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1 | NOTE |
2 | ||
3 | Threading is a highly experimental feature. There are still a | |
4 | few race conditions that show up under high contention on SMP | |
5 | machines. Internal implementation is still subject to changes. | |
6 | It is not recommended for production use at this time. | |
7 | ||
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8 | Building |
9 | ||
d81a1b93 | 10 | If you want to build with multi-threading support and you are |
69ce17de | 11 | running one of the following: |
e2198c6b | 12 | |
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13 | * Linux 2.x (with the LinuxThreads library installed: that's |
14 | the linuxthreads and linuxthreads-devel RPMs for RedHat) | |
15 | ||
16 | * Digital UNIX 4.x | |
17 | ||
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18 | * Digital UNIX 3.x (Formerly DEC OSF/1), see additional note below |
19 | ||
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20 | * Solaris 2.x for recentish x (2.5 is OK) |
21 | ||
22 | * IRIX 6.2 or newer. 6.2 will require a few os patches. | |
23 | IMPORTANT: Without patch 2401, a kernel bug in IRIX 6.2 will | |
24 | cause your machine to panic and crash when running threaded perl. | |
25 | IRIX 6.3 and up should be OK. See lower down for patch details. | |
26 | ||
d81a1b93 | 27 | then you should be able to use |
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28 | |
29 | ./Configure -Dusethreads -des | |
d81a1b93 | 30 | make |
e2198c6b | 31 | |
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32 | and ignore the rest of this "Building" section. If it doesn't |
33 | work or you are using another platform which you believe supports | |
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34 | POSIX.1c threads then read on. Additional information may be in |
35 | a platform-specific "hints" file in the hints/ subdirectory. | |
36 | ||
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37 | On other platforms that use Configure to build perl, omit the -d |
38 | from your ./Configure arguments. For example, use: | |
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39 | |
40 | ./Configure -Dusethreads | |
41 | ||
42 | When Configure prompts you for ccflags, insert any other arguments in | |
43 | there that your compiler needs to use POSIX threads. When Configure | |
44 | prompts you for linking flags, include any flags required for | |
45 | threading (usually nothing special is required here). Finally, when | |
46 | COnfigure prompts you for libraries, include any necessary libraries | |
47 | (e.g. -lpthread). Pay attention to the order of libraries. It is | |
48 | probably necessary to specify your threading library *before* your | |
49 | standard C library, e.g. it might be necessary to have -lpthread -lc, | |
50 | instead of -lc -lpthread. | |
51 | ||
52 | Once you have specified all your compiler flags, you can have Configure | |
53 | accept all the defaults for the remainder of the session by typing &-d | |
54 | at any Configure prompt. | |
55 | ||
56 | Some additional notes (some of these may be obsolete now, other items | |
57 | may be handled automatically): | |
58 | ||
72aaf631 | 59 | For Digital Unix 4.x: |
e2198c6b | 60 | Add -pthread to ccflags |
72aaf631 | 61 | Add -pthread to ldflags |
d81a1b93 | 62 | Add -lpthread -lc_r to lddlflags |
e2198c6b | 63 | |
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64 | For some reason, the extra includes for pthreads make Digital UNIX |
65 | complain fatally about the sbrk() delcaration in perl's malloc.c | |
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66 | so use the native malloc, e.g. sh Configure -Uusemymalloc, or |
67 | manually edit your config.sh as follows: | |
68 | Change usemymalloc to n | |
69 | Zap mallocobj and mallocsrc (foo='') | |
70 | Change d_mymalloc to undef | |
71 | ||
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72 | For Digital Unix 3.x (Formerly DEC OSF/1): |
73 | Add -DOLD_PTHREADS_API to ccflags | |
74 | If compiling with the GNU cc compiler, remove -thread from ccflags | |
75 | ||
76 | (The following should be done automatically if you call Configure | |
77 | with the -Dusethreads option). | |
78 | Add -lpthread -lmach -lc_r to libs (in the order specified). | |
79 | ||
eb1cfdd6 | 80 | For IRIX: |
e2198c6b | 81 | (This should all be done automatically by the hint file). |
eb1cfdd6 | 82 | Add -lpthread to libs |
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83 | For IRIX 6.2, you have to have the following patches installed: |
84 | 1404 Irix 6.2 Posix 1003.1b man pages | |
85 | 1645 IRIX 6.2 & 6.3 POSIX header file updates | |
86 | 2000 Irix 6.2 Posix 1003.1b support modules | |
87 | 2254 Pthread library fixes | |
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88 | 2401 6.2 all platform kernel rollup |
89 | IMPORTANT: Without patch 2401, a kernel bug in IRIX 6.2 will | |
90 | cause your machine to panic and crash when running threaded perl. | |
91 | IRIX 6.3 and up should be OK. | |
92 | ||
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93 | For IRIX 6.3 and 6.4 the pthreads should work out of the box. |
