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
   7 #include <signal.h>
   8 #include <semaphore.h>
   9 #include <errno.h>
  10 #include <unistd.h>
  11
  12 /* work around a dlopen issue (bug #75390), undefs to avoid warnings with redefinitions */
  13 #undef PACKAGE_BUGREPORT
  14 #undef PACKAGE_NAME
  15 #undef PACKAGE_STRING
  16 #undef PACKAGE_TARNAME
  17 #undef PACKAGE_VERSION
  18 #include "mono/utils/mono-compiler.h"
  19
  20 #ifdef MONO_DEBUGGER_SUPPORTED
  21 #include "include/libgc-mono-debugger.h"
  22 #endif
  23
  24 #if DEBUG_THREADS
  25
  26 #ifndef NSIG
  27 # if defined(MAXSIG)
  28 #  define NSIG (MAXSIG+1)
  29 # elif defined(_NSIG)
  30 #  define NSIG _NSIG
  31 # elif defined(__SIGRTMAX)
  32 #  define NSIG (__SIGRTMAX+1)
  33 # else
  34   --> please fix it
  35 # endif
  36 #endif
  37
  38 void GC_print_sig_mask()
  39 {
  40     sigset_t blocked;
  41     int i;
  42
  43     if (pthread_sigmask(SIG_BLOCK, NULL, &blocked) != 0)
  44         ABORT("pthread_sigmask");
  45     GC_printf0("Blocked: ");
  46     for (i = 1; i < NSIG; i++) {
  47         if (sigismember(&blocked, i)) { GC_printf1("%ld ",(long) i); }
  48     }
  49     GC_printf0("\n");
  50 }
  51
  52 #endif
  53
  54 /* Remove the signals that we want to allow in thread stopping  */
  55 /* handler from a set.                                          */
  56 void GC_remove_allowed_signals(sigset_t *set)
  57 {
  58 #   ifdef NO_SIGNALS
  59       if (sigdelset(set, SIGINT) != 0
  60           || sigdelset(set, SIGQUIT) != 0
  61           || sigdelset(set, SIGABRT) != 0
  62           || sigdelset(set, SIGTERM) != 0) {
  63         ABORT("sigdelset() failed");
  64       }
  65 #   endif
  66
  67 #   ifdef MPROTECT_VDB
  68       /* Handlers write to the thread structure, which is in the heap,  */
  69       /* and hence can trigger a protection fault.                      */
  70       if (sigdelset(set, SIGSEGV) != 0
  71 #         ifdef SIGBUS
  72             || sigdelset(set, SIGBUS) != 0
  73 #         endif
  74           ) {
  75         ABORT("sigdelset() failed");
  76       }
  77 #   endif
  78 }
  79
  80 static sigset_t suspend_handler_mask;
  81
  82 word GC_stop_count;     /* Incremented at the beginning of GC_stop_world. */
  83
  84 #ifdef GC_OSF1_THREADS
  85   GC_bool GC_retry_signals = TRUE;
  86 #else
  87   GC_bool GC_retry_signals = FALSE;
  88 #endif
  89
  90 /*
  91  * We use signals to stop threads during GC.
  92  *
  93  * Suspended threads wait in signal handler for SIG_THR_RESTART.
  94  * That's more portable than semaphores or condition variables.
  95  * (We do use sem_post from a signal handler, but that should be portable.)
  96  *
  97  * The thread suspension signal SIG_SUSPEND is now defined in gc_priv.h.
  98  * Note that we can't just stop a thread; we need it to save its stack
  99  * pointer(s) and acknowledge.
