\*(C'\fR, \f(CW\*(C`do\*(C'\fR, | |
194 | \&\f(CW\*(C`require\*(C'\fR, or \f(CW\*(C`use\*(C'\fR. In particular, if you are intending to share | |
195 | variables with threads::shared, you must \f(CW\*(C`use threads\*(C'\fR before you | |
196 | \&\f(CW\*(C`use threads::shared\*(C'\fR and \f(CW\*(C`threads\*(C'\fR will emit a warning if you do | |
197 | it the other way around. | |
198 | .IP "$thread = threads\->create(function, \s-1LIST\s0)" 4 | |
199 | .IX Item "$thread = threads->create(function, LIST)" | |
200 | This will create a new thread with the entry point function and give | |
201 | it \s-1LIST\s0 as parameters. It will return the corresponding threads | |
202 | object, or \f(CW\*(C`undef\*(C'\fR if thread creation failed. The \fInew()\fR method is an | |
203 | alias for \fIcreate()\fR. | |
204 | .IP "$thread\->join" 4 | |
205 | .IX Item "$thread->join" | |
206 | This will wait for the corresponding thread to join. When the thread | |
207 | finishes, \fIjoin()\fR will return the return values of the entry point | |
208 | function. If the thread has been detached, an error will be thrown. | |
209 | .Sp | |
210 | The context (void, scalar or list) of the thread creation is also the | |
211 | context for \fIjoin()\fR. This means that if you intend to return an array | |
212 | from a thread, you must use \f(CW\*(C`my ($thread) = threads\-\*(C'\fRnew(...)>, and | |
213 | that if you intend to return a scalar, you must use \f(CW\*(C`my $thread = ...\*(C'\fR. | |
214 | .Sp | |
215 | If the program exits without all other threads having been either | |
216 | joined or detached, then a warning will be issued. (A program exits | |
217 | either because one of its threads explicitly calls \fIexit()\fR, or in the | |
218 | case of the main thread, reaches the end of the main program file.) | |
219 | .IP "$thread\->detach" 4 | |
220 | .IX Item "$thread->detach" | |
221 | Will make the thread unjoinable, and cause any eventual return value | |
222 | to be discarded. | |
223 | .IP "threads\->self" 4 | |
224 | .IX Item "threads->self" | |
225 | This will return the thread object for the current thread. | |
226 | .IP "$thread\->tid" 4 | |
227 | .IX Item "$thread->tid" | |
228 | This will return the id of the thread. Thread IDs are integers, with | |
229 | the main thread in a program being 0. Currently Perl assigns a unique | |
230 | tid to every thread ever created in your program, assigning the first | |
231 | thread to be created a tid of 1, and increasing the tid by 1 for each | |
232 | new thread that's created. | |
233 | .Sp | |
234 | \&\s-1NB\s0 the class method \f(CW\*(C`threads\->tid()\*(C'\fR is a quick way to get the | |
235 | current thread id if you don't have your thread object handy. | |
236 | .IP "threads\->object( tid )" 4 | |
237 | .IX Item "threads->object( tid )" | |
238 | This will return the thread object for the thread associated with the | |
239 | specified tid. Returns undef if there is no thread associated with the tid | |
240 | or no tid is specified or the specified tid is undef. | |
241 | .IP "threads\->\fIyield()\fR;" 4 | |
242 | .IX Item "threads->yield();" | |
243 | This is a suggestion to the \s-1OS\s0 to let this thread yield \s-1CPU\s0 time to other | |
244 | threads. What actually happens is highly dependent upon the underlying | |
245 | thread implementation. | |
246 | .Sp | |
247 | You may do \f(CW\*(C`use threads qw(yield)\*(C'\fR then use just a bare \f(CW\*(C`yield\*(C'\fR in your | |
248 | code. | |
249 | .IP "threads\->\fIlist()\fR;" 4 | |
250 | .IX Item "threads->list();" | |
251 | This will return a list of all non joined, non detached threads. | |
252 | .IP "async \s-1BLOCK\s0;" 4 | |
253 | .IX Item "async BLOCK;" | |
254 | \&\f(CW\*(C`async\*(C'\fR creates a thread to execute the block immediately following | |
255 | it. This block is treated as an anonymous sub, and so must have a | |
