libgc/pthread_stop_world.c

   1 #include "private/pthread_support.h"
   2
   3 #if defined(GC_PTHREADS) && !defined(GC_SOLARIS_THREADS) \
   4      && !defined(GC_IRIX_THREADS) && !defined(GC_WIN32_THREADS) \
   5      && !defined(GC_DARWIN_THREADS) && !defined(GC_AIX_THREADS) \
   6      && !defined(GC_OPENBSD_THREADS)
   7
   8 #include <signal.h>
   9 #include <semaphore.h>
  10 #include <errno.h>
  11 #include <unistd.h>
  12 #include <sys/time.h>
  13
  14 /* work around a dlopen issue (bug #75390), undefs to avoid warnings with redefinitions */
  15 #undef PACKAGE_BUGREPORT
  16 #undef PACKAGE_NAME
  17 #undef PACKAGE_STRING
  18 #undef PACKAGE_TARNAME
  19 #undef PACKAGE_VERSION
  20 #include "mono/utils/mono-compiler.h"
  21
  22 #ifdef MONO_DEBUGGER_SUPPORTED
  23 #include "include/libgc-mono-debugger.h"
  24 #endif
  25
  26 #ifdef NACL
  27 int nacl_park_threads_now = 0;
  28 pthread_t nacl_thread_parker = -1;
  29
  30 int nacl_thread_parked[MAX_NACL_GC_THREADS];
  31 int nacl_thread_used[MAX_NACL_GC_THREADS];
  32 int nacl_thread_parking_inited = 0;
  33 int nacl_num_gc_threads = 0;
  34 pthread_mutex_t nacl_thread_alloc_lock = PTHREAD_MUTEX_INITIALIZER;
  35 __thread int nacl_thread_idx = -1;
  36 __thread GC_thread nacl_gc_thread_self = NULL;
  37 #endif
  38
  39 #if DEBUG_THREADS
  40
  41 #ifndef NSIG
  42 # if defined(MAXSIG)
  43 #  define NSIG (MAXSIG+1)
  44 # elif defined(_NSIG)
  45 #  define NSIG _NSIG
  46 # elif defined(__SIGRTMAX)
  47 #  define NSIG (__SIGRTMAX+1)
  48 # else
  49   --> please fix it
  50 # endif
  51 #endif
  52
  53 #ifndef NACL
  54 void GC_print_sig_mask()
  55 {
  56     sigset_t blocked;
  57     int i;
  58
  59     if (pthread_sigmask(SIG_BLOCK, NULL, &blocked) != 0)
  60         ABORT("pthread_sigmask");
  61     GC_printf0("Blocked: ");
  62     for (i = 1; i < NSIG; i++) {
  63         if (sigismember(&blocked, i)) { GC_printf1("%ld ",(long) i); }
  64     }
  65     GC_printf0("\n");
  66 }
  67 #endif /* NACL */
  68 #endif
  69
  70 /* Remove the signals that we want to allow in thread stopping  */
  71 /* handler from a set.                                          */
  72 void GC_remove_allowed_signals(sigset_t *set)
  73 {
  74 #   ifdef NO_SIGNALS
  75       if (sigdelset(set, SIGINT) != 0
  76           || sigdelset(set, SIGQUIT) != 0
  77           || sigdelset(set, SIGABRT) != 0
  78           || sigdelset(set, SIGTERM) != 0) {
  79         ABORT("sigdelset() failed");
  80       }
  81 #   endif
  82
  83 #   ifdef MPROTECT_VDB
  84       /* Handlers write to the thread structure, which is in the heap,  */
  85       /* and hence can trigger a protection fault.                      */
  86       if (sigdelset(set, SIGSEGV) != 0
  87 #         ifdef SIGBUS
  88             || sigdelset(set, SIGBUS) != 0
  89 #         endif
  90           ) {
  91         ABORT("sigdelset() failed");
  92       }
  93 #   endif
  94 }
  95
  96 static sigset_t suspend_handler_mask;
  97
  98 word GC_stop_count;     /* Incremented at the beginning of GC_stop_world. */
  99
 100 #ifdef GC_OSF1_THREADS
 101   GC_bool GC_retry_signals = TRUE;
 102 #else
 103   GC_bool GC_retry_signals = FALSE;
 104 #endif
 105
 106 /*
 107  * We use signals to stop threads during GC.
