1 #include "private/pthread_support.h"
2
3 #if defined(GC_PTHREADS) && !defined(GC_WIN32_THREADS) && \
4 !defined(GC_DARWIN_THREADS)
5
6 #include <signal.h>
7 #include <semaphore.h>
8 #include <errno.h>
9 #include <unistd.h>
10 #include "atomic_ops.h"
11
12 #if DEBUG_THREADS
13
14 #ifndef NSIG
15 # if defined(MAXSIG)
16 # define NSIG (MAXSIG+1)
17 # elif defined(_NSIG)
18 # define NSIG _NSIG
19 # elif defined(__SIGRTMAX)
20 # define NSIG (__SIGRTMAX+1)
21 # else
22 --> please fix it
23 # endif
24 #endif
25
26 void GC_print_sig_mask()
27 {
28 sigset_t blocked;
29 int i;
30
31 if (pthread_sigmask(SIG_BLOCK, NULL, &blocked) != 0)
32 ABORT("pthread_sigmask");
33 GC_printf("Blocked: ");
34 for (i = 1; i < NSIG; i++) {
35 if (sigismember(&blocked, i)) { GC_printf("%d ", i); }
36 }
37 GC_printf("\n");
38 }
39
40 #endif
41
42 /* Remove the signals that we want to allow in thread stopping */
43 /* handler from a set. */
GC_remove_allowed_signals(sigset_t * set)44 void GC_remove_allowed_signals(sigset_t *set)
45 {
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
53 # ifdef MPROTECT_VDB
54 /* Handlers write to the thread structure, which is in the heap, */
55 /* and hence can trigger a protection fault. */
56 if (sigdelset(set, SIGSEGV) != 0
57 # ifdef SIGBUS
58 || sigdelset(set, SIGBUS) != 0
59 # endif
60 ) {
61 ABORT("sigdelset() failed");
62 }
63 # endif
64 }
65
66 static sigset_t suspend_handler_mask;
67
68 volatile AO_t GC_stop_count;
69 /* Incremented at the beginning of GC_stop_world. */
70
71 volatile AO_t GC_world_is_stopped = FALSE;
72 /* FALSE ==> it is safe for threads to restart, i.e. */
73 /* they will see another suspend signal before they */
74 /* are expected to stop (unless they have voluntarily */
75 /* stopped). */
76
77 #ifdef GC_OSF1_THREADS
78 GC_bool GC_retry_signals = TRUE;
79 #else
80 GC_bool GC_retry_signals = FALSE;
81 #endif
82
83 /*
84 * We use signals to stop threads during GC.
85 *
86 * Suspended threads wait in signal handler for SIG_THR_RESTART.
87 * That's more portable than semaphores or condition variables.
88 * (We do use sem_post from a signal handler, but that should be portable.)
89 *
90 * The thread suspension signal SIG_SUSPEND is now defined in gc_priv.h.
91 * Note that we can't just stop a thread; we need it to save its stack
92 * pointer(s) and acknowledge.
