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 NACL
  23 volatile int __nacl_thread_suspension_needed = 0;
  24 pthread_t nacl_thread_parker = -1;
  25
  26 volatile int nacl_thread_parked[MAX_NACL_GC_THREADS];
  27 volatile int nacl_thread_used[MAX_NACL_GC_THREADS];
  28 volatile int nacl_thread_parking_inited = 0;
  29 volatile int nacl_num_gc_threads = 0;
  30 pthread_mutex_t nacl_thread_alloc_lock = PTHREAD_MUTEX_INITIALIZER;
  31 __thread int nacl_thread_idx = -1;
  32 __thread GC_thread nacl_gc_thread_self = NULL;
  33 #endif
  34
  35 #if DEBUG_THREADS
  36
  37 #ifndef NSIG
  38 # if defined(MAXSIG)
  39 #  define NSIG (MAXSIG+1)
  40 # elif defined(_NSIG)
  41 #  define NSIG _NSIG
  42 # elif defined(__SIGRTMAX)
  43 #  define NSIG (__SIGRTMAX+1)
  44 # else
  45   --> please fix it
  46 # endif
  47 #endif
  48
  49 #ifndef NACL
  50 void GC_print_sig_mask()
  51 {
  52     sigset_t blocked;
  53     int i;
  54
  55     if (pthread_sigmask(SIG_BLOCK, NULL, &blocked) != 0)
  56         ABORT("pthread_sigmask");
  57     GC_printf0("Blocked: ");
  58     for (i = 1; i < NSIG; i++) {
  59         if (sigismember(&blocked, i)) { GC_printf1("%ld ",(long) i); }
  60     }
  61     GC_printf0("\n");
  62 }
  63 #endif /* NACL */
  64 #endif
  65
  66 /* Remove the signals that we want to allow in thread stopping  */
  67 /* handler from a set.                                          */
  68 void GC_remove_allowed_signals(sigset_t *set)
  69 {
  70 #   ifdef NO_SIGNALS
  71       if (sigdelset(set, SIGINT) != 0
  72           || sigdelset(set, SIGQUIT) != 0
  73           || sigdelset(set, SIGABRT) != 0
  74           || sigdelset(set, SIGTERM) != 0) {
  75         ABORT("sigdelset() failed");
  76       }
  77 #   endif
  78
  79 #   ifdef MPROTECT_VDB
  80       /* Handlers write to the thread structure, which is in the heap,  */
  81       /* and hence can trigger a protection fault.                      */
  82       if (sigdelset(set, SIGSEGV) != 0
  83 #         ifdef SIGBUS
  84             || sigdelset(set, SIGBUS) != 0
  85 #         endif
  86           ) {
  87         ABORT("sigdelset() failed");
  88       }
  89 #   endif
  90 }
  91
  92 static sigset_t suspend_handler_mask;
  93
  94 word GC_stop_count;     /* Incremented at the beginning of GC_stop_world. */
  95
  96 #ifdef GC_OSF1_THREADS
  97   GC_bool GC_retry_signals = TRUE;
  98 #else
  99   GC_bool GC_retry_signals = FALSE;
 100 #endif
 101
 102 /*
 103  * We use signals to stop threads during GC.
 104  *
 105  * Suspended threads wait in signal handler for SIG_THR_RESTART.
 106  * That's more portable than semaphores or condition variables.
 107  * (We do use sem_post from a signal handler, but that should be portable.)
 108  *
 109  * The thread suspension signal SIG_SUSPEND is now defined in gc_priv.h.
 110  * Note that we can't just stop a thread; we need it to save its stack
 111  * pointer(s) and acknowledge.
