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1 | Building |
2 | |
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3 | If you want to build with multi-threading support and you are |
4 | running Linux 2.x (with the LinuxThreads library installed: |
5 | that's the linuxthreads and linuxthreads-devel RPMs for RedHat) |
6 | or Digital UNIX 4.x or Solaris 2.x for recentish x (2.5 is OK) |
7 | then you should be able to use |
8 | ./Configure -Dusethreads -Doptimize=-g -ders |
9 | make |
10 | and ignore the rest of this "Building" section. If it doesn't |
11 | work or you are using another platform which you believe supports |
12 | POSIX.1c threads then read on. |
13 | |
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14 | Omit the -e from your ./Configure arguments. For example, use |
15 | ./Configure -drs |
16 | When it offers to let you change config.sh, do so. If you already |
17 | have a config.sh then you can edit it and do |
18 | ./Configure -S |
19 | to propagate the required changes. |
20 | In ccflags, insert -DUSE_THREADS (and probably -DDEBUGGING since |
21 | that's what I've been building with). Also insert any other |
22 | arguments in there that your compiler needs to use POSIX threads. |
23 | Change optimize to -g to give you better debugging information. |
24 | Include any necessary explicit libraries in libs and change |
25 | ldflags if you need any linker flags instead or as well. |
26 | |
27 | More explicitly, for Linux (when using the standard kernel-threads |
28 | based LinuxThreads library): |
29 | Add -DUSE_THREADS -D_REENTRANT -DDEBUGGING to ccflags and cppflags |
30 | Add -lpthread to libs |
31 | Change optimize to -g |
32 | For Digital Unix 4.x: |
33 | Add -pthread -DUSE_THREADS -DDEBUGGING to ccflags |
34 | Add -DUSE_THREADS -DDEBUGGING to cppflags |
35 | Add -pthread to ldflags |
36 | Change optimize to -g |
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37 | Add -lpthread -lc_r to lddlflags |
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38 | For some reason, the extra includes for pthreads make Digital UNIX |
39 | complain fatally about the sbrk() delcaration in perl's malloc.c |
40 | so use the native malloc as follows: |
41 | Change usemymalloc to n |
42 | Zap mallocobj and mallocsrc (foo='') |
43 | Change d_mymalloc to undef |
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44 | For Solaris, do the same as for Linux above. |
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45 | |
46 | Now you can do a |
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47 | make |
48 | |
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49 | |
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50 | O/S specific bugs |
51 | |
52 | Solaris qsort uses a hidden mutex for synchronisation. If you die() |
53 | while doing a sort() then the resulting longjmp() leaves the mutex |
54 | locked so you get a deadlock the next time you try to sort(). |
55 | |
56 | LinuxThreads 0.5 has a bug which can cause file descriptor 0 to be |
57 | closed after a fork() leading to many strange symptoms. The |
58 | development version of LinuxThreads has this fixed but the following |
59 | patch can be applied to 0.5 for now: |
60 | |
61 | ----------------------------- cut here ----------------------------- |
62 | --- linuxthreads-0.5/pthread.c.ORI Mon Oct 6 13:55:50 1997 |
63 | +++ linuxthreads-0.5/pthread.c Mon Oct 6 13:57:24 1997 |
64 | @@ -312,8 +312,10 @@ |
65 | free(pthread_manager_thread_bos); |
66 | pthread_manager_thread_bos = pthread_manager_thread_tos = NULL; |
67 | /* Close the two ends of the pipe */ |
68 | - close(pthread_manager_request); |
69 | - close(pthread_manager_reader); |
70 | + if (pthread_manager_request >= 0) { |
71 | + close(pthread_manager_request); |
72 | + close(pthread_manager_reader); |
73 | + } |
74 | pthread_manager_request = pthread_manager_reader = -1; |
75 | /* Update the pid of the main thread */ |
76 | self->p_pid = getpid(); |
77 | ----------------------------- cut here ----------------------------- |
78 | |
79 | |
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80 | Building the Thread extension |
81 | |
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82 | The Thread extension is now part of the main perl distribution tree. |
83 | If you did Configure -Dusethreads then it will have been added to |
84 | the list of extensions automatically. |
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85 | |
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86 | You can try some of the tests with |
87 | cd ext/Thread |
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88 | perl -Mblib create.t |
89 | perl -Mblib join.t |
90 | perl -Mblib lock.t |
91 | perl -Mblib unsync.t |
92 | perl -Mblib unsync2.t |
93 | perl -Mblib unsync3.t |
94 | perl -Mblib io.t |
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95 | perl -Mblib queue.t |
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96 | The io one leaves a thread reading from the keyboard on stdin so |
97 | as the ping messages appear you can type lines and see them echoed. |
98 | |
99 | Try running the main perl test suite too. There are known |
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100 | failures for op/misc test 45 (tries to do local(@_) but @_ is |
101 | now lexical) and for some of the DBM/DB extensions (if there |
102 | underlying libraries were not compiled to be thread-aware). |
103 | may or may not work. |
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104 | |
105 | |
106 | Bugs |
107 | |
108 | * cond.t hasn't been redone since condition variable changed. |
109 | |
110 | * FAKE_THREADS should produce a working perl but the Thread |
111 | extension won't build with it yet. |
112 | |
113 | * There's a known memory leak (curstack isn't freed at the end |
114 | of each thread because it causes refcount problems that I |
115 | haven't tracked down yet) and there are very probably others too. |
116 | |
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117 | * There may still be races where bugs show up under contention. |