 108  *
 109  * Suspended threads wait in signal handler for SIG_THR_RESTART.
 110  * That's more portable than semaphores or condition variables.
 111  * (We do use sem_post from a signal handler, but that should be portable.)
 112  *
 113  * The thread suspension signal SIG_SUSPEND is now defined in gc_priv.h.
 114  * Note that we can't just stop a thread; we need it to save its stack
 115  * pointer(s) and acknowledge.
 116  */
 117
 118 #ifndef SIG_THR_RESTART
 119 #  if defined(GC_HPUX_THREADS) || defined(GC_OSF1_THREADS)
 120 #    ifdef _SIGRTMIN
 121 #      define SIG_THR_RESTART _SIGRTMIN + 5
 122 #    else
 123 #      define SIG_THR_RESTART SIGRTMIN + 5
 124 #    endif
 125 #  else
 126 #   define SIG_THR_RESTART SIGXCPU
 127 #  endif
 128 #endif
 129
 130 sem_t GC_suspend_ack_sem;
 131
 132 static void _GC_suspend_handler(int sig)
 133 {
 134 #ifndef NACL
 135     int dummy;
 136     pthread_t my_thread = pthread_self();
 137     GC_thread me;
 138 #   ifdef PARALLEL_MARK
 139         word my_mark_no = GC_mark_no;
 140         /* Marker can't proceed until we acknowledge.  Thus this is     */
 141         /* guaranteed to be the mark_no correspending to our            */
 142         /* suspension, i.e. the marker can't have incremented it yet.   */
 143 #   endif
 144     word my_stop_count = GC_stop_count;
 145
 146     if (sig != SIG_SUSPEND) ABORT("Bad signal in suspend_handler");
 147
 148 #if DEBUG_THREADS
 149     GC_printf1("Suspending 0x%lx\n", my_thread);
 150 #endif
 151
 152     me = GC_lookup_thread(my_thread);
 153     /* The lookup here is safe, since I'm doing this on behalf  */
 154     /* of a thread which holds the allocation lock in order     */
 155     /* to stop the world.  Thus concurrent modification of the  */
 156     /* data structure is impossible.                            */
 157     if (me -> stop_info.last_stop_count == my_stop_count) {
 158         /* Duplicate signal.  OK if we are retrying.    */
 159         if (!GC_retry_signals) {
 160             WARN("Duplicate suspend signal in thread %lx\n",
 161                  pthread_self());
 162         }
 163         return;
 164     }
 165 #   ifdef SPARC
 166         me -> stop_info.stack_ptr = (ptr_t)GC_save_regs_in_stack();
 167 #   else
 168         me -> stop_info.stack_ptr = (ptr_t)(&dummy);
 169 #   endif
 170 #   ifdef IA64
 171         me -> backing_store_ptr = (ptr_t)GC_save_regs_in_stack();
 172 #   endif
 173
 174     /* Tell the thread that wants to stop the world that this   */
 175     /* thread has been stopped.  Note that sem_post() is        */
 176     /* the only async-signal-safe primitive in LinuxThreads.    */
 177     sem_post(&GC_suspend_ack_sem);
 178     me -> stop_info.last_stop_count = my_stop_count;
 179
 180     /* Wait until that thread tells us to restart by sending    */
 181     /* this thread a SIG_THR_RESTART signal.                    */
 182     /* SIG_THR_RESTART should be masked at this point.  Thus there      */
 183     /* is no race.                                              */
 184     do {
 185             me->stop_info.signal = 0;
 186             sigsuspend(&suspend_handler_mask);        /* Wait for signal */
 187     } while (me->stop_info.signal != SIG_THR_RESTART);
 188     /* If the RESTART signal gets lost, we can still lose.  That should be  */
 189     /* less likely than losing the SUSPEND signal, since we don't do much   */
 190     /* between the sem_post and sigsuspend.                                 */
 191     /* We'd need more handshaking to work around that, since we don't want  */
 192     /* to accidentally leave a RESTART signal pending, thus causing us to   */
 193     /* continue prematurely in a future round.                              */
 194
 195     /* Tell the thread that wants to start the world that this  */
 196     /* thread has been started.  Note that sem_post() is        */
 197     /* the only async-signal-safe primitive in LinuxThreads.    */
 198     sem_post(&GC_suspend_ack_sem);
 199
 200
 201 #if DEBUG_THREADS
 202     GC_printf1("Continuing 0x%lx\n", my_thread);
 203 #endif
 204
 205 #endif /* NACL */
 206 }
 207
 208 void GC_suspend_handler(int sig)
 209 {
 210         int old_errno = errno;
 211         _GC_suspend_handler(sig);
 212         errno = old_errno;
 213 }
 214
 215 static void _GC_restart_handler(int sig)
 216 {
 217     pthread_t my_thread = pthread_self();
 218     GC_thread me;
 219
 220     if (sig != SIG_THR_RESTART) ABORT("Bad signal in suspend_handler");
 221
 222     /* Let the GC_suspend_handler() know that we got a SIG_THR_RESTART. */
 223     /* The lookup here is safe, since I'm doing this on behalf  */
 224     /* of a thread which holds the allocation lock in order     */
 225     /* to stop the world.  Thus concurrent modification of the  */
 226     /* data structure is impossible.                            */
 227     me = GC_lookup_thread(my_thread);
 228     me->stop_info.signal = SIG_THR_RESTART;
 229
 230     /*
 231     ** Note: even if we didn't do anything useful here,
 232     ** it would still be necessary to have a signal handler,
 233     ** rather than ignoring the signals, otherwise
 234     ** the signals will not be delivered at all, and
 235     ** will thus not interrupt the sigsuspend() above.