 112  */
 113
 114 #ifndef SIG_THR_RESTART
 115 #  if defined(GC_HPUX_THREADS) || defined(GC_OSF1_THREADS)
 116 #    ifdef _SIGRTMIN
 117 #      define SIG_THR_RESTART _SIGRTMIN + 5
 118 #    else
 119 #      define SIG_THR_RESTART SIGRTMIN + 5
 120 #    endif
 121 #  else
 122 #   define SIG_THR_RESTART SIGXCPU
 123 #  endif
 124 #endif
 125
 126 sem_t GC_suspend_ack_sem;
 127
 128 static void _GC_suspend_handler(int sig)
 129 {
 130 #ifndef NACL
 131     int dummy;
 132     pthread_t my_thread = pthread_self();
 133     GC_thread me;
 134 #   ifdef PARALLEL_MARK
 135         word my_mark_no = GC_mark_no;
 136         /* Marker can't proceed until we acknowledge.  Thus this is     */
 137         /* guaranteed to be the mark_no correspending to our            */
 138         /* suspension, i.e. the marker can't have incremented it yet.   */
 139 #   endif
 140     word my_stop_count = GC_stop_count;
 141
 142     if (sig != SIG_SUSPEND) ABORT("Bad signal in suspend_handler");
 143
 144 #if DEBUG_THREADS
 145     GC_printf1("Suspending 0x%lx\n", my_thread);
 146 #endif
 147
 148     me = GC_lookup_thread(my_thread);
 149     /* The lookup here is safe, since I'm doing this on behalf  */
 150     /* of a thread which holds the allocation lock in order     */
 151     /* to stop the world.  Thus concurrent modification of the  */
 152     /* data structure is impossible.                            */
 153     if (me -> stop_info.last_stop_count == my_stop_count) {
 154         /* Duplicate signal.  OK if we are retrying.    */
 155         if (!GC_retry_signals) {
 156             WARN("Duplicate suspend signal in thread %lx\n",
 157                  pthread_self());
 158         }
 159         return;
 160     }
 161 #   ifdef SPARC
 162         me -> stop_info.stack_ptr = (ptr_t)GC_save_regs_in_stack();
 163 #   else
 164         me -> stop_info.stack_ptr = (ptr_t)(&dummy);
 165 #   endif
 166 #   ifdef IA64
 167         me -> backing_store_ptr = (ptr_t)GC_save_regs_in_stack();
 168 #   endif
 169
 170     /* Tell the thread that wants to stop the world that this   */
 171     /* thread has been stopped.  Note that sem_post() is        */
 172     /* the only async-signal-safe primitive in LinuxThreads.    */
 173     sem_post(&GC_suspend_ack_sem);
 174     me -> stop_info.last_stop_count = my_stop_count;
 175
 176     /* Wait until that thread tells us to restart by sending    */
 177     /* this thread a SIG_THR_RESTART signal.                    */
 178     /* SIG_THR_RESTART should be masked at this point.  Thus there      */
 179     /* is no race.                                              */
 180     do {
 181             me->stop_info.signal = 0;
 182             sigsuspend(&suspend_handler_mask);        /* Wait for signal */
 183     } while (me->stop_info.signal != SIG_THR_RESTART);
 184     /* If the RESTART signal gets lost, we can still lose.  That should be  */
 185     /* less likely than losing the SUSPEND signal, since we don't do much   */
 186     /* between the sem_post and sigsuspend.                                 */
 187     /* We'd need more handshaking to work around that, since we don't want  */
 188     /* to accidentally leave a RESTART signal pending, thus causing us to   */
 189     /* continue prematurely in a future round.                              */
 190
 191     /* Tell the thread that wants to start the world that this  */
 192     /* thread has been started.  Note that sem_post() is        */
 193     /* the only async-signal-safe primitive in LinuxThreads.    */
 194     sem_post(&GC_suspend_ack_sem);
 195
 196
 197 #if DEBUG_THREADS
 198     GC_printf1("Continuing 0x%lx\n", my_thread);
 199 #endif
 200
 201 #endif /* NACL */
 202 }
 203
 204 void GC_suspend_handler(int sig)
 205 {
 206         int old_errno = errno;
 207         _GC_suspend_handler(sig);
 208         errno = old_errno;
 209 }
 210
 211 static 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     /* Let the GC_suspend_handler() know that we got a SIG_THR_RESTART. */
 219     /* The lookup here is safe, since I'm doing this on behalf  */
 220     /* of a thread which holds the allocation lock in order     */
 221     /* to stop the world.  Thus concurrent modification of the  */
 222     /* data structure is impossible.                            */
 223     me = GC_lookup_thread(my_thread);
 224     me->stop_info.signal = SIG_THR_RESTART;
 225
 226     /*
 227     ** Note: even if we didn't do anything useful here,
 228     ** it would still be necessary to have a signal handler,
 229     ** rather than ignoring the signals, otherwise
 230     ** the signals will not be delivered at all, and
 231     ** will thus not interrupt the sigsuspend() above.