93 */
94
95 #ifndef SIG_THR_RESTART
96 # if defined(GC_HPUX_THREADS) || defined(GC_OSF1_THREADS) || defined(GC_NETBSD_THREADS)
97 # ifdef _SIGRTMIN
98 # define SIG_THR_RESTART _SIGRTMIN + 5
99 # else
100 # define SIG_THR_RESTART SIGRTMIN + 5
101 # endif
102 # else
103 # define SIG_THR_RESTART SIGXCPU
104 # endif
105 #endif
106
107 sem_t GC_suspend_ack_sem;
108
109 #ifdef GC_NETBSD_THREADS
110 # define GC_NETBSD_THREADS_WORKAROUND
111 /* It seems to be necessary to wait until threads have restarted. */
112 /* But it is unclear why that is the case. */
113 sem_t GC_restart_ack_sem;
114 #endif
115
116 void GC_suspend_handler_inner(ptr_t sig_arg, void *context);
117
118 #if defined(IA64) || defined(HP_PA) || defined(M68K)
GC_suspend_handler(int sig,siginfo_t * info,void * context)119 void GC_suspend_handler(int sig, siginfo_t *info, void *context)
120 {
121 int old_errno = errno;
122 GC_with_callee_saves_pushed(GC_suspend_handler_inner, (ptr_t)(word)sig);
123 errno = old_errno;
124 }
125 #else
126 /* We believe that in all other cases the full context is already */
127 /* in the signal handler frame. */
GC_suspend_handler(int sig,siginfo_t * info,void * context)128 void GC_suspend_handler(int sig, siginfo_t *info, void *context)
129 {
130 int old_errno = errno;
131 GC_suspend_handler_inner((ptr_t)(word)sig, context);
132 errno = old_errno;
133 }
134 #endif
135
GC_suspend_handler_inner(ptr_t sig_arg,void * context)136 void GC_suspend_handler_inner(ptr_t sig_arg, void *context)
137 {
138 int sig = (int)(word)sig_arg;
139 int dummy;
140 pthread_t my_thread = pthread_self();
141 GC_thread me;
142 # ifdef PARALLEL_MARK
143 word my_mark_no = GC_mark_no;
144 /* Marker can't proceed until we acknowledge. Thus this is */
145 /* guaranteed to be the mark_no correspending to our */
146 /* suspension, i.e. the marker can't have incremented it yet. */
147 # endif
148 AO_t my_stop_count = AO_load(&GC_stop_count);
149
150 if (sig != SIG_SUSPEND) ABORT("Bad signal in suspend_handler");
151
152 # if DEBUG_THREADS
153 GC_printf("Suspending 0x%x\n", (unsigned)my_thread);
154 # endif
155
156 me = GC_lookup_thread(my_thread);
157 /* The lookup here is safe, since I'm doing this on behalf */
158 /* of a thread which holds the allocation lock in order */
159 /* to stop the world. Thus concurrent modification of the */
160 /* data structure is impossible. */
161 if (me -> stop_info.last_stop_count == my_stop_count) {
162 /* Duplicate signal. OK if we are retrying. */
163 if (!GC_retry_signals) {
164 WARN("Duplicate suspend signal in thread %lx\n",
165 pthread_self());
166 }
167 return;
168 }
169 # ifdef SPARC
170 me -> stop_info.stack_ptr = GC_save_regs_in_stack();
171 # else
172 me -> stop_info.stack_ptr = (ptr_t)(&dummy);
173 # endif
174 # ifdef IA64
175 me -> backing_store_ptr = GC_save_regs_in_stack();
176 # endif
177
178 /* Tell the thread that wants to stop the world that this */
179 /* thread has been stopped. Note that sem_post() is */
180 /* the only async-signal-safe primitive in LinuxThreads. */
181 sem_post(&GC_suspend_ack_sem);
182 me -> stop_info.last_stop_count = my_stop_count;
183
184 /* Wait until that thread tells us to restart by sending */
185 /* this thread a SIG_THR_RESTART signal. */
186 /* SIG_THR_RESTART should be masked at this point. Thus there */
187 /* is no race. */
188 /* We do not continue until we receive a SIG_THR_RESTART, */
189 /* but we do not take that as authoritative. (We may be */
190 /* accidentally restarted by one of the user signals we */
191 /* don't block.) After we receive the signal, we use a */
192 /* primitive and expensive mechanism to wait until it's */
193 /* really safe to proceed. Under normal circumstances, */
194 /* this code should not be executed. */
195 do {
196 sigsuspend (&suspend_handler_mask);
197 } while (AO_load_acquire(&GC_world_is_stopped)
198 && AO_load(&GC_stop_count) == my_stop_count);
199 /* If the RESTART signal gets lost, we can still lose. That should be */
200 /* less likely than losing the SUSPEND signal, since we don't do much */
201 /* between the sem_post and sigsuspend. */
202 /* We'd need more handshaking to work around that. */
203 /* Simply dropping the sigsuspend call should be safe, but is unlikely */
204 /* to be efficient. */
205
206 # if DEBUG_THREADS
207 GC_printf("Continuing 0x%x\n", (unsigned)my_thread);
208 # endif
209 }
210
GC_restart_handler(int sig)211 void GC_restart_handler(int sig)
212 {
213 pthread_t my_thread = pthread_self();
214 GC_thread me;
215
216 if (sig != SIG_THR_RESTART) ABORT("Bad signal in suspend_handler");
217
218 # ifdef GC_NETBSD_THREADS_WORKAROUND
219 sem_post(&GC_restart_ack_sem);
220 # endif
221
222 /*
223 ** Note: even if we don't do anything useful here,
224 ** it would still be necessary to have a signal handler,
225 ** rather than ignoring the signals, otherwise
226 ** the signals will not be delivered at all, and
227 ** will thus not interrupt the sigsuspend() above.
