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| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "Thread 3" |
| 132 | .TH Thread 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" |
| 133 | .SH "NAME" |
| 134 | Thread \- manipulate threads in Perl (for old code only) |
| 135 | .SH "CAVEAT" |
| 136 | .IX Header "CAVEAT" |
| 137 | Perl has two thread models. |
| 138 | .PP |
| 139 | In Perl 5.005 the thread model was that all data is implicitly shared |
| 140 | and shared access to data has to be explicitly synchronized. |
| 141 | This model is called \*(L"5005threads\*(R". |
| 142 | .PP |
| 143 | In Perl 5.6 a new model was introduced in which all is was thread |
| 144 | local and shared access to data has to be explicitly declared. |
| 145 | This model is called \*(L"ithreads\*(R", for \*(L"interpreter threads\*(R". |
| 146 | .PP |
| 147 | In Perl 5.6 the ithreads model was not available as a public \s-1API\s0, |
| 148 | only as an internal \s-1API\s0 that was available for extension writers, |
| 149 | and to implement \fIfork()\fR emulation on Win32 platforms. |
| 150 | .PP |
| 151 | In Perl 5.8 the ithreads model became available through the \f(CW\*(C`threads\*(C'\fR |
| 152 | module. |
| 153 | .PP |
| 154 | Neither model is configured by default into Perl (except, as mentioned |
| 155 | above, in Win32 ithreads are always available.) You can see your |
| 156 | Perl's threading configuration by running \f(CW\*(C`perl \-V\*(C'\fR and looking for |
| 157 | the \fIuse...threads\fR variables, or inside script by \f(CW\*(C`use Config;\*(C'\fR |
| 158 | and testing for \f(CW$Config{use5005threads}\fR and \f(CW$Config{useithreads}\fR. |
| 159 | .PP |
| 160 | For old code and interim backwards compatibility, the Thread module |
| 161 | has been reworked to function as a frontend for both 5005threads and |
| 162 | ithreads. |
| 163 | .PP |
| 164 | Note that the compatibility is not complete: because the data sharing |
| 165 | models are directly opposed, anything to do with data sharing has to |
| 166 | be thought differently. With the ithreads you must explicitly \fIshare()\fR |
| 167 | variables between the threads. |
| 168 | .PP |
| 169 | For new code the use of the \f(CW\*(C`Thread\*(C'\fR module is discouraged and |
| 170 | the direct use of the \f(CW\*(C`threads\*(C'\fR and \f(CW\*(C`threads::shared\*(C'\fR modules |
| 171 | is encouraged instead. |
| 172 | .PP |
| 173 | Finally, note that there are many known serious problems with the |
| 174 | 5005threads, one of the least of which is that regular expression |
| 175 | match variables like \f(CW$1\fR are not threadsafe, that is, they easily get |
| 176 | corrupted by competing threads. Other problems include more insidious |
| 177 | data corruption and mysterious crashes. You are seriously urged to |
| 178 | use ithreads instead. |
| 179 | .SH "SYNOPSIS" |
| 180 | .IX Header "SYNOPSIS" |
| 181 | .Vb 1 |
| 182 | \& use Thread; |
| 183 | .Ve |
| 184 | .PP |
| 185 | .Vb 1 |
| 186 | \& my $t = Thread->new(\e&start_sub, @start_args); |
| 187 | .Ve |
| 188 | .PP |
| 189 | .Vb 3 |
| 190 | \& $result = $t->join; |
| 191 | \& $result = $t->eval; |
| 192 | \& $t->detach; |
| 193 | .Ve |
| 194 | .PP |
| 195 | .Vb 3 |
| 196 | \& if ($t->done) { |