 236     */
 237
 238 #if DEBUG_THREADS
 239     GC_printf1("In GC_restart_handler for 0x%lx\n", pthread_self());
 240 #endif
 241 }
 242
 243 # ifdef IA64
 244 #   define IF_IA64(x) x
 245 # else
 246 #   define IF_IA64(x)
 247 # endif
 248 /* We hold allocation lock.  Should do exactly the right thing if the   */
 249 /* world is stopped.  Should not fail if it isn't.                      */
 250 static void pthread_push_all_stacks()
 251 {
 252     GC_bool found_me = FALSE;
 253     int i;
 254     GC_thread p;
 255     ptr_t lo, hi;
 256     /* On IA64, we also need to scan the register backing store. */
 257     IF_IA64(ptr_t bs_lo; ptr_t bs_hi;)
 258     pthread_t me = pthread_self();
 259
 260     if (!GC_thr_initialized) GC_thr_init();
 261     #if DEBUG_THREADS
 262         GC_printf1("Pushing stacks from thread 0x%lx\n", (unsigned long) me);
 263     #endif
 264     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 265       for (p = GC_threads[i]; p != 0; p = p -> next) {
 266         if (p -> flags & FINISHED) continue;
 267         if (pthread_equal(p -> id, me)) {
 268 #           ifdef SPARC
 269                 lo = (ptr_t)GC_save_regs_in_stack();
 270 #           else
 271                 lo = GC_approx_sp();
 272 #           endif
 273             found_me = TRUE;
 274             IF_IA64(bs_hi = (ptr_t)GC_save_regs_in_stack();)
 275         } else {
 276             lo = p -> stop_info.stack_ptr;
 277             IF_IA64(bs_hi = p -> backing_store_ptr;)
 278         }
 279         if ((p -> flags & MAIN_THREAD) == 0) {
 280             hi = p -> stack_end;
 281             IF_IA64(bs_lo = p -> backing_store_end);
 282         } else {
 283             /* The original stack. */
 284             hi = GC_stackbottom;
 285             IF_IA64(bs_lo = BACKING_STORE_BASE;)
 286         }
 287         #if DEBUG_THREADS
 288             GC_printf3("Stack for thread 0x%lx = [%lx,%lx)\n",
 289                 (unsigned long) p -> id,
 290                 (unsigned long) lo, (unsigned long) hi);
 291         #endif
 292         if (0 == lo) ABORT("GC_push_all_stacks: sp not set!\n");
 293 #       ifdef STACK_GROWS_UP
 294           /* We got them backwards! */
 295           GC_push_all_stack(hi, lo);
 296 #       else
 297           GC_push_all_stack(lo, hi);
 298 #       endif
 299 #       ifdef NACL
 300           /* Push reg_storage as roots, this will cover the reg context */
 301           GC_push_all_stack(p -> stop_info.reg_storage, p -> stop_info.reg_storage + NACL_GC_REG_STORAGE_SIZE);
 302 #       endif
 303 #       ifdef IA64
 304 #         if DEBUG_THREADS
 305             GC_printf3("Reg stack for thread 0x%lx = [%lx,%lx)\n",
 306                 (unsigned long) p -> id,
 307                 (unsigned long) bs_lo, (unsigned long) bs_hi);
 308 #         endif
 309           if (pthread_equal(p -> id, me)) {
 310             GC_push_all_eager(bs_lo, bs_hi);
 311           } else {
 312             GC_push_all_stack(bs_lo, bs_hi);
 313           }
 314 #       endif
 315       }
 316     }
 317     if (!found_me && !GC_in_thread_creation)
 318       ABORT("Collecting from unknown thread.");
 319 }
 320
 321 void GC_restart_handler(int sig)
 322 {
 323         int old_errno = errno;
 324         _GC_restart_handler (sig);
 325         errno = old_errno;
 326 }
 327
 328 /* We hold allocation lock.  Should do exactly the right thing if the   */
 329 /* world is stopped.  Should not fail if it isn't.                      */
 330 void GC_push_all_stacks()
 331 {
 332     pthread_push_all_stacks();
 333 }
 334
 335 /* There seems to be a very rare thread stopping problem.  To help us  */
 336 /* debug that, we save the ids of the stopping thread. */