228 */
229
230 # if DEBUG_THREADS
231 GC_printf("In GC_restart_handler for 0x%x\n", (unsigned)pthread_self());
232 # endif
233 }
234
235 # ifdef IA64
236 # define IF_IA64(x) x
237 # else
238 # define IF_IA64(x)
239 # endif
240 /* We hold allocation lock. Should do exactly the right thing if the */
241 /* world is stopped. Should not fail if it isn't. */
GC_push_all_stacks()242 void GC_push_all_stacks()
243 {
244 GC_bool found_me = FALSE;
245 size_t nthreads = 0;
246 int i;
247 GC_thread p;
248 ptr_t lo, hi;
249 /* On IA64, we also need to scan the register backing store. */
250 IF_IA64(ptr_t bs_lo; ptr_t bs_hi;)
251 pthread_t me = pthread_self();
252
253 if (!GC_thr_initialized) GC_thr_init();
254 # if DEBUG_THREADS
255 GC_printf("Pushing stacks from thread 0x%x\n", (unsigned) me);
256 # endif
257 for (i = 0; i < THREAD_TABLE_SZ; i++) {
258 for (p = GC_threads[i]; p != 0; p = p -> next) {
259 if (p -> flags & FINISHED) continue;
260 ++nthreads;
261 if (THREAD_EQUAL(p -> id, me)) {
262 # ifdef SPARC
263 lo = (ptr_t)GC_save_regs_in_stack();
264 # else
265 lo = GC_approx_sp();
266 # endif
267 found_me = TRUE;
268 IF_IA64(bs_hi = (ptr_t)GC_save_regs_in_stack();)
269 } else {
270 lo = p -> stop_info.stack_ptr;
271 IF_IA64(bs_hi = p -> backing_store_ptr;)
272 }
273 if ((p -> flags & MAIN_THREAD) == 0) {
274 hi = p -> stack_end;
275 IF_IA64(bs_lo = p -> backing_store_end);
276 } else {
277 /* The original stack. */
278 hi = GC_stackbottom;
279 IF_IA64(bs_lo = BACKING_STORE_BASE;)
280 }
281 # if DEBUG_THREADS
282 GC_printf("Stack for thread 0x%x = [%p,%p)\n",
283 (unsigned)(p -> id), lo, hi);
284 # endif
285 if (0 == lo) ABORT("GC_push_all_stacks: sp not set!\n");
286 # ifdef STACK_GROWS_UP
287 /* We got them backwards! */
288 GC_push_all_stack(hi, lo);
289 # else
290 GC_push_all_stack(lo, hi);
291 # endif
292 # ifdef IA64
293 # if DEBUG_THREADS
294 GC_printf("Reg stack for thread 0x%x = [%lx,%lx)\n",
295 (unsigned)p -> id, bs_lo, bs_hi);
296 # endif
297 if (THREAD_EQUAL(p -> id, me)) {
298 /* FIXME: This may add an unbounded number of entries, */
299 /* and hence overflow the mark stack, which is bad. */
300 GC_push_all_eager(bs_lo, bs_hi);
301 } else {
302 GC_push_all_stack(bs_lo, bs_hi);
303 }
304 # endif
305 }
306 }
307 if (GC_print_stats == VERBOSE) {
308 GC_log_printf("Pushed %d thread stacks\n", nthreads);
309 }
310 if (!found_me && !GC_in_thread_creation)
311 ABORT("Collecting from unknown thread.");
312 }
313
314 /* There seems to be a very rare thread stopping problem. To help us */
315 /* debug that, we save the ids of the stopping thread. */
316 pthread_t GC_stopping_thread;
317 int GC_stopping_pid;
318
319 /* We hold the allocation lock. Suspend all threads that might */
320 /* still be running. Return the number of suspend signals that */
321 /* were sent. */
GC_suspend_all()322 int GC_suspend_all()
323 {
324 int n_live_threads = 0;
325 int i;
326 GC_thread p;
327 int result;
328 pthread_t my_thread = pthread_self();
329
330 GC_stopping_thread = my_thread; /* debugging only. */