| 197 | \& $t->join; |
| 198 | \& } |
| 199 | .Ve |
| 200 | .PP |
| 201 | .Vb 3 |
| 202 | \& if($t->equal($another_thread)) { |
| 203 | \& # ... |
| 204 | \& } |
| 205 | .Ve |
| 206 | .PP |
| 207 | .Vb 1 |
| 208 | \& yield(); |
| 209 | .Ve |
| 210 | .PP |
| 211 | .Vb 1 |
| 212 | \& my $tid = Thread->self->tid; |
| 213 | .Ve |
| 214 | .PP |
| 215 | .Vb 3 |
| 216 | \& lock($scalar); |
| 217 | \& lock(@array); |
| 218 | \& lock(%hash); |
| 219 | .Ve |
| 220 | .PP |
| 221 | .Vb 1 |
| 222 | \& lock(\e&sub); # not available with ithreads |
| 223 | .Ve |
| 224 | .PP |
| 225 | .Vb 1 |
| 226 | \& $flags = $t->flags; # not available with ithreads |
| 227 | .Ve |
| 228 | .PP |
| 229 | .Vb 1 |
| 230 | \& my @list = Thread->list; # not available with ithreads |
| 231 | .Ve |
| 232 | .PP |
| 233 | .Vb 1 |
| 234 | \& use Thread 'async'; |
| 235 | .Ve |
| 236 | .SH "DESCRIPTION" |
| 237 | .IX Header "DESCRIPTION" |
| 238 | The \f(CW\*(C`Thread\*(C'\fR module provides multithreading support for perl. |
| 239 | .SH "FUNCTIONS" |
| 240 | .IX Header "FUNCTIONS" |
| 241 | .IP "$thread = Thread\->new(\e&start_sub)" 8 |
| 242 | .IX Item "$thread = Thread->new(&start_sub)" |
| 243 | .PD 0 |
| 244 | .IP "$thread = Thread\->new(\e&start_sub, \s-1LIST\s0)" 8 |
| 245 | .IX Item "$thread = Thread->new(&start_sub, LIST)" |
| 246 | .PD |
| 247 | \&\f(CW\*(C`new\*(C'\fR starts a new thread of execution in the referenced subroutine. The |
| 248 | optional list is passed as parameters to the subroutine. Execution |
| 249 | continues in both the subroutine and the code after the \f(CW\*(C`new\*(C'\fR call. |
| 250 | .Sp |
| 251 | \&\f(CW\*(C`Thread\->new\*(C'\fR returns a thread object representing the newly created |
| 252 | thread. |
| 253 | .IP "lock \s-1VARIABLE\s0" 8 |
| 254 | .IX Item "lock VARIABLE" |
| 255 | \&\f(CW\*(C`lock\*(C'\fR places a lock on a variable until the lock goes out of scope. |
| 256 | .Sp |
| 257 | If the variable is locked by another thread, the \f(CW\*(C`lock\*(C'\fR call will |
| 258 | block until it's available. \f(CW\*(C`lock\*(C'\fR is recursive, so multiple calls |
| 259 | to \f(CW\*(C`lock\*(C'\fR are safe\*(--the variable will remain locked until the |
| 260 | outermost lock on the variable goes out of scope. |
| 261 | .Sp |
| 262 | Locks on variables only affect \f(CW\*(C`lock\*(C'\fR calls\*(--they do \fInot\fR affect normal |
| 263 | access to a variable. (Locks on subs are different, and covered in a bit.) |
| 264 | If you really, \fIreally\fR want locks to block access, then go ahead and tie |
| 265 | them to something and manage this yourself. This is done on purpose. |
| 266 | While managing access to variables is a good thing, Perl doesn't force |
| 267 | you out of its living room... |
| 268 | .Sp |
| 269 | If a container object, such as a hash or array, is locked, all the |
| 270 | elements of that container are not locked. For example, if a thread |
| 271 | does a \f(CW\*(C`lock @a\*(C'\fR, any other thread doing a \f(CW\*(C`lock($a[12])\*(C'\fR won't |
| 272 | block. |
| 273 | .Sp |
| 274 | With 5005threads you may also \f(CW\*(C`lock\*(C'\fR a sub, using \f(CW\*(C`lock &sub\*(C'\fR. |
| 275 | Any calls to that sub from another thread will block until the lock |