 100  */
 101
 102 #ifndef SIG_THR_RESTART
 103 #  if defined(GC_HPUX_THREADS) || defined(GC_OSF1_THREADS)
 104 #    ifdef _SIGRTMIN
 105 #      define SIG_THR_RESTART _SIGRTMIN + 5
 106 #    else
 107 #      define SIG_THR_RESTART SIGRTMIN + 5
 108 #    endif
 109 #  else
 110 #   define SIG_THR_RESTART SIGXCPU
 111 #  endif
 112 #endif
 113
 114 sem_t GC_suspend_ack_sem;
 115
 116 static void _GC_suspend_handler(int sig)
 117 {
 118     int dummy;
 119     pthread_t my_thread = pthread_self();
 120     GC_thread me;
 121 #   ifdef PARALLEL_MARK
 122         word my_mark_no = GC_mark_no;
 123         /* Marker can't proceed until we acknowledge.  Thus this is     */
 124         /* guaranteed to be the mark_no correspending to our            */
 125         /* suspension, i.e. the marker can't have incremented it yet.   */
 126 #   endif
 127     word my_stop_count = GC_stop_count;
 128
 129     if (sig != SIG_SUSPEND) ABORT("Bad signal in suspend_handler");
 130
 131 #if DEBUG_THREADS
 132     GC_printf1("Suspending 0x%lx\n", my_thread);
 133 #endif
 134
 135     me = GC_lookup_thread(my_thread);
 136     /* The lookup here is safe, since I'm doing this on behalf  */
 137     /* of a thread which holds the allocation lock in order     */
 138     /* to stop the world.  Thus concurrent modification of the  */
 139     /* data structure is impossible.                            */
 140     if (me -> stop_info.last_stop_count == my_stop_count) {
 141         /* Duplicate signal.  OK if we are retrying.    */
 142         if (!GC_retry_signals) {
 143             WARN("Duplicate suspend signal in thread %lx\n",
 144                  pthread_self());
 145         }
 146         return;
 147     }
 148 #   ifdef SPARC
 149         me -> stop_info.stack_ptr = (ptr_t)GC_save_regs_in_stack();
 150 #   else
 151         me -> stop_info.stack_ptr = (ptr_t)(&dummy);
 152 #   endif
 153 #   ifdef IA64
 154         me -> backing_store_ptr = (ptr_t)GC_save_regs_in_stack();
 155 #   endif
 156
 157     /* Tell the thread that wants to stop the world that this   */
 158     /* thread has been stopped.  Note that sem_post() is        */
 159     /* the only async-signal-safe primitive in LinuxThreads.    */
 160     sem_post(&GC_suspend_ack_sem);
 161     me -> stop_info.last_stop_count = my_stop_count;
 162
 163     /* Wait until that thread tells us to restart by sending    */
 164     /* this thread a SIG_THR_RESTART signal.                    */
 165     /* SIG_THR_RESTART should be masked at this point.  Thus there      */
 166     /* is no race.                                              */
 167     do {
 168             me->stop_info.signal = 0;
 169             sigsuspend(&suspend_handler_mask);        /* Wait for signal */
 170     } while (me->stop_info.signal != SIG_THR_RESTART);
 171     /* If the RESTART signal gets lost, we can still lose.  That should be  */
 172     /* less likely than losing the SUSPEND signal, since we don't do much   */
 173     /* between the sem_post and sigsuspend.                                 */
 174     /* We'd need more handshaking to work around that, since we don't want  */
 175     /* to accidentally leave a RESTART signal pending, thus causing us to   */
 176     /* continue prematurely in a future round.                              */
 177
 178     /* Tell the thread that wants to start the world that this  */
 179     /* thread has been started.  Note that sem_post() is        */
 180     /* the only async-signal-safe primitive in LinuxThreads.    */
 181     sem_post(&GC_suspend_ack_sem);
 182
 183
 184 #if DEBUG_THREADS
 185     GC_printf1("Continuing 0x%lx\n", my_thread);
 186 #endif
 187 }
 188
 189 void GC_suspend_handler(int sig)
 190 {
 191         int old_errno = errno;
 192         _GC_suspend_handler(sig);
 193         errno = old_errno;
 194 }
 195
 196 static void _GC_restart_handler(int sig)
 197 {
 198     pthread_t my_thread = pthread_self();
 199     GC_thread me;
 200
 201     if (sig != SIG_THR_RESTART) ABORT("Bad signal in suspend_handler");
 202
 203     /* Let the GC_suspend_handler() know that we got a SIG_THR_RESTART. */
 204     /* The lookup here is safe, since I'm doing this on behalf  */
 205     /* of a thread which holds the allocation lock in order     */
 206     /* to stop the world.  Thus concurrent modification of the  */
 207     /* data structure is impossible.                            */
 208     me = GC_lookup_thread(my_thread);
 209     me->stop_info.signal = SIG_THR_RESTART;
 210
 211     /*
 212     ** Note: even if we didn't do anything useful here,
 213     ** it would still be necessary to have a signal handler,
 214     ** rather than ignoring the signals, otherwise
 215     ** the signals will not be delivered at all, and
 216     ** will thus not interrupt the sigsuspend() above.