 232     */
 233
 234 #if DEBUG_THREADS
 235     GC_printf1("In GC_restart_handler for 0x%lx\n", pthread_self());
 236 #endif
 237 }
 238
 239 # ifdef IA64
 240 #   define IF_IA64(x) x
 241 # else
 242 #   define IF_IA64(x)
 243 # endif
 244 /* We hold allocation lock.  Should do exactly the right thing if the   */
 245 /* world is stopped.  Should not fail if it isn't.                      */
 246 static void pthread_push_all_stacks()
 247 {
 248     GC_bool found_me = FALSE;
 249     int i;
 250     GC_thread p;
 251     ptr_t lo, hi;
 252     /* On IA64, we also need to scan the register backing store. */
 253     IF_IA64(ptr_t bs_lo; ptr_t bs_hi;)
 254     pthread_t me = pthread_self();
 255
 256     if (!GC_thr_initialized) GC_thr_init();
 257     #if DEBUG_THREADS
 258         GC_printf1("Pushing stacks from thread 0x%lx\n", (unsigned long) me);
 259     #endif
 260     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 261       for (p = GC_threads[i]; p != 0; p = p -> next) {
 262         if (p -> flags & FINISHED) continue;
 263         if (pthread_equal(p -> id, me)) {
 264 #           ifdef SPARC
 265                 lo = (ptr_t)GC_save_regs_in_stack();
 266 #           else
 267                 lo = GC_approx_sp();
 268 #           endif
 269             found_me = TRUE;
 270             IF_IA64(bs_hi = (ptr_t)GC_save_regs_in_stack();)
 271         } else {
 272             lo = p -> stop_info.stack_ptr;
 273             IF_IA64(bs_hi = p -> backing_store_ptr;)
 274         }
 275         if ((p -> flags & MAIN_THREAD) == 0) {
 276             hi = p -> stack_end;
 277             IF_IA64(bs_lo = p -> backing_store_end);
 278         } else {
 279             /* The original stack. */
 280             hi = GC_stackbottom;
 281             IF_IA64(bs_lo = BACKING_STORE_BASE;)
 282         }
 283         #if DEBUG_THREADS
 284             GC_printf3("Stack for thread 0x%lx = [%lx,%lx)\n",
 285                 (unsigned long) p -> id,
 286                 (unsigned long) lo, (unsigned long) hi);
 287         #endif
 288         if (0 == lo) ABORT("GC_push_all_stacks: sp not set!\n");
 289         if (p->altstack && lo >= p->altstack && lo <= p->altstack + p->altstack_size)
 290                 hi = p->altstack + p->altstack_size;
 291        /* FIXME: Need to scan the normal stack too, but how ? */
 292
 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 HOST_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 HOST_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     int num_sleeps = 0;
 465
 466     #if DEBUG_THREADS
 467     GC_printf1("pthread_stop_world: num_threads %d\n", nacl_num_gc_threads - 1);
 468     #endif
 469     nacl_thread_parker = pthread_self();
 470     __nacl_thread_suspension_needed = 1;
 471
 472     while (1) {
 473         #define NACL_PARK_WAIT_NANOSECONDS 100000
 474         #define NANOS_PER_SECOND 1000000000
 475         int num_threads_parked = 0;
 476         struct timespec ts;
 477         int num_used = 0;
 478         /* Check the 'parked' flag for each thread the GC knows about */
 479         for (i = 0; i < MAX_NACL_GC_THREADS && num_used < nacl_num_gc_threads; i++) {
 480             if (nacl_thread_used[i] == 1) {
 481                 num_used++;
 482                 if (nacl_thread_parked[i] == 1) {
 483                     num_threads_parked++;
 484                 }
 485             }
 486         }