 337 pthread_t GC_stopping_thread;
 338 int GC_stopping_pid;
 339
 340 #ifdef PLATFORM_ANDROID
 341 static
 342 int android_thread_kill(pid_t tid, int sig)
 343 {
 344     int  ret;
 345     int  old_errno = errno;
 346
 347     ret = tkill(tid, sig);
 348     if (ret < 0) {
 349         ret = errno;
 350         errno = old_errno;
 351     }
 352
 353     return ret;
 354 }
 355 #endif
 356
 357 /* We hold the allocation lock.  Suspend all threads that might */
 358 /* still be running.  Return the number of suspend signals that */
 359 /* were sent. */
 360 int GC_suspend_all()
 361 {
 362 #ifndef NACL
 363     int n_live_threads = 0;
 364     int i;
 365     GC_thread p;
 366     int result;
 367     pthread_t my_thread = pthread_self();
 368
 369     GC_stopping_thread = my_thread;    /* debugging only.      */
 370     GC_stopping_pid = getpid();                /* debugging only.      */
 371     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 372       for (p = GC_threads[i]; p != 0; p = p -> next) {
 373         if (p -> id != my_thread) {
 374             if (p -> flags & FINISHED) continue;
 375             if (p -> stop_info.last_stop_count == GC_stop_count) continue;
 376             if (p -> thread_blocked) /* Will wait */ continue;
 377             n_live_threads++;
 378             #if DEBUG_THREADS
 379               GC_printf1("Sending suspend signal to 0x%lx\n", p -> id);
 380             #endif
 381
 382 #ifndef PLATFORM_ANDROID
 383         result = pthread_kill(p -> id, SIG_SUSPEND);
 384 #else
 385         result = android_thread_kill(p -> kernel_id, SIG_SUSPEND);
 386 #endif
 387             switch(result) {
 388                 case ESRCH:
 389                     /* Not really there anymore.  Possible? */
 390                     n_live_threads--;
 391                     break;
 392                 case 0:
 393                     break;
 394                 default:
 395                     ABORT("pthread_kill failed");
 396             }
 397         }
 398       }
 399     }
 400     return n_live_threads;
 401 #else /* NACL */
 402     return 0;
 403 #endif
 404 }
 405
 406 /* Caller holds allocation lock.        */
 407 static void pthread_stop_world()
 408 {
 409 #ifndef NACL
 410     int i;
 411     int n_live_threads;
 412     int code;
 413
 414     #if DEBUG_THREADS
 415     GC_printf1("Stopping the world from 0x%lx\n", pthread_self());
 416     #endif
 417
 418     n_live_threads = GC_suspend_all();
 419
 420       if (GC_retry_signals) {
 421           unsigned long wait_usecs = 0;  /* Total wait since retry.     */
 422 #         define WAIT_UNIT 3000
 423 #         define RETRY_INTERVAL 100000
 424           for (;;) {
 425               int ack_count;
 426
 427               sem_getvalue(&GC_suspend_ack_sem, &ack_count);
 428               if (ack_count == n_live_threads) break;
 429               if (wait_usecs > RETRY_INTERVAL) {
 430                   int newly_sent = GC_suspend_all();
 431
 432 #                 ifdef CONDPRINT
 433                     if (GC_print_stats) {
 434                       GC_printf1("Resent %ld signals after timeout\n",
 435                                  newly_sent);
 436                     }
 437 #                 endif
 438                   sem_getvalue(&GC_suspend_ack_sem, &ack_count);
 439                   if (newly_sent < n_live_threads - ack_count) {
 440                       WARN("Lost some threads during GC_stop_world?!\n",0);
 441                       n_live_threads = ack_count + newly_sent;
 442                   }
 443                   wait_usecs = 0;
 444               }
 445               usleep(WAIT_UNIT);