 217     */
 218
 219 #if DEBUG_THREADS
 220     GC_printf1("In GC_restart_handler for 0x%lx\n", pthread_self());
 221 #endif
 222 }
 223
 224 # ifdef IA64
 225 #   define IF_IA64(x) x
 226 # else
 227 #   define IF_IA64(x)
 228 # endif
 229 /* We hold allocation lock.  Should do exactly the right thing if the   */
 230 /* world is stopped.  Should not fail if it isn't.                      */
 231 static void pthread_push_all_stacks()
 232 {
 233     GC_bool found_me = FALSE;
 234     int i;
 235     GC_thread p;
 236     ptr_t lo, hi;
 237     /* On IA64, we also need to scan the register backing store. */
 238     IF_IA64(ptr_t bs_lo; ptr_t bs_hi;)
 239     pthread_t me = pthread_self();
 240
 241     if (!GC_thr_initialized) GC_thr_init();
 242     #if DEBUG_THREADS
 243         GC_printf1("Pushing stacks from thread 0x%lx\n", (unsigned long) me);
 244     #endif
 245     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 246       for (p = GC_threads[i]; p != 0; p = p -> next) {
 247         if (p -> flags & FINISHED) continue;
 248         if (pthread_equal(p -> id, me)) {
 249 #           ifdef SPARC
 250                 lo = (ptr_t)GC_save_regs_in_stack();
 251 #           else
 252                 lo = GC_approx_sp();
 253 #           endif
 254             found_me = TRUE;
 255             IF_IA64(bs_hi = (ptr_t)GC_save_regs_in_stack();)
 256         } else {
 257             lo = p -> stop_info.stack_ptr;
 258             IF_IA64(bs_hi = p -> backing_store_ptr;)
 259         }
 260         if ((p -> flags & MAIN_THREAD) == 0) {
 261             hi = p -> stack_end;
 262             IF_IA64(bs_lo = p -> backing_store_end);
 263         } else {
 264             /* The original stack. */
 265             hi = GC_stackbottom;
 266             IF_IA64(bs_lo = BACKING_STORE_BASE;)
 267         }
 268         #if DEBUG_THREADS
 269             GC_printf3("Stack for thread 0x%lx = [%lx,%lx)\n",
 270                 (unsigned long) p -> id,
 271                 (unsigned long) lo, (unsigned long) hi);
 272         #endif
 273         if (0 == lo) ABORT("GC_push_all_stacks: sp not set!\n");
 274 #       ifdef STACK_GROWS_UP
 275           /* We got them backwards! */
 276           GC_push_all_stack(hi, lo);
 277 #       else
 278           GC_push_all_stack(lo, hi);
 279 #       endif
 280 #       ifdef IA64
 281 #         if DEBUG_THREADS
 282             GC_printf3("Reg stack for thread 0x%lx = [%lx,%lx)\n",
 283                 (unsigned long) p -> id,
 284                 (unsigned long) bs_lo, (unsigned long) bs_hi);
 285 #         endif
 286           if (pthread_equal(p -> id, me)) {
 287             GC_push_all_eager(bs_lo, bs_hi);
 288           } else {
 289             GC_push_all_stack(bs_lo, bs_hi);
 290           }
 291 #       endif
 292       }
 293     }
 294     if (!found_me && !GC_in_thread_creation)
 295       ABORT("Collecting from unknown thread.");
 296 }
 297
 298 void GC_restart_handler(int sig)
 299 {
 300         int old_errno = errno;
 301         _GC_restart_handler (sig);
 302         errno = old_errno;
 303 }
 304
 305 /* We hold allocation lock.  Should do exactly the right thing if the   */
 306 /* world is stopped.  Should not fail if it isn't.                      */
 307 void GC_push_all_stacks()
 308 {
 309     pthread_push_all_stacks();
 310 }
 311
 312 /* There seems to be a very rare thread stopping problem.  To help us  */
 313 /* debug that, we save the ids of the stopping thread. */
 314 pthread_t GC_stopping_thread;
 315 int GC_stopping_pid;
 316
 317 /* We hold the allocation lock.  Suspend all threads that might */
 318 /* still be running.  Return the number of suspend signals that */
 319 /* were sent. */
 320 int GC_suspend_all()
 321 {
 322     int n_live_threads = 0;
 323     int i;
 324     GC_thread p;
 325     int result;
 326     pthread_t my_thread = pthread_self();
 327
 328     GC_stopping_thread = my_thread;    /* debugging only.      */
 329     GC_stopping_pid = getpid();                /* debugging only.      */
 330     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 331       for (p = GC_threads[i]; p != 0; p = p -> next) {
 332         if (p -> id != my_thread) {
 333             if (p -> flags & FINISHED) continue;
 334             if (p -> stop_info.last_stop_count == GC_stop_count) continue;
 335             if (p -> thread_blocked) /* Will wait */ continue;
 336             n_live_threads++;
 337             #if DEBUG_THREADS
 338               GC_printf1("Sending suspend signal to 0x%lx\n", p -> id);
 339             #endif
 340
 341         result = pthread_kill(p -> id, SIG_SUSPEND);
 342             switch(result) {
 343                 case ESRCH:
 344                     /* Not really there anymore.  Possible? */
 345                     n_live_threads--;
 346                     break;
 347                 case 0:
 348                     break;
 349                 default:
 350                     ABORT("pthread_kill failed");
 351             }
 352         }
 353       }
 354     }