| 276 | is released. This behaviour is not equivalent to declaring the sub |
| 277 | with the \f(CW\*(C`locked\*(C'\fR attribute. The \f(CW\*(C`locked\*(C'\fR attribute serializes |
| 278 | access to a subroutine, but allows different threads non-simultaneous |
| 279 | access. \f(CW\*(C`lock &sub\*(C'\fR, on the other hand, will not allow \fIany\fR other |
| 280 | thread access for the duration of the lock. |
| 281 | .Sp |
| 282 | Finally, \f(CW\*(C`lock\*(C'\fR will traverse up references exactly \fIone\fR level. |
| 283 | \&\f(CW\*(C`lock(\e$a)\*(C'\fR is equivalent to \f(CW\*(C`lock($a)\*(C'\fR, while \f(CW\*(C`lock(\e\e$a)\*(C'\fR is not. |
| 284 | .IP "async \s-1BLOCK\s0;" 8 |
| 285 | .IX Item "async BLOCK;" |
| 286 | \&\f(CW\*(C`async\*(C'\fR creates a thread to execute the block immediately following |
| 287 | it. This block is treated as an anonymous sub, and so must have a |
| 288 | semi-colon after the closing brace. Like \f(CW\*(C`Thread\->new\*(C'\fR, \f(CW\*(C`async\*(C'\fR |
| 289 | returns a thread object. |
| 290 | .IP "Thread\->self" 8 |
| 291 | .IX Item "Thread->self" |
| 292 | The \f(CW\*(C`Thread\->self\*(C'\fR function returns a thread object that represents |
| 293 | the thread making the \f(CW\*(C`Thread\->self\*(C'\fR call. |
| 294 | .IP "cond_wait \s-1VARIABLE\s0" 8 |
| 295 | .IX Item "cond_wait VARIABLE" |
| 296 | The \f(CW\*(C`cond_wait\*(C'\fR function takes a \fBlocked\fR variable as |
| 297 | a parameter, unlocks the variable, and blocks until another thread |
| 298 | does a \f(CW\*(C`cond_signal\*(C'\fR or \f(CW\*(C`cond_broadcast\*(C'\fR for that same locked |
| 299 | variable. The variable that \f(CW\*(C`cond_wait\*(C'\fR blocked on is relocked |
| 300 | after the \f(CW\*(C`cond_wait\*(C'\fR is satisfied. If there are multiple threads |
| 301 | \&\f(CW\*(C`cond_wait\*(C'\fRing on the same variable, all but one will reblock waiting |
| 302 | to reaquire the lock on the variable. (So if you're only using |
| 303 | \&\f(CW\*(C`cond_wait\*(C'\fR for synchronization, give up the lock as soon as |
| 304 | possible.) |
| 305 | .IP "cond_signal \s-1VARIABLE\s0" 8 |
| 306 | .IX Item "cond_signal VARIABLE" |
| 307 | The \f(CW\*(C`cond_signal\*(C'\fR function takes a locked variable as a parameter and |
| 308 | unblocks one thread that's \f(CW\*(C`cond_wait\*(C'\fRing on that variable. If more than |
| 309 | one thread is blocked in a \f(CW\*(C`cond_wait\*(C'\fR on that variable, only one (and |
| 310 | which one is indeterminate) will be unblocked. |
| 311 | .Sp |
| 312 | If there are no threads blocked in a \f(CW\*(C`cond_wait\*(C'\fR on the variable, |
| 313 | the signal is discarded. |
| 314 | .IP "cond_broadcast \s-1VARIABLE\s0" 8 |
| 315 | .IX Item "cond_broadcast VARIABLE" |
| 316 | The \f(CW\*(C`cond_broadcast\*(C'\fR function works similarly to \f(CW\*(C`cond_signal\*(C'\fR. |
| 317 | \&\f(CW\*(C`cond_broadcast\*(C'\fR, though, will unblock \fBall\fR the threads that are |
| 318 | blocked in a \f(CW\*(C`cond_wait\*(C'\fR on the locked variable, rather than only |
| 319 | one. |
| 320 | .IP "yield" 8 |
| 321 | .IX Item "yield" |
| 322 | The \f(CW\*(C`yield\*(C'\fR function allows another thread to take control of the |
| 323 | \&\s-1CPU\s0. The exact results are implementation\-dependent. |
