root/gc/pthread_stop_world.c
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DEFINITIONS
This source file includes following definitions.
- GC_print_sig_mask
- GC_remove_allowed_signals
- GC_suspend_handler
- GC_suspend_handler
- GC_suspend_handler_inner
- GC_restart_handler
- GC_push_all_stacks
- GC_suspend_all
- GC_stop_world
- GC_start_world
- GC_stop_init
1 #include "private/pthread_support.h"
2
3 #if defined(GC_PTHREADS) && !defined(GC_SOLARIS_THREADS) \
4 && !defined(GC_WIN32_THREADS) && !defined(GC_DARWIN_THREADS)
5
6 #include <signal.h>
7 #include <semaphore.h>
8 #include <errno.h>
9 #include <unistd.h>
10
11 #if DEBUG_THREADS
12
13 #ifndef NSIG
14 # if defined(MAXSIG)
15 # define NSIG (MAXSIG+1)
16 # elif defined(_NSIG)
17 # define NSIG _NSIG
18 # elif defined(__SIGRTMAX)
19 # define NSIG (__SIGRTMAX+1)
20 # else
21 --> please fix it
22 # endif
23 #endif
24
25 void GC_print_sig_mask()
26 {
27 sigset_t blocked;
28 int i;
29
30 if (pthread_sigmask(SIG_BLOCK, NULL, &blocked) != 0)
31 ABORT("pthread_sigmask");
32 GC_printf0("Blocked: ");
33 for (i = 1; i < NSIG; i++) {
34 if (sigismember(&blocked, i)) { GC_printf1("%ld ",(long) i); }
35 }
36 GC_printf0("\n");
37 }
38
39 #endif
40
41 /* Remove the signals that we want to allow in thread stopping */
42 /* handler from a set. */
43 void GC_remove_allowed_signals(sigset_t *set)
44 {
45 # ifdef NO_SIGNALS
46 if (sigdelset(set, SIGINT) != 0
47 || sigdelset(set, SIGQUIT) != 0
48 || sigdelset(set, SIGABRT) != 0
49 || sigdelset(set, SIGTERM) != 0) {
50 ABORT("sigdelset() failed");
51 }
52 # endif
53
54 # ifdef MPROTECT_VDB
55 /* Handlers write to the thread structure, which is in the heap, */
56 /* and hence can trigger a protection fault. */
57 if (sigdelset(set, SIGSEGV) != 0
58 # ifdef SIGBUS
59 || sigdelset(set, SIGBUS) != 0
60 # endif
61 ) {
62 ABORT("sigdelset() failed");
63 }
64 # endif
65 }
66
67 static sigset_t suspend_handler_mask;
68
69 word GC_stop_count; /* Incremented at the beginning of GC_stop_world. */
70
71 #ifdef GC_OSF1_THREADS
72 GC_bool GC_retry_signals = TRUE;
73 #else
74 GC_bool GC_retry_signals = FALSE;
75 #endif
76
77 /*
78 * We use signals to stop threads during GC.
79 *
80 * Suspended threads wait in signal handler for SIG_THR_RESTART.
81 * That's more portable than semaphores or condition variables.
82 * (We do use sem_post from a signal handler, but that should be portable.)
83 *
84 * The thread suspension signal SIG_SUSPEND is now defined in gc_priv.h.
85 * Note that we can't just stop a thread; we need it to save its stack
86 * pointer(s) and acknowledge.