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118 | |
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119 | * Need to document "lock", Thread.pm, Queue.pm, ... |
120 | |
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121 | * Plenty of others |
122 | |
123 | |
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124 | Debugging |
125 | |
126 | Use the -DL command-line option to turn on debugging of the |
127 | multi-threading code. Under Linux, that also turns on a quick |
128 | hack I did to grab a bit of extra information from segfaults. |
129 | If you have a fancier gdb/threads setup than I do then you'll |
130 | have to delete the lines in perl.c which say |
131 | #if defined(DEBUGGING) && defined(USE_THREADS) && defined(__linux__) |
132 | DEBUG_L(signal(SIGSEGV, (void(*)(int))catch_sigsegv);); |
133 | #endif |
134 | |
135 | |
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136 | Background |
137 | |
138 | Some old globals (e.g. stack_sp, op) and some old per-interpreter |
139 | variables (e.g. tmps_stack, cxstack) move into struct thread. |
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140 | All fields of struct thread which derived from original perl |
141 | variables have names of the form Tfoo. For example, stack_sp becomes |
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142 | the field Tstack_sp of struct thread. For those fields which moved |
143 | from original perl, thread.h does |
144 | #define foo (thr->Tfoo) |
145 | This means that all functions in perl which need to use one of these |
146 | fields need an (automatic) variable thr which points at the current |
147 | thread's struct thread. For pp_foo functions, it is passed around as |
148 | an argument, for other functions they do |
149 | dTHR; |
150 | which declares and initialises thr from thread-specific data |
151 | via pthread_getspecific. If a function fails to compile with an |
152 | error about "no such variable thr", it probably just needs a dTHR |
153 | at the top. |
154 | |
155 | |
156 | Fake threads |
157 | |
158 | For FAKE_THREADS, thr is a global variable and perl schedules threads |
159 | by altering thr in between appropriate ops. The next and prev fields |
160 | of struct thread keep all fake threads on a doubly linked list and |
161 | the next_run and prev_run fields keep all runnable threads on a |
162 | doubly linked list. Mutexes are stubs for FAKE_THREADS. Condition |
163 | variables are implemented as a list of waiting threads. |
164 | |
165 | |
166 | Mutexes and condition variables |
167 | |
168 | The API is via macros MUTEX_{INIT,LOCK,UNLOCK,DESTROY} and |
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169 | COND_{INIT,WAIT,SIGNAL,BROADCAST,DESTROY}. |
170 | |
171 | A mutex is only required to be a simple, fast mutex (e.g. it does not |
172 | have to be recursive). It is only ever held across very short pieces |
173 | of code. Condition variables are only ever signalled/broadcast while |
174 | their associated mutex is held. (This constraint simplifies the |
175 | implementation of condition variables in certain porting situations.) |
176 | For POSIX threads, perl mutexes and condition variables correspond to |
177 | POSIX ones. For FAKE_THREADS, mutexes are stubs and condition variables |
178 | are implmented as lists of waiting threads. For FAKE_THREADS, a thread |
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179 | waits on a condition variable by removing itself from the runnable |
180 | list, calling SCHEDULE to change thr to the next appropriate |
181 | runnable thread and returning op (i.e. the new threads next op). |
182 | This means that fake threads can only block while in PP code. |
183 | A PP function which contains a COND_WAIT must be prepared to |
184 | handle such restarts and can use the field "private" of struct |
185 | thread to record its state. For fake threads, COND_SIGNAL and |
186 | COND_BROADCAST work by putting back all the threads on the |
187 | condition variables list into the run queue. Note that a mutex |
188 | must *not* be held while returning from a PP function. |
189 | |
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190 | Perl locks and condition variables are both implemented as a |
191 | condpair_t structure, containing a mutex, an "owner" condition |
192 | variable, an owner thread field and another condition variable). |
193 | The structure is attached by 'm' magic to any SV. pp_lock locks |
194 | such an object by waiting on the ownercond condition variable until |
195 | the owner field is zero and then setting the owner field to its own |
196 | thread pointer. The lock is semantically recursive so if the owner |
197 | field already matches the current thread then pp_lock returns |
198 | straight away. If the owner field has to be filled in then |
199 | unlock_condpair is queued as an end-of-block destructor and |
200 | that function zeroes out the owner field and signals the ownercond |
201 | condition variable, thus waking up any other thread that wants to |
202 | lock it. When used as a condition variable, the condpair is locked |
203 | (involving the above wait-for-ownership and setting the owner field) |
204 | and the spare condition variable field is used for waiting on. |
205 | |
206 | |
207 | Thread states |
208 | |
209 | |
210 | $t->join |
211 | R_JOINABLE ---------------------> R_JOINED >----\ |
212 | | \ pthread_join(t) | ^ | |
213 | | \ | | join | pthread_join |
214 | | \ | | | |
215 | | \ | \------/ |
216 | | \ | |
217 | | \ | |
218 | | $t->detach\ pthread_detach | |
219 | | _\| | |
220 | ends| R_DETACHED ends | unlink |
221 | | \ | |
222 | | ends \ unlink | |
223 | | \ | |
224 | | \ | |
225 | | \ | |
226 | | \ | |
227 | | \ | |
228 | V join detach _\| V |
229 | ZOMBIE ----------------------------> DEAD |
230 | pthread_join pthread_detach |
231 | and unlink and unlink |
232 | |
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233 | |
234 | |
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235 | Malcolm Beattie |
236 | mbeattie@sable.ox.ac.uk |
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237 | 6 November 1997 |