| 324 | .SH "METHODS" |
| 325 | .IX Header "METHODS" |
| 326 | .IP "join" 8 |
| 327 | .IX Item "join" |
| 328 | \&\f(CW\*(C`join\*(C'\fR waits for a thread to end and returns any values the thread |
| 329 | exited with. \f(CW\*(C`join\*(C'\fR will block until the thread has ended, though |
| 330 | it won't block if the thread has already terminated. |
| 331 | .Sp |
| 332 | If the thread being \f(CW\*(C`join\*(C'\fRed \f(CW\*(C`die\*(C'\fRd, the error it died with will |
| 333 | be returned at this time. If you don't want the thread performing |
| 334 | the \f(CW\*(C`join\*(C'\fR to die as well, you should either wrap the \f(CW\*(C`join\*(C'\fR in |
| 335 | an \f(CW\*(C`eval\*(C'\fR or use the \f(CW\*(C`eval\*(C'\fR thread method instead of \f(CW\*(C`join\*(C'\fR. |
| 336 | .IP "eval" 8 |
| 337 | .IX Item "eval" |
| 338 | The \f(CW\*(C`eval\*(C'\fR method wraps an \f(CW\*(C`eval\*(C'\fR around a \f(CW\*(C`join\*(C'\fR, and so waits for |
| 339 | a thread to exit, passing along any values the thread might have returned. |
| 340 | Errors, of course, get placed into \f(CW$@\fR. (Not available with ithreads.) |
| 341 | .IP "detach" 8 |
| 342 | .IX Item "detach" |
| 343 | \&\f(CW\*(C`detach\*(C'\fR tells a thread that it is never going to be joined i.e. |
| 344 | that all traces of its existence can be removed once it stops running. |
| 345 | Errors in detached threads will not be visible anywhere \- if you want |
| 346 | to catch them, you should use \f(CW$SIG\fR{_\|_DIE_\|_} or something like that. |
| 347 | .IP "equal" 8 |
| 348 | .IX Item "equal" |
| 349 | \&\f(CW\*(C`equal\*(C'\fR tests whether two thread objects represent the same thread and |
| 350 | returns true if they do. |
| 351 | .IP "tid" 8 |
| 352 | .IX Item "tid" |
| 353 | The \f(CW\*(C`tid\*(C'\fR method returns the tid of a thread. The tid is |
| 354 | a monotonically increasing integer assigned when a thread is |
| 355 | created. The main thread of a program will have a tid of zero, |
| 356 | while subsequent threads will have tids assigned starting with one. |
| 357 | .IP "flags" 8 |
| 358 | .IX Item "flags" |
| 359 | The \f(CW\*(C`flags\*(C'\fR method returns the flags for the thread. This is the |
| 360 | integer value corresponding to the internal flags for the thread, |
| 361 | and the value may not be all that meaningful to you. |
| 362 | (Not available with ithreads.) |
| 363 | .IP "done" 8 |
| 364 | .IX Item "done" |
| 365 | The \f(CW\*(C`done\*(C'\fR method returns true if the thread you're checking has |
| 366 | finished, and false otherwise. (Not available with ithreads.) |
| 367 | .SH "LIMITATIONS" |
| 368 | .IX Header "LIMITATIONS" |
| 369 | The sequence number used to assign tids is a simple integer, and no |
| 370 | checking is done to make sure the tid isn't currently in use. If a |
| 371 | program creates more than 2**32 \- 1 threads in a single run, threads |
| 372 | may be assigned duplicate tids. This limitation may be lifted in |
| 373 | a future version of Perl. |
| 374 | .SH "SEE ALSO" |
| 375 | .IX Header "SEE ALSO" |
| 376 | threads::shared (not available with 5005threads) |
| 377 | .PP |
| 378 | attributes, Thread::Queue, Thread::Semaphore, |
| 379 | Thread::Specific (not available with ithreads) |