87 */
88
89 #ifndef SIG_THR_RESTART
90 # if defined(GC_HPUX_THREADS) || defined(GC_OSF1_THREADS)
91 # ifdef _SIGRTMIN
92 # define SIG_THR_RESTART _SIGRTMIN + 5
93 # else
94 # define SIG_THR_RESTART SIGRTMIN + 5
95 # endif
96 # else
97 # define SIG_THR_RESTART SIGXCPU
98 # endif
99 #endif
100
101 sem_t GC_suspend_ack_sem;
102
103 void GC_suspend_handler_inner(ptr_t sig_arg);
104
105 #if defined(IA64) || defined(HP_PA)
106 extern void GC_with_callee_saves_pushed();
107
108 void GC_suspend_handler(int sig)
109 {
110 int old_errno = errno;
111 GC_with_callee_saves_pushed(GC_suspend_handler_inner, (ptr_t)(word)sig);
112 errno = old_errno;
113 }
114
115 #else
116 /* We believe that in all other cases the full context is already */
117 /* in the signal handler frame. */
118 void GC_suspend_handler(int sig)
119 {
120 int old_errno = errno;
121 GC_suspend_handler_inner((ptr_t)(word)sig);
122 errno = old_errno;
123 }
124 #endif
125
126 void GC_suspend_handler_inner(ptr_t sig_arg)
127 {
128 int sig = (int)(word)sig_arg;
129 int dummy;
130 pthread_t my_thread = pthread_self();
131 GC_thread me;
132 # ifdef PARALLEL_MARK
133 word my_mark_no = GC_mark_no;
134 /* Marker can't proceed until we acknowledge. Thus this is */
135 /* guaranteed to be the mark_no correspending to our */
136 /* suspension, i.e. the marker can't have incremented it yet. */
137 # endif
138 word my_stop_count = GC_stop_count;
139
140 if (sig != SIG_SUSPEND) ABORT("Bad signal in suspend_handler");
141
142 #if DEBUG_THREADS
143 GC_printf1("Suspending 0x%lx\n", my_thread);
144 #endif
145
146 me = GC_lookup_thread(my_thread);
147 /* The lookup here is safe, since I'm doing this on behalf */
148 /* of a thread which holds the allocation lock in order */
149 /* to stop the world. Thus concurrent modification of the */
150 /* data structure is impossible. */
151 if (me -> stop_info.last_stop_count == my_stop_count) {
152 /* Duplicate signal. OK if we are retrying. */
153 if (!GC_retry_signals) {
154 WARN("Duplicate suspend signal in thread %lx\n",
155 pthread_self());
156 }
157 return;
158 }
159 # ifdef SPARC
160 me -> stop_info.stack_ptr = (ptr_t)GC_save_regs_in_stack();
161 # else
162 me -> stop_info.stack_ptr = (ptr_t)(&dummy);
163 # endif
164 # ifdef IA64
165 me -> backing_store_ptr = (ptr_t)GC_save_regs_in_stack();
166 # endif
167
168 /* Tell the thread that wants to stop the world that this */
169 /* thread has been stopped. Note that sem_post() is */
170 /* the only async-signal-safe primitive in LinuxThreads. */
171 sem_post(&GC_suspend_ack_sem);
172 me -> stop_info.last_stop_count = my_stop_count;
173
174 /* Wait until that thread tells us to restart by sending */
175 /* this thread a SIG_THR_RESTART signal. */
176 /* SIG_THR_RESTART should be masked at this point. Thus there */
177 /* is no race. */
178 do {
179 me->stop_info.signal = 0;
180 sigsuspend(&suspend_handler_mask); /* Wait for signal */
181 } while (me->stop_info.signal != SIG_THR_RESTART);
182 /* If the RESTART signal gets lost, we can still lose. That should be */
183 /* less likely than losing the SUSPEND signal, since we don't do much */
184 /* between the sem_post and sigsuspend. */
185 /* We'd need more handshaking to work around that, since we don't want */
186 /* to accidentally leave a RESTART signal pending, thus causing us to */
187 /* continue prematurely in a future round. */
188
189 #if DEBUG_THREADS
190 GC_printf1("Continuing 0x%lx\n", my_thread);
191 #endif
192 }
193
194 void GC_restart_handler(int sig)
195 {
196 pthread_t my_thread = pthread_self();
197 GC_thread me;
198
199 if (sig != SIG_THR_RESTART) ABORT("Bad signal in suspend_handler");
200
201 /* Let the GC_suspend_handler() know that we got a SIG_THR_RESTART. */
202 /* The lookup here is safe, since I'm doing this on behalf */
203 /* of a thread which holds the allocation lock in order */
204 /* to stop the world. Thus concurrent modification of the */
205 /* data structure is impossible. */
206 me = GC_lookup_thread(my_thread);
207 me->stop_info.signal = SIG_THR_RESTART;
208
209 /*
210 ** Note: even if we didn't do anything useful here,
211 ** it would still be necessary to have a signal handler,
212 ** rather than ignoring the signals, otherwise
213 ** the signals will not be delivered at all, and
214 ** will thus not interrupt the sigsuspend() above.