 487         /* -1 for the current thread */
 488         if (num_threads_parked >= nacl_num_gc_threads - 1)
 489             break;
 490         ts.tv_sec = 0;
 491         ts.tv_nsec = NACL_PARK_WAIT_NANOSECONDS;
 492         #if DEBUG_THREADS
 493         GC_printf1("sleeping waiting for %d threads to park...\n", nacl_num_gc_threads - num_threads_parked - 1);
 494         #endif
 495         nanosleep(&ts, 0);
 496         if (++num_sleeps > NANOS_PER_SECOND / NACL_PARK_WAIT_NANOSECONDS) {
 497             GC_printf1("GC appears stalled waiting for %d threads to park...\n", nacl_num_gc_threads - num_threads_parked - 1);
 498             num_sleeps = 0;
 499         }
 500     }
 501
 502 #endif /* NACL */
 503 }
 504
 505
 506 #ifdef NACL
 507
 508 #if __x86_64__
 509
 510 #define NACL_STORE_REGS()  \
 511     do {                  \
 512         __asm__ __volatile__ ("push %rbx");\
 513         __asm__ __volatile__ ("push %rbp");\
 514         __asm__ __volatile__ ("push %r12");\
 515         __asm__ __volatile__ ("push %r13");\
 516         __asm__ __volatile__ ("push %r14");\
 517         __asm__ __volatile__ ("push %r15");\
 518         __asm__ __volatile__ ("mov %%esp, %0" : "=m" (nacl_gc_thread_self->stop_info.stack_ptr));\
 519         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));\
 520         __asm__ __volatile__ ("naclasp $48, %r15");\
 521     } while (0)
 522
 523 #elif __i386__
 524
 525 #define NACL_STORE_REGS()  \
 526     do {                  \
 527         __asm__ __volatile__ ("push %ebx");\
 528         __asm__ __volatile__ ("push %ebp");\
 529         __asm__ __volatile__ ("push %esi");\
 530         __asm__ __volatile__ ("push %edi");\
 531         __asm__ __volatile__ ("mov %%esp, %0" : "=m" (nacl_gc_thread_self->stop_info.stack_ptr));\
 532         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));\
 533         __asm__ __volatile__ ("add $16, %esp");\
 534     } while (0)
 535
 536 #elif __arm__
 537
 538 #define NACL_STORE_REGS()  \
 539     do {                   \
 540         __asm__ __volatile__ (                      \
 541                 ".align 4\n\t"                      \
 542                 "bic %0, %0, #0xc0000000\n\t"       \
 543                 "str sp, [%0]\n\t"                  \
 544                 "bic %1, %1, #0xc0000000\n\t"       \
 545                 "stm %1, {r4-r8,r10-r12,lr}\n\t"    \
 546                         :                                               \
 547                         : "r" (&nacl_gc_thread_self->stop_info.stack_ptr), \
 548                          "r"(nacl_gc_thread_self->stop_info.reg_storage) \
 549                         : "memory");                 \
 550     } while (0)
 551 #else
 552
 553 #error "Please port NACL_STORE_REGS"
 554
 555 #endif
 556
 557 void nacl_pre_syscall_hook()
 558 {
 559     int local_dummy = 0;
 560     if (nacl_thread_idx != -1) {
 561         NACL_STORE_REGS();
 562         nacl_gc_thread_self->stop_info.stack_ptr = (ptr_t)(&local_dummy);
 563         nacl_thread_parked[nacl_thread_idx] = 1;
 564     }
 565 }
 566
 567 void __nacl_suspend_thread_if_needed();
 568
 569 void nacl_post_syscall_hook()
 570 {
 571     /* Calling __nacl_suspend_thread_if_needed() right away should guarantee we don't mutate the GC set. */
 572     __nacl_suspend_thread_if_needed();
 573     if (nacl_thread_idx != -1) {
 574         nacl_thread_parked[nacl_thread_idx] = 0;