 446               wait_usecs += WAIT_UNIT;
 447           }
 448       }
 449     for (i = 0; i < n_live_threads; i++) {
 450           while (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
 451               if (errno != EINTR) {
 452                  GC_err_printf1("Sem_wait returned %ld\n", (unsigned long)code);
 453                  ABORT("sem_wait for handler failed");
 454               }
 455           }
 456     }
 457     #if DEBUG_THREADS
 458       GC_printf1("World stopped from 0x%lx\n", pthread_self());
 459     #endif
 460     GC_stopping_thread = 0;  /* debugging only */
 461 #else /* NACL */
 462     GC_thread p;
 463     int i;
 464
 465     #if DEBUG_THREADS
 466     GC_printf1("pthread_stop_world: num_threads %d\n", nacl_num_gc_threads - 1);
 467     #endif
 468     nacl_thread_parker = pthread_self();
 469     nacl_park_threads_now = 1;
 470
 471     while (1) {
 472         #define NACL_PARK_WAIT_NANOSECONDS 100000
 473         int num_threads_parked = 0;
 474         struct timespec ts;
 475         int num_used = 0;
 476         /* Check the 'parked' flag for each thread the GC knows about */
 477         for (i = 0; i < MAX_NACL_GC_THREADS && num_used < nacl_num_gc_threads; i++) {
 478             if (nacl_thread_used[i] == 1) {
 479                 num_used++;
 480                 if (nacl_thread_parked[i] == 1) {
 481                     num_threads_parked++;
 482                 }
 483             }
 484         }
 485         /* -1 for the current thread */
 486         if (num_threads_parked >= nacl_num_gc_threads - 1)
 487             break;
 488         ts.tv_sec = 0;
 489         ts.tv_nsec = NACL_PARK_WAIT_NANOSECONDS;
 490         #if DEBUG_THREADS
 491         GC_printf1("sleeping waiting for %d threads to park...\n", nacl_num_gc_threads - num_threads_parked - 1);
 492         #endif
 493         nanosleep(&ts, 0);
 494     }
 495
 496 #endif /* NACL */
 497 }
 498
 499
 500 #ifdef NACL
 501
 502 #if __x86_64__
 503
 504 #define NACL_STORE_REGS()  \
 505     do {                  \
 506         asm("push %rbx");\
 507         asm("push %rbp");\
 508         asm("push %r12");\
 509         asm("push %r13");\
 510         asm("push %r14");\
 511         asm("push %r15");\
 512         asm("mov %%esp, %0" : "=m" (nacl_gc_thread_self->stop_info.stack_ptr));\
 513         memcpy(nacl_gc_thread_self->stop_info.reg_storage, nacl_gc_thread_self->stop_info.stack_ptr, NACL_GC_REG_STORAGE_SIZE * sizeof(ptr_t));\
 514         asm("add $48, %esp");\
 515         asm("add %r15, %rsp");\
 516     } while (0)
 517
 518 #elif __i386__
 519
 520 #define NACL_STORE_REGS()  \
 521     do {                  \
 522         asm("push %ebx");\
 523         asm("push %ebp");\
 524         asm("push %esi");\
 525         asm("push %edi");\
 526         asm("mov %%esp, %0" : "=m" (nacl_gc_thread_self->stop_info.stack_ptr));\
 527         memcpy(nacl_gc_thread_self->stop_info.reg_storage, nacl_gc_thread_self->stop_info.stack_ptr, NACL_GC_REG_STORAGE_SIZE * sizeof(ptr_t));\
 528         asm("add $16, %esp");\
 529     } while (0)
 530
 531 #endif
 532
 533 void nacl_pre_syscall_hook()
 534 {
 535     int local_dummy = 0;
 536     if (nacl_thread_idx != -1) {
 537         NACL_STORE_REGS();
 538         nacl_gc_thread_self->stop_info.stack_ptr = (ptr_t)(&local_dummy);
 539         nacl_thread_parked[nacl_thread_idx] = 1;
 540     }
 541 }
 542
 543 void nacl_post_syscall_hook()
 544 {
 545     /* Calling __nacl_suspend_thread_if_needed() right away should guarantee we don't mutate the GC set. */
 546     __nacl_suspend_thread_if_needed();
 547     if (nacl_thread_idx != -1) {
 548         nacl_thread_parked[nacl_thread_idx] = 0;