215 */
216
217 #if DEBUG_THREADS
218 GC_printf1("In GC_restart_handler for 0x%lx\n", pthread_self());
219 #endif
220 }
221
222 # ifdef IA64
223 # define IF_IA64(x) x
224 # else
225 # define IF_IA64(x)
226 # endif
227 /* We hold allocation lock. Should do exactly the right thing if the */
228 /* world is stopped. Should not fail if it isn't. */
229 void GC_push_all_stacks()
230 {
231 GC_bool found_me = FALSE;
232 int i;
233 GC_thread p;
234 ptr_t lo, hi;
235 /* On IA64, we also need to scan the register backing store. */
236 IF_IA64(ptr_t bs_lo; ptr_t bs_hi;)
237 pthread_t me = pthread_self();
238
239 if (!GC_thr_initialized) GC_thr_init();
240 #if DEBUG_THREADS
241 GC_printf1("Pushing stacks from thread 0x%lx\n", (unsigned long) me);
242 #endif
243 for (i = 0; i < THREAD_TABLE_SZ; i++) {
244 for (p = GC_threads[i]; p != 0; p = p -> next) {
245 if (p -> flags & FINISHED) continue;
246 if (pthread_equal(p -> id, me)) {
247 # ifdef SPARC
248 lo = (ptr_t)GC_save_regs_in_stack();
249 # else
250 lo = GC_approx_sp();
251 # endif
252 found_me = TRUE;
253 IF_IA64(bs_hi = (ptr_t)GC_save_regs_in_stack();)
254 } else {
255 lo = p -> stop_info.stack_ptr;
256 IF_IA64(bs_hi = p -> backing_store_ptr;)
257 }
258 if ((p -> flags & MAIN_THREAD) == 0) {
259 hi = p -> stack_end;
260 IF_IA64(bs_lo = p -> backing_store_end);
261 } else {
262 /* The original stack. */
263 hi = GC_stackbottom;
264 IF_IA64(bs_lo = BACKING_STORE_BASE;)
265 }
266 #if DEBUG_THREADS
267 GC_printf3("Stack for thread 0x%lx = [%lx,%lx)\n",
268 (unsigned long) p -> id,
269 (unsigned long) lo, (unsigned long) hi);
270 #endif
271 if (0 == lo) ABORT("GC_push_all_stacks: sp not set!\n");
272 # ifdef STACK_GROWS_UP
273 /* We got them backwards! */
274 GC_push_all_stack(hi, lo);
275 # else
276 GC_push_all_stack(lo, hi);
277 # endif
278 # ifdef IA64
279 # if DEBUG_THREADS
280 GC_printf3("Reg stack for thread 0x%lx = [%lx,%lx)\n",
281 (unsigned long) p -> id,
282 (unsigned long) bs_lo, (unsigned long) bs_hi);
283 # endif
284 if (pthread_equal(p -> id, me)) {
285 GC_push_all_eager(bs_lo, bs_hi);
286 } else {
287 GC_push_all_stack(bs_lo, bs_hi);
288 }
289 # endif
290 }
291 }
292 if (!found_me && !GC_in_thread_creation)
293 ABORT("Collecting from unknown thread.");
294 }
295
296 /* There seems to be a very rare thread stopping problem. To help us */
297 /* debug that, we save the ids of the stopping thread. */
298 pthread_t GC_stopping_thread;
299 int GC_stopping_pid;
300
301 /* We hold the allocation lock. Suspend all threads that might */
302 /* still be running. Return the number of suspend signals that */
303 /* were sent. */
304 int GC_suspend_all()
305 {
306 int n_live_threads = 0;
307 int i;
308 GC_thread p;
309 int result;
310 pthread_t my_thread = pthread_self();
311
312 GC_stopping_thread = my_thread; /* debugging only. */
313 GC_stopping_pid = getpid(); /* debugging only. */
314 for (i = 0; i < THREAD_TABLE_SZ; i++) {
315 for (p = GC_threads[i]; p != 0; p = p -> next) {
316 if (p -> id != my_thread) {
317 if (p -> flags & FINISHED) continue;
318 if (p -> stop_info.last_stop_count == GC_stop_count) continue;
319 if (p -> thread_blocked) /* Will wait */ continue;
320 n_live_threads++;
321 #if DEBUG_THREADS
322 GC_printf1("Sending suspend signal to 0x%lx\n", p -> id);
323 #endif
324
325 result = pthread_kill(p -> id, SIG_SUSPEND);
326 switch(result) {
327 case ESRCH:
328 /* Not really there anymore. Possible? */
329 n_live_threads--;
330 break;
331 case 0:
332 break;
333 default:
334 ABORT("pthread_kill failed");
335 }
336 }
337 }
338 }
339 return n_live_threads;
340 }
341
342 /* Caller holds allocation lock. */
343 void GC_stop_world()
344 {
345 int i;
346 int n_live_threads;
347 int code;
348
349 #if DEBUG_THREADS
350 GC_printf1("Stopping the world from 0x%lx\n", pthread_self());
351 #endif
352
353 /* Make sure all free list construction has stopped before we start. */
354 /* No new construction can start, since free list construction is */
355 /* required to acquire and release the GC lock before it starts, */