256 | semi-colon after the closing brace. Like \f(CW\*(C`threads\->new\*(C'\fR, \f(CW\*(C`async\*(C'\fR | |
257 | returns a thread object. | |
258 | .SH "WARNINGS" | |
259 | .IX Header "WARNINGS" | |
260 | .ie n .IP "A thread exited while %d other threads were still running" 4 | |
261 | .el .IP "A thread exited while \f(CW%d\fR other threads were still running" 4 | |
262 | .IX Item "A thread exited while %d other threads were still running" | |
263 | A thread (not necessarily the main thread) exited while there were | |
264 | still other threads running. Usually it's a good idea to first collect | |
265 | the return values of the created threads by joining them, and only then | |
266 | exit from the main thread. | |
267 | .SH "TODO" | |
268 | .IX Header "TODO" | |
269 | The current implementation of threads has been an attempt to get | |
270 | a correct threading system working that could be built on, | |
271 | and optimized, in newer versions of perl. | |
272 | .PP | |
273 | Currently the overhead of creating a thread is rather large, | |
274 | also the cost of returning values can be large. These are areas | |
275 | were there most likely will be work done to optimize what data | |
276 | that needs to be cloned. | |
277 | .SH "BUGS" | |
278 | .IX Header "BUGS" | |
279 | .IP "Parent-Child threads." 4 | |
280 | .IX Item "Parent-Child threads." | |
281 | On some platforms it might not be possible to destroy \*(L"parent\*(R" | |
282 | threads while there are still existing child \*(L"threads\*(R". | |
283 | .Sp | |
284 | This will possibly be fixed in later versions of perl. | |
285 | .IP "tid is I32" 4 | |
286 | .IX Item "tid is I32" | |
287 | The thread id is a 32 bit integer, it can potentially overflow. | |
288 | This might be fixed in a later version of perl. | |
289 | .IP "Returning objects" 4 | |
290 | .IX Item "Returning objects" | |
291 | When you return an object the entire stash that the object is blessed | |
292 | as well. This will lead to a large memory usage. The ideal situation | |
293 | would be to detect the original stash if it existed. | |
294 | .IP "Creating threads inside \s-1BEGIN\s0 blocks" 4 | |
295 | .IX Item "Creating threads inside BEGIN blocks" | |
296 | Creating threads inside \s-1BEGIN\s0 blocks (or during the compilation phase | |
297 | in general) does not work. (In Windows, trying to use \fIfork()\fR inside | |
298 | \&\s-1BEGIN\s0 blocks is an equally losing proposition, since it has been | |
299 | implemented in very much the same way as threads.) | |
300 | .IP "\s-1PERL_OLD_SIGNALS\s0 are not threadsafe, will not be." 4 | |
301 | .IX Item "PERL_OLD_SIGNALS are not threadsafe, will not be." | |
302 | If your Perl has been built with \s-1PERL_OLD_SIGNALS\s0 (one has | |
303 | to explicitly add that symbol to ccflags, see \f(CW\*(C`perl \-V\*(C'\fR), | |
304 | signal handling is not threadsafe. | |
305 | .SH "AUTHOR and COPYRIGHT" | |
306 | .IX Header "AUTHOR and COPYRIGHT" | |
307 | Arthur Bergman <sky at nanisky.com> | |
308 | .PP | |
309 | threads is released under the same license as Perl. | |
310 | .PP | |
311 | Thanks to | |
312 | .PP | |
313 | Richard Soderberg <perl at crystalflame.net> | |
314 | Helping me out tons, trying to find reasons for races and other weird bugs! | |
315 | .PP | |
316 | Simon Cozens <simon at brecon.co.uk> | |
317 | Being there to answer zillions of annoying questions | |
318 | .PP | |
319 | Rocco Caputo <troc at netrus.net> | |
320 | .PP | |
321 | Vipul Ved Prakash <mail at vipul.net> | |
322 | Helping with debugging. | |
323 | .PP | |
324 | please join perl\-ithreads@perl.org for more information | |
325 | .SH "SEE ALSO" | |
326 | .IX Header "SEE ALSO" | |
327 | threads::shared, perlthrtut, | |
328 | <http://www.perl.com/pub/a/2002/06/11/threads.html>, | |
329 | perlcall, perlembed, perlguts |