331 GC_stopping_pid = getpid(); /* debugging only. */
332 for (i = 0; i < THREAD_TABLE_SZ; i++) {
333 for (p = GC_threads[i]; p != 0; p = p -> next) {
334 if (!THREAD_EQUAL(p -> id, my_thread)) {
335 if (p -> flags & FINISHED) continue;
336 if (p -> stop_info.last_stop_count == GC_stop_count) continue;
337 if (p -> thread_blocked) /* Will wait */ continue;
338 n_live_threads++;
339 # if DEBUG_THREADS
340 GC_printf("Sending suspend signal to 0x%x\n",
341 (unsigned)(p -> id));
342 # endif
343
344 result = pthread_kill(p -> id, SIG_SUSPEND);
345 switch(result) {
346 case ESRCH:
347 /* Not really there anymore. Possible? */
348 n_live_threads--;
349 break;
350 case 0:
351 break;
352 default:
353 ABORT("pthread_kill failed");
354 }
355 }
356 }
357 }
358 return n_live_threads;
359 }
360
GC_stop_world()361 void GC_stop_world()
362 {
363 int i;
364 int n_live_threads;
365 int code;
366
367 GC_ASSERT(I_HOLD_LOCK());
368 # if DEBUG_THREADS
369 GC_printf("Stopping the world from 0x%x\n", (unsigned)pthread_self());
370 # endif
371
372 /* Make sure all free list construction has stopped before we start. */
373 /* No new construction can start, since free list construction is */
374 /* required to acquire and release the GC lock before it starts, */
375 /* and we have the lock. */
376 # ifdef PARALLEL_MARK
377 GC_acquire_mark_lock();
378 GC_ASSERT(GC_fl_builder_count == 0);
379 /* We should have previously waited for it to become zero. */
380 # endif /* PARALLEL_MARK */
381 AO_store(&GC_stop_count, GC_stop_count+1);
382 /* Only concurrent reads are possible. */
383 AO_store_release(&GC_world_is_stopped, TRUE);
384 n_live_threads = GC_suspend_all();
385
386 if (GC_retry_signals) {
387 unsigned long wait_usecs = 0; /* Total wait since retry. */
388 # define WAIT_UNIT 3000
389 # define RETRY_INTERVAL 100000
390 for (;;) {
391 int ack_count;
392
393 sem_getvalue(&GC_suspend_ack_sem, &ack_count);
394 if (ack_count == n_live_threads) break;
395 if (wait_usecs > RETRY_INTERVAL) {
396 int newly_sent = GC_suspend_all();
397
398 if (GC_print_stats) {
399 GC_log_printf("Resent %d signals after timeout\n",
400 newly_sent);
401 }
402 sem_getvalue(&GC_suspend_ack_sem, &ack_count);
403 if (newly_sent < n_live_threads - ack_count) {
404 WARN("Lost some threads during GC_stop_world?!\n",0);
405 n_live_threads = ack_count + newly_sent;
406 }
407 wait_usecs = 0;
408 }
409 usleep(WAIT_UNIT);
410 wait_usecs += WAIT_UNIT;
411 }
412 }
413 for (i = 0; i < n_live_threads; i++) {
414 retry:
415 if (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
416 /* On Linux, sem_wait is documented to always return zero.*/
417 /* But the documentation appears to be incorrect. */
418 if (errno == EINTR) {
419 /* Seems to happen with some versions of gdb. */
420 goto retry;
421 }
422 ABORT("sem_wait for handler failed");
423 }
424 }
425 # ifdef PARALLEL_MARK
426 GC_release_mark_lock();
427 # endif
428 #if DEBUG_THREADS
429 GC_printf("World stopped from 0x%x\n", (unsigned)pthread_self());
430 #endif
431 GC_stopping_thread = 0; /* debugging only */
432 }
433