 575     }
 576 }
 577
 578 void __nacl_suspend_thread_if_needed() {
 579     if (__nacl_thread_suspension_needed) {
 580         pthread_t self = pthread_self();
 581         int local_dummy = 0;
 582         /* Don't try to park the thread parker. */
 583         if (nacl_thread_parker == self)
 584             return;
 585
 586         /* This can happen when a thread is created   */
 587         /* outside of the GC system (wthread mostly). */
 588         if (nacl_thread_idx < 0)
 589             return;
 590
 591         /* If it was already 'parked', we're returning from a syscall, */
 592         /* so don't bother storing registers again, the GC has a set.  */
 593         if (!nacl_thread_parked[nacl_thread_idx]) {
 594             NACL_STORE_REGS();
 595             nacl_gc_thread_self->stop_info.stack_ptr = (ptr_t)(&local_dummy);
 596         }
 597         nacl_thread_parked[nacl_thread_idx] = 1;
 598         while (__nacl_thread_suspension_needed)
 599             ; /* spin */
 600         nacl_thread_parked[nacl_thread_idx] = 0;
 601
 602         /* Clear out the reg storage for next suspend. */
 603         memset(nacl_gc_thread_self->stop_info.reg_storage, 0, NACL_GC_REG_STORAGE_SIZE * sizeof(ptr_t));
 604     }
 605 }
 606
 607 #endif /* NACL */
 608
 609 /* Caller holds allocation lock.        */
 610 void GC_stop_world()
 611 {
 612     if (GC_notify_event)
 613         GC_notify_event (GC_EVENT_PRE_STOP_WORLD);
 614         GC_process_togglerefs ();
 615     /* Make sure all free list construction has stopped before we start. */
 616     /* No new construction can start, since free list construction is   */
 617     /* required to acquire and release the GC lock before it starts,    */
 618     /* and we have the lock.                                            */
 619 #   ifdef PARALLEL_MARK
 620       GC_acquire_mark_lock();
 621       GC_ASSERT(GC_fl_builder_count == 0);
 622       /* We should have previously waited for it to become zero. */
 623 #   endif /* PARALLEL_MARK */
 624     ++GC_stop_count;
 625         pthread_stop_world ();
 626 #   ifdef PARALLEL_MARK
 627       GC_release_mark_lock();
 628 #   endif
 629     if (GC_notify_event)
 630         GC_notify_event (GC_EVENT_POST_STOP_WORLD);
 631 }
 632
 633 /* Caller holds allocation lock, and has held it continuously since     */
 634 /* the world stopped.                                                   */
 635 static void pthread_start_world()
 636 {
 637 #ifndef NACL
 638     pthread_t my_thread = pthread_self();
 639     register int i;
 640     register GC_thread p;
 641     register int n_live_threads = 0;
 642     register int result;
 643     int code;
 644
 645 #   if DEBUG_THREADS
 646       GC_printf0("World starting\n");
 647 #   endif
 648     if (GC_notify_event)
 649         GC_notify_event (GC_EVENT_PRE_START_WORLD);
 650
 651     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 652       for (p = GC_threads[i]; p != 0; p = p -> next) {
 653         if (p -> id != my_thread) {
 654             if (p -> flags & FINISHED) continue;
 655             if (p -> thread_blocked) continue;
 656             n_live_threads++;
 657             #if DEBUG_THREADS
 658               GC_printf1("Sending restart signal to 0x%lx\n", p -> id);
 659             #endif
 660
 661 #ifndef HOST_ANDROID
 662         result = pthread_kill(p -> id, SIG_THR_RESTART);