 549     }
 550 }
 551
 552 void __nacl_suspend_thread_if_needed() {
 553     if (nacl_park_threads_now) {
 554         pthread_t self = pthread_self();
 555         int local_dummy = 0;
 556         /* Don't try to park the thread parker. */
 557         if (nacl_thread_parker == self)
 558             return;
 559
 560         /* This can happen when a thread is created   */
 561         /* outside of the GC system (wthread mostly). */
 562         if (nacl_thread_idx < 0)
 563             return;
 564
 565         /* If it was already 'parked', we're returning from a syscall, */
 566         /* so don't bother storing registers again, the GC has a set.  */
 567         if (!nacl_thread_parked[nacl_thread_idx]) {
 568             NACL_STORE_REGS();
 569             nacl_gc_thread_self->stop_info.stack_ptr = (ptr_t)(&local_dummy);
 570         }
 571         nacl_thread_parked[nacl_thread_idx] = 1;
 572         while (nacl_park_threads_now)
 573             ; /* spin */
 574         nacl_thread_parked[nacl_thread_idx] = 0;
 575
 576         /* Clear out the reg storage for next suspend. */
 577         memset(nacl_gc_thread_self->stop_info.reg_storage, 0, NACL_GC_REG_STORAGE_SIZE * sizeof(ptr_t));
 578     }
 579 }
 580
 581 #endif /* NACL */
 582
 583 /* Caller holds allocation lock.        */
 584 void GC_stop_world()
 585 {
 586     if (GC_notify_event)
 587         GC_notify_event (GC_EVENT_PRE_STOP_WORLD);
 588     /* Make sure all free list construction has stopped before we start. */
 589     /* No new construction can start, since free list construction is   */
 590     /* required to acquire and release the GC lock before it starts,    */
 591     /* and we have the lock.                                            */
 592 #   ifdef PARALLEL_MARK
 593       GC_acquire_mark_lock();
 594       GC_ASSERT(GC_fl_builder_count == 0);
 595       /* We should have previously waited for it to become zero. */
 596 #   endif /* PARALLEL_MARK */
 597     ++GC_stop_count;
 598 #ifdef MONO_DEBUGGER_SUPPORTED
 599     if (gc_thread_vtable && gc_thread_vtable->stop_world)
 600         gc_thread_vtable->stop_world ();
 601     else
 602 #endif
 603         pthread_stop_world ();
 604 #   ifdef PARALLEL_MARK
 605       GC_release_mark_lock();
 606 #   endif
 607     if (GC_notify_event)
 608         GC_notify_event (GC_EVENT_POST_STOP_WORLD);
 609 }
 610
 611 /* Caller holds allocation lock, and has held it continuously since     */
 612 /* the world stopped.                                                   */
 613 static void pthread_start_world()
 614 {
 615 #ifndef NACL
 616     pthread_t my_thread = pthread_self();
 617     register int i;
 618     register GC_thread p;
 619     register int n_live_threads = 0;
 620     register int result;
 621     int code;
 622
 623 #   if DEBUG_THREADS
 624       GC_printf0("World starting\n");
 625 #   endif
 626     if (GC_notify_event)
 627         GC_notify_event (GC_EVENT_PRE_START_WORLD);
 628
 629     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 630       for (p = GC_threads[i]; p != 0; p = p -> next) {
 631         if (p -> id != my_thread) {
 632             if (p -> flags & FINISHED) continue;
 633             if (p -> thread_blocked) continue;
 634             n_live_threads++;
 635             #if DEBUG_THREADS
 636               GC_printf1("Sending restart signal to 0x%lx\n", p -> id);
 637             #endif
 638
 639 #ifndef PLATFORM_ANDROID
 640         result = pthread_kill(p -> id, SIG_THR_RESTART);
 641 #else
 642         result = android_thread_kill(p -> kernel_id, SIG_THR_RESTART);
 643 #endif
 644             switch(result) {
 645                 case ESRCH:
 646                     /* Not really there anymore.  Possible? */
 647                     n_live_threads--;
 648                     break;
 649                 case 0:
 650                     break;
 651                 default:
 652                     ABORT("pthread_kill failed");
 653             }
 654         }
 655       }
 656     }
 657
 658     #if DEBUG_THREADS
 659     GC_printf0 ("All threads signaled");
 660     #endif
 661
 662     for (i = 0; i < n_live_threads; i++) {
 663         while (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
 664             if (errno != EINTR) {
 665                 GC_err_printf1("Sem_wait returned %ld\n", (unsigned long)code);
 666                 ABORT("sem_wait for handler failed");
 667             }
 668         }
 669     }
 670
 671     if (GC_notify_event)
 672         GC_notify_event (GC_EVENT_POST_START_WORLD);
 673     #if DEBUG_THREADS
 674       GC_printf0("World started\n");
 675     #endif
 676 #else /* NACL */
 677 #   if DEBUG_THREADS
 678     GC_printf0("World starting\n");
 679 #   endif
 680     nacl_park_threads_now = 0;
 681 #endif /* NACL */
 682 }
 683
 684 void GC_start_world()
 685 {
 686 #ifdef MONO_DEBUGGER_SUPPORTED
 687     if (gc_thread_vtable && gc_thread_vtable->start_world)
 688         gc_thread_vtable->start_world();
 689     else
 690 #endif
 691         pthread_start_world ();
 692 }
 693
 694 static void pthread_stop_init() {
 695 #ifndef NACL
 696     struct sigaction act;
 697
 698     if (sem_init(&GC_suspend_ack_sem, 0, 0) != 0)
 699         ABORT("sem_init failed");
 700
 701     act.sa_flags = SA_RESTART;
 702     if (sigfillset(&act.sa_mask) != 0) {
 703         ABORT("sigfillset() failed");
 704     }
 705     GC_remove_allowed_signals(&act.sa_mask);
 706     /* SIG_THR_RESTART is set in the resulting mask.            */
 707     /* It is unmasked by the handler when necessary.            */
 708     act.sa_handler = GC_suspend_handler;
 709     if (sigaction(SIG_SUSPEND, &act, NULL) != 0) {
 710         ABORT("Cannot set SIG_SUSPEND handler");
 711     }
 712
 713     act.sa_handler = GC_restart_handler;
 714     if (sigaction(SIG_THR_RESTART, &act, NULL) != 0) {
 715         ABORT("Cannot set SIG_THR_RESTART handler");
 716     }
 717
 718     /* Inititialize suspend_handler_mask. It excludes SIG_THR_RESTART. */
 719       if (sigfillset(&suspend_handler_mask) != 0) ABORT("sigfillset() failed");
 720       GC_remove_allowed_signals(&suspend_handler_mask);
 721       if (sigdelset(&suspend_handler_mask, SIG_THR_RESTART) != 0)
 722           ABORT("sigdelset() failed");
 723
 724     /* Check for GC_RETRY_SIGNALS.      */
 725       if (0 != GETENV("GC_RETRY_SIGNALS")) {
 726           GC_retry_signals = TRUE;
 727       }
 728       if (0 != GETENV("GC_NO_RETRY_SIGNALS")) {
 729           GC_retry_signals = FALSE;
 730       }
 731 #     ifdef CONDPRINT
 732           if (GC_print_stats && GC_retry_signals) {
 733               GC_printf0("Will retry suspend signal if necessary.\n");
 734           }
 735 #     endif
 736 #endif /* NACL */
 737 }
 738
 739 /* We hold the allocation lock. */
 740 void GC_stop_init()
 741 {
 742 #ifdef MONO_DEBUGGER_SUPPORTED
 743     if (gc_thread_vtable && gc_thread_vtable->initialize)
 744         gc_thread_vtable->initialize ();
 745     else
 746 #endif
 747         pthread_stop_init ();
 748 }
 749
 750 #ifdef MONO_DEBUGGER_SUPPORTED
 751
 752 GCThreadFunctions *gc_thread_vtable = NULL;
 753
 754 void *
 755 GC_mono_debugger_get_stack_ptr (void)
 756 {
 757         GC_thread me;
 758
 759         me = GC_lookup_thread (pthread_self ());
 760         return &me->stop_info.stack_ptr;
 761 }
 762
 763 #endif
 764
 765 #endif