434 /* Caller holds allocation lock, and has held it continuously since */
435 /* the world stopped. */
GC_start_world()436 void GC_start_world()
437 {
438 pthread_t my_thread = pthread_self();
439 register int i;
440 register GC_thread p;
441 register int n_live_threads = 0;
442 register int result;
443 # ifdef GC_NETBSD_THREADS_WORKAROUND
444 int code;
445 # endif
446
447 # if DEBUG_THREADS
448 GC_printf("World starting\n");
449 # endif
450
451 AO_store(&GC_world_is_stopped, FALSE);
452 for (i = 0; i < THREAD_TABLE_SZ; i++) {
453 for (p = GC_threads[i]; p != 0; p = p -> next) {
454 if (!THREAD_EQUAL(p -> id, my_thread)) {
455 if (p -> flags & FINISHED) continue;
456 if (p -> thread_blocked) continue;
457 n_live_threads++;
458 #if DEBUG_THREADS
459 GC_printf("Sending restart signal to 0x%x\n",
460 (unsigned)(p -> id));
461 #endif
462
463 result = pthread_kill(p -> id, SIG_THR_RESTART);
464 switch(result) {
465 case ESRCH:
466 /* Not really there anymore. Possible? */
467 n_live_threads--;
468 break;
469 case 0:
470 break;
471 default:
472 ABORT("pthread_kill failed");
473 }
474 }
475 }
476 }
477 # ifdef GC_NETBSD_THREADS_WORKAROUND
478 for (i = 0; i < n_live_threads; i++)
479 while (0 != (code = sem_wait(&GC_restart_ack_sem)))
480 if (errno != EINTR) {
481 GC_err_printf1("sem_wait() returned %ld\n",
482 (unsigned long)code);
483 ABORT("sem_wait() for restart handler failed");
484 }
485 # endif
486 # if DEBUG_THREADS
487 GC_printf("World started\n");
488 # endif
489 }
490
GC_stop_init()491 void GC_stop_init() {
492 struct sigaction act;
493
494 if (sem_init(&GC_suspend_ack_sem, 0, 0) != 0)
495 ABORT("sem_init failed");
496 # ifdef GC_NETBSD_THREADS_WORKAROUND
497 if (sem_init(&GC_restart_ack_sem, 0, 0) != 0)
498 ABORT("sem_init failed");
499 # endif
500
501 act.sa_flags = SA_RESTART | SA_SIGINFO;
502 if (sigfillset(&act.sa_mask) != 0) {
503 ABORT("sigfillset() failed");
504 }
505 GC_remove_allowed_signals(&act.sa_mask);
506 /* SIG_THR_RESTART is set in the resulting mask. */
507 /* It is unmasked by the handler when necessary. */
508 act.sa_sigaction = GC_suspend_handler;
509 if (sigaction(SIG_SUSPEND, &act, NULL) != 0) {
510 ABORT("Cannot set SIG_SUSPEND handler");
511 }
512
513 act.sa_flags &= ~ SA_SIGINFO;
514 act.sa_handler = GC_restart_handler;
515 if (sigaction(SIG_THR_RESTART, &act, NULL) != 0) {
516 ABORT("Cannot set SIG_THR_RESTART handler");
517 }
518
519 /* Inititialize suspend_handler_mask. It excludes SIG_THR_RESTART. */
520 if (sigfillset(&suspend_handler_mask) != 0) ABORT("sigfillset() failed");
521 GC_remove_allowed_signals(&suspend_handler_mask);
522 if (sigdelset(&suspend_handler_mask, SIG_THR_RESTART) != 0)
523 ABORT("sigdelset() failed");
524
525 /* Check for GC_RETRY_SIGNALS. */
526 if (0 != GETENV("GC_RETRY_SIGNALS")) {
527 GC_retry_signals = TRUE;
528 }
529 if (0 != GETENV("GC_NO_RETRY_SIGNALS")) {
530 GC_retry_signals = FALSE;
531 }
532 if (GC_print_stats && GC_retry_signals) {
533 GC_log_printf("Will retry suspend signal if necessary.\n");
534 }
535 }
536
537 #endif
538