94 | Thanks to Hannu Napari <Hannu.Napari@hut.fi> for the IRIX | |
95 | pthreads patches information. | |
ce637636 | 96 | For AIX: |
e2198c6b | 97 | (This should all be done automatically by the hint file). |
ce637636 | 98 | Change cc to xlc_r or cc_r. |
e2198c6b | 99 | Add -DNEED_PTHREAD_INIT to ccflags and cppflags |
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100 | Add -lc_r to libswanted |
101 | Change -lc in lddflags to be -lpthread -lc_r -lc | |
72aaf631 | 102 | |
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103 | For Win32: |
104 | See README.win32, and the notes at the beginning of win32/Makefile | |
105 | or win32/makefile.mk. | |
106 | ||
72aaf631 | 107 | Now you can do a |
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108 | make |
109 | ||
72aaf631 | 110 | |
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111 | O/S specific bugs |
112 | ||
e2198c6b | 113 | Irix 6.2: See the Irix warning above. |
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114 | |
115 | LinuxThreads 0.5 has a bug which can cause file descriptor 0 to be | |
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116 | closed after a fork() leading to many strange symptoms. Version 0.6 |
117 | has this fixed but the following patch can be applied to 0.5 for now: | |
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118 | |
119 | ----------------------------- cut here ----------------------------- | |
120 | --- linuxthreads-0.5/pthread.c.ORI Mon Oct 6 13:55:50 1997 | |
121 | +++ linuxthreads-0.5/pthread.c Mon Oct 6 13:57:24 1997 | |
122 | @@ -312,8 +312,10 @@ | |
123 | free(pthread_manager_thread_bos); | |
124 | pthread_manager_thread_bos = pthread_manager_thread_tos = NULL; | |
125 | /* Close the two ends of the pipe */ | |
126 | - close(pthread_manager_request); | |
127 | - close(pthread_manager_reader); | |
128 | + if (pthread_manager_request >= 0) { | |
129 | + close(pthread_manager_request); | |
130 | + close(pthread_manager_reader); | |
131 | + } | |
132 | pthread_manager_request = pthread_manager_reader = -1; | |
133 | /* Update the pid of the main thread */ | |
134 | self->p_pid = getpid(); | |
135 | ----------------------------- cut here ----------------------------- | |
136 | ||
137 | ||
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138 | Building the Thread extension |
139 | ||
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140 | The Thread extension is now part of the main perl distribution tree. |
141 | If you did Configure -Dusethreads then it will have been added to | |
142 | the list of extensions automatically. | |
72aaf631 | 143 | |
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144 | You can try some of the tests with |
145 | cd ext/Thread | |
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146 | perl create.t |
147 | perl join.t | |
148 | perl lock.t | |
149 | perl io.t | |
150 | etc. | |
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151 | The io one leaves a thread reading from the keyboard on stdin so |
152 | as the ping messages appear you can type lines and see them echoed. | |
153 | ||
154 | Try running the main perl test suite too. There are known | |
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155 | failures for some of the DBM/DB extensions (if their underlying |
156 | libraries were not compiled to be thread-aware). | |
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157 | |
158 | ||
159 | Bugs | |
160 | ||
72aaf631 | 161 | * FAKE_THREADS should produce a working perl but the Thread |
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162 | extension won't build with it yet. (FAKE_THREADS has not been |
163 | tested at all in recent times.) | |
72aaf631 | 164 | |
5756a3ac | 165 | * There may still be races where bugs show up under contention. |
72aaf631 | 166 | |
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167 | * Need to document "lock", Thread.pm, Queue.pm, ... |
168 | ||
72aaf631 | 169 | |
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170 | Debugging |
171 | ||
8b73bbec | 172 | Use the -DS command-line option to turn on debugging of the |
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173 | multi-threading code. Under Linux, that also turns on a quick |
174 | hack I did to grab a bit of extra information from segfaults. | |
175 | If you have a fancier gdb/threads setup than I do then you'll | |
176 | have to delete the lines in perl.c which say | |
177 | #if defined(DEBUGGING) && defined(USE_THREADS) && defined(__linux__) | |
8b73bbec | 178 | DEBUG_S(signal(SIGSEGV, (void(*)(int))catch_sigsegv);); |
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179 | #endif |
180 | ||
181 | ||
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182 | Background |
183 | ||
184 | Some old globals (e.g. stack_sp, op) and some old per-interpreter | |
185 | variables (e.g. tmps_stack, cxstack) move into struct thread. | |
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186 | All fields of struct thread which derived from original perl |
187 | variables have names of the form Tfoo. For example, stack_sp becomes | |
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188 | the field Tstack_sp of struct thread. For those fields which moved |