 663 #else
 664         result = android_thread_kill(p -> kernel_id, SIG_THR_RESTART);
 665 #endif
 666             switch(result) {
 667                 case ESRCH:
 668                     /* Not really there anymore.  Possible? */
 669                     n_live_threads--;
 670                     break;
 671                 case 0:
 672                     break;
 673                 default:
 674                     ABORT("pthread_kill failed");
 675             }
 676         }
 677       }
 678     }
 679
 680     #if DEBUG_THREADS
 681     GC_printf0 ("All threads signaled");
 682     #endif
 683
 684     for (i = 0; i < n_live_threads; i++) {
 685         while (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
 686             if (errno != EINTR) {
 687                 GC_err_printf1("Sem_wait returned %ld\n", (unsigned long)code);
 688                 ABORT("sem_wait for handler failed");
 689             }
 690         }
 691     }
 692
 693     if (GC_notify_event)
 694         GC_notify_event (GC_EVENT_POST_START_WORLD);
 695     #if DEBUG_THREADS
 696       GC_printf0("World started\n");
 697     #endif
 698 #else /* NACL */
 699     if (GC_notify_event)
 700         GC_notify_event (GC_EVENT_PRE_START_WORLD);
 701 #   if DEBUG_THREADS
 702     GC_printf0("World starting\n");
 703 #   endif
 704     __nacl_thread_suspension_needed = 0;
 705     if (GC_notify_event)
 706         GC_notify_event (GC_EVENT_POST_START_WORLD);
 707 #endif /* NACL */
 708 }
 709
 710 void GC_start_world()
 711 {
 712         pthread_start_world ();
 713 }
 714
 715 static void pthread_stop_init() {
 716 #ifndef NACL
 717     struct sigaction act;
 718
 719     if (sem_init(&GC_suspend_ack_sem, 0, 0) != 0)
 720         ABORT("sem_init failed");
 721
 722     act.sa_flags = SA_RESTART;
 723     if (sigfillset(&act.sa_mask) != 0) {
 724         ABORT("sigfillset() failed");
 725     }
 726     GC_remove_allowed_signals(&act.sa_mask);
 727     /* SIG_THR_RESTART is set in the resulting mask.            */
 728     /* It is unmasked by the handler when necessary.            */
 729     act.sa_handler = GC_suspend_handler;
 730     if (sigaction(SIG_SUSPEND, &act, NULL) != 0) {
 731         ABORT("Cannot set SIG_SUSPEND handler");
 732     }
 733
 734     act.sa_handler = GC_restart_handler;
 735     if (sigaction(SIG_THR_RESTART, &act, NULL) != 0) {
 736         ABORT("Cannot set SIG_THR_RESTART handler");
 737     }
 738
 739     /* Inititialize suspend_handler_mask. It excludes SIG_THR_RESTART. */
 740       if (sigfillset(&suspend_handler_mask) != 0) ABORT("sigfillset() failed");
 741       GC_remove_allowed_signals(&suspend_handler_mask);
 742       if (sigdelset(&suspend_handler_mask, SIG_THR_RESTART) != 0)
 743           ABORT("sigdelset() failed");
 744
 745     /* Check for GC_RETRY_SIGNALS.      */
 746       if (0 != GETENV("GC_RETRY_SIGNALS")) {
 747           GC_retry_signals = TRUE;
 748       }
 749       if (0 != GETENV("GC_NO_RETRY_SIGNALS")) {
 750           GC_retry_signals = FALSE;
 751       }
 752 #     ifdef CONDPRINT
 753           if (GC_print_stats && GC_retry_signals) {
 754               GC_printf0("Will retry suspend signal if necessary.\n");
 755           }
 756 #     endif
 757 #endif /* NACL */
 758 }
 759
 760 /* We hold the allocation lock. */
 761 void GC_stop_init()
 762 {
 763         pthread_stop_init ();
 764 }
 765
 766 #endif