356 /* and we have the lock. */
357 # ifdef PARALLEL_MARK
358 GC_acquire_mark_lock();
359 GC_ASSERT(GC_fl_builder_count == 0);
360 /* We should have previously waited for it to become zero. */
361 # endif /* PARALLEL_MARK */
362 ++GC_stop_count;
363 n_live_threads = GC_suspend_all();
364
365 if (GC_retry_signals) {
366 unsigned long wait_usecs = 0; /* Total wait since retry. */
367 # define WAIT_UNIT 3000
368 # define RETRY_INTERVAL 100000
369 for (;;) {
370 int ack_count;
371
372 sem_getvalue(&GC_suspend_ack_sem, &ack_count);
373 if (ack_count == n_live_threads) break;
374 if (wait_usecs > RETRY_INTERVAL) {
375 int newly_sent = GC_suspend_all();
376
377 # ifdef CONDPRINT
378 if (GC_print_stats) {
379 GC_printf1("Resent %ld signals after timeout\n",
380 newly_sent);
381 }
382 # endif
383 sem_getvalue(&GC_suspend_ack_sem, &ack_count);
384 if (newly_sent < n_live_threads - ack_count) {
385 WARN("Lost some threads during GC_stop_world?!\n",0);
386 n_live_threads = ack_count + newly_sent;
387 }
388 wait_usecs = 0;
389 }
390 usleep(WAIT_UNIT);
391 wait_usecs += WAIT_UNIT;
392 }
393 }
394 for (i = 0; i < n_live_threads; i++) {
395 while (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
396 if (errno != EINTR) {
397 GC_err_printf1("Sem_wait returned %ld\n", (unsigned long)code);
398 ABORT("sem_wait for handler failed");
399 }
400 }
401 }
402 # ifdef PARALLEL_MARK
403 GC_release_mark_lock();
404 # endif
405 #if DEBUG_THREADS
406 GC_printf1("World stopped from 0x%lx\n", pthread_self());
407 #endif
408 GC_stopping_thread = 0; /* debugging only */
409 }
410
411 /* Caller holds allocation lock, and has held it continuously since */
412 /* the world stopped. */
413 void GC_start_world()
414 {
415 pthread_t my_thread = pthread_self();
416 register int i;
417 register GC_thread p;
418 register int n_live_threads = 0;
419 register int result;
420
421 # if DEBUG_THREADS
422 GC_printf0("World starting\n");
423 # endif
424
425 for (i = 0; i < THREAD_TABLE_SZ; i++) {
426 for (p = GC_threads[i]; p != 0; p = p -> next) {
427 if (p -> id != my_thread) {
428 if (p -> flags & FINISHED) continue;
429 if (p -> thread_blocked) continue;
430 n_live_threads++;
431 #if DEBUG_THREADS
432 GC_printf1("Sending restart signal to 0x%lx\n", p -> id);
433 #endif
434
435 result = pthread_kill(p -> id, SIG_THR_RESTART);
436 switch(result) {
437 case ESRCH:
438 /* Not really there anymore. Possible? */
439 n_live_threads--;
440 break;
441 case 0:
442 break;
443 default:
444 ABORT("pthread_kill failed");
445 }
446 }
447 }
448 }
449 #if DEBUG_THREADS
450 GC_printf0("World started\n");
451 #endif
452 }
453
454 void GC_stop_init() {
455 struct sigaction act;
456
457 if (sem_init(&GC_suspend_ack_sem, 0, 0) != 0)
458 ABORT("sem_init failed");
459
460 act.sa_flags = SA_RESTART;
461 if (sigfillset(&act.sa_mask) != 0) {
462 ABORT("sigfillset() failed");
463 }
464 GC_remove_allowed_signals(&act.sa_mask);
465 /* SIG_THR_RESTART is set in the resulting mask. */
466 /* It is unmasked by the handler when necessary. */
467 act.sa_handler = GC_suspend_handler;
468 if (sigaction(SIG_SUSPEND, &act, NULL) != 0) {
469 ABORT("Cannot set SIG_SUSPEND handler");
470 }
471
472 act.sa_handler = GC_restart_handler;
473 if (sigaction(SIG_THR_RESTART, &act, NULL) != 0) {
474 ABORT("Cannot set SIG_THR_RESTART handler");
475 }
476
477 /* Inititialize suspend_handler_mask. It excludes SIG_THR_RESTART. */
478 if (sigfillset(&suspend_handler_mask) != 0) ABORT("sigfillset() failed");
479 GC_remove_allowed_signals(&suspend_handler_mask);
480 if (sigdelset(&suspend_handler_mask, SIG_THR_RESTART) != 0)
481 ABORT("sigdelset() failed");
482
483 /* Check for GC_RETRY_SIGNALS. */
484 if (0 != GETENV("GC_RETRY_SIGNALS")) {
485 GC_retry_signals = TRUE;
486 }
487 if (0 != GETENV("GC_NO_RETRY_SIGNALS")) {
488 GC_retry_signals = FALSE;
489 }
490 # ifdef CONDPRINT
491 if (GC_print_stats && GC_retry_signals) {
492 GC_printf0("Will retry suspend signal if necessary.\n");
493 }
494 # endif
495 }
496
497 #endif