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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 | |
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10 | If you want to build with multi-threading support and you are |
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11 | running one of the following: |
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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 | |
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27 | then you should be able to use |
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28 | |
29 | ./Configure -Dusethreads -des |
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30 | make |
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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 | |
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59 | For Digital Unix 4.x: |
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60 | Add -pthread to ccflags |
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61 | Add -pthread to ldflags |
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62 | Add -lpthread -lc_r to lddlflags |
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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 | |
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80 | For IRIX: |
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81 | (This should all be done automatically by the hint file). |
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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. |
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96 | For AIX: |
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97 | (This should all be done automatically by the hint file). |
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98 | Change cc to xlc_r or cc_r. |
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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 |
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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 | |
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107 | Now you can do a |
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108 | make |
109 | |
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110 | |
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111 | O/S specific bugs |
112 | |
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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. |
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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 | |
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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.) |
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164 | |
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165 | * There may still be races where bugs show up under contention. |
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166 | |
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167 | * Need to document "lock", Thread.pm, Queue.pm, ... |
168 | |
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169 | |
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170 | Debugging |
171 | |
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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__) |
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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 |
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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 |