189 | from original perl, thread.h does | |
190 | #define foo (thr->Tfoo) | |
191 | This means that all functions in perl which need to use one of these | |
192 | fields need an (automatic) variable thr which points at the current | |
193 | thread's struct thread. For pp_foo functions, it is passed around as | |
194 | an argument, for other functions they do | |
195 | dTHR; | |
196 | which declares and initialises thr from thread-specific data | |
197 | via pthread_getspecific. If a function fails to compile with an | |
198 | error about "no such variable thr", it probably just needs a dTHR | |
199 | at the top. | |
200 | ||
201 | ||
202 | Fake threads | |
203 | ||
204 | For FAKE_THREADS, thr is a global variable and perl schedules threads | |
205 | by altering thr in between appropriate ops. The next and prev fields | |
206 | of struct thread keep all fake threads on a doubly linked list and | |
207 | the next_run and prev_run fields keep all runnable threads on a | |
208 | doubly linked list. Mutexes are stubs for FAKE_THREADS. Condition | |
209 | variables are implemented as a list of waiting threads. | |
210 | ||
211 | ||
212 | Mutexes and condition variables | |
213 | ||
214 | The API is via macros MUTEX_{INIT,LOCK,UNLOCK,DESTROY} and | |
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215 | COND_{INIT,WAIT,SIGNAL,BROADCAST,DESTROY}. |
216 | ||
217 | A mutex is only required to be a simple, fast mutex (e.g. it does not | |
218 | have to be recursive). It is only ever held across very short pieces | |
219 | of code. Condition variables are only ever signalled/broadcast while | |
220 | their associated mutex is held. (This constraint simplifies the | |
221 | implementation of condition variables in certain porting situations.) | |
222 | For POSIX threads, perl mutexes and condition variables correspond to | |
223 | POSIX ones. For FAKE_THREADS, mutexes are stubs and condition variables | |
224 | are implmented as lists of waiting threads. For FAKE_THREADS, a thread | |
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225 | waits on a condition variable by removing itself from the runnable |
226 | list, calling SCHEDULE to change thr to the next appropriate | |
227 | runnable thread and returning op (i.e. the new threads next op). | |
228 | This means that fake threads can only block while in PP code. | |
229 | A PP function which contains a COND_WAIT must be prepared to | |
230 | handle such restarts and can use the field "private" of struct | |
231 | thread to record its state. For fake threads, COND_SIGNAL and | |
232 | COND_BROADCAST work by putting back all the threads on the | |
233 | condition variables list into the run queue. Note that a mutex | |
234 | must *not* be held while returning from a PP function. | |
235 | ||
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236 | Perl locks and condition variables are both implemented as a |
237 | condpair_t structure, containing a mutex, an "owner" condition | |
238 | variable, an owner thread field and another condition variable). | |
239 | The structure is attached by 'm' magic to any SV. pp_lock locks | |
240 | such an object by waiting on the ownercond condition variable until | |
241 | the owner field is zero and then setting the owner field to its own | |
242 | thread pointer. The lock is semantically recursive so if the owner | |
243 | field already matches the current thread then pp_lock returns | |
244 | straight away. If the owner field has to be filled in then | |
245 | unlock_condpair is queued as an end-of-block destructor and | |
246 | that function zeroes out the owner field and signals the ownercond | |
247 | condition variable, thus waking up any other thread that wants to | |
248 | lock it. When used as a condition variable, the condpair is locked | |
249 | (involving the above wait-for-ownership and setting the owner field) | |
250 | and the spare condition variable field is used for waiting on. | |
251 | ||
252 | ||
253 | Thread states | |
254 | ||
255 | ||
256 | $t->join | |
257 | R_JOINABLE ---------------------> R_JOINED >----\ | |
258 | | \ pthread_join(t) | ^ | | |
259 | | \ | | join | pthread_join | |
260 | | \ | | | | |
261 | | \ | \------/ | |
262 | | \ | | |
263 | | \ | | |
264 | | $t->detach\ pthread_detach | | |
265 | | _\| | | |
266 | ends| R_DETACHED ends | unlink | |
267 | | \ | | |
268 | | ends \ unlink | | |
269 | | \ | | |
270 | | \ | | |
271 | | \ | | |
272 | | \ | | |
273 | | \ | | |
274 | V join detach _\| V | |
275 | ZOMBIE ----------------------------> DEAD | |
276 | pthread_join pthread_detach | |
277 | and unlink and unlink | |
278 | ||
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279 | |
280 | ||
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281 | Malcolm Beattie |
282 | mbeattie@sable.ox.ac.uk | |
69ce17de | 283 | Last updated: 27 November 1997 |
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284 | |
285 | Configure-related info updated 16 July 1998 by | |
286 | Andy Dougherty <doughera@lafayette.edu> | |
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287 | |
288 | Other minor updates 10 Feb 1999 by | |
289 | Gurusamy Sarathy |