 355     return n_live_threads;
 356 }
 357
 358 /* Caller holds allocation lock.        */
 359 static void pthread_stop_world()
 360 {
 361     int i;
 362     int n_live_threads;
 363     int code;
 364
 365     #if DEBUG_THREADS
 366     GC_printf1("Stopping the world from 0x%lx\n", pthread_self());
 367     #endif
 368
 369     n_live_threads = GC_suspend_all();
 370
 371       if (GC_retry_signals) {
 372           unsigned long wait_usecs = 0;  /* Total wait since retry.     */
 373 #         define WAIT_UNIT 3000
 374 #         define RETRY_INTERVAL 100000
 375           for (;;) {
 376               int ack_count;
 377
 378               sem_getvalue(&GC_suspend_ack_sem, &ack_count);
 379               if (ack_count == n_live_threads) break;
 380               if (wait_usecs > RETRY_INTERVAL) {
 381                   int newly_sent = GC_suspend_all();
 382
 383 #                 ifdef CONDPRINT
 384                     if (GC_print_stats) {
 385                       GC_printf1("Resent %ld signals after timeout\n",
 386                                  newly_sent);
 387                     }
 388 #                 endif
 389                   sem_getvalue(&GC_suspend_ack_sem, &ack_count);
 390                   if (newly_sent < n_live_threads - ack_count) {
 391                       WARN("Lost some threads during GC_stop_world?!\n",0);
 392                       n_live_threads = ack_count + newly_sent;
 393                   }
 394                   wait_usecs = 0;
 395               }
 396               usleep(WAIT_UNIT);
 397               wait_usecs += WAIT_UNIT;
 398           }
 399       }
 400     for (i = 0; i < n_live_threads; i++) {
 401           while (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
 402               if (errno != EINTR) {
 403                  GC_err_printf1("Sem_wait returned %ld\n", (unsigned long)code);
 404                  ABORT("sem_wait for handler failed");
 405               }
 406           }
 407     }
 408     #if DEBUG_THREADS
 409       GC_printf1("World stopped from 0x%lx\n", pthread_self());
 410     #endif
 411     GC_stopping_thread = 0;  /* debugging only */
 412 }
 413
 414 /* Caller holds allocation lock.        */
 415 void GC_stop_world()
 416 {
 417     if (GC_notify_event)
 418         GC_notify_event (GC_EVENT_PRE_STOP_WORLD);
 419     /* Make sure all free list construction has stopped before we start. */
 420     /* No new construction can start, since free list construction is   */
 421     /* required to acquire and release the GC lock before it starts,    */
 422     /* and we have the lock.                                            */
 423 #   ifdef PARALLEL_MARK
 424       GC_acquire_mark_lock();
 425       GC_ASSERT(GC_fl_builder_count == 0);
 426       /* We should have previously waited for it to become zero. */
 427 #   endif /* PARALLEL_MARK */
 428     ++GC_stop_count;
 429 #ifdef MONO_DEBUGGER_SUPPORTED
 430     if (gc_thread_vtable && gc_thread_vtable->stop_world)
 431         gc_thread_vtable->stop_world ();
 432     else
 433 #endif
 434         pthread_stop_world ();
 435 #   ifdef PARALLEL_MARK
 436       GC_release_mark_lock();
 437 #   endif
 438     if (GC_notify_event)
 439         GC_notify_event (GC_EVENT_POST_STOP_WORLD);
 440 }
 441
 442 /* Caller holds allocation lock, and has held it continuously since     */
 443 /* the world stopped.                                                   */
 444 static void pthread_start_world()
 445 {
 446     pthread_t my_thread = pthread_self();
 447     register int i;
 448     register GC_thread p;
 449     register int n_live_threads = 0;
 450     register int result;
 451     int code;
 452
 453 #   if DEBUG_THREADS
 454       GC_printf0("World starting\n");
 455 #   endif
 456     if (GC_notify_event)
 457         GC_notify_event (GC_EVENT_PRE_START_WORLD);
 458
 459     for (i = 0; i < THREAD_TABLE_SZ; i++) {
 460       for (p = GC_threads[i]; p != 0; p = p -> next) {
 461         if (p -> id != my_thread) {
 462             if (p -> flags & FINISHED) continue;
 463             if (p -> thread_blocked) continue;
 464             n_live_threads++;
 465             #if DEBUG_THREADS
 466               GC_printf1("Sending restart signal to 0x%lx\n", p -> id);
 467             #endif
 468
 469         result = pthread_kill(p -> id, SIG_THR_RESTART);
 470             switch(result) {
 471                 case ESRCH:
 472                     /* Not really there anymore.  Possible? */
 473                     n_live_threads--;
 474                     break;
 475                 case 0:
 476                     break;
 477                 default:
 478                     ABORT("pthread_kill failed");
 479             }
 480         }
 481       }
 482     }
 483
 484     #if DEBUG_THREADS
 485     GC_printf0 ("All threads signaled");
 486     #endif
 487
 488     for (i = 0; i < n_live_threads; i++) {
 489         while (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
 490             if (errno != EINTR) {
 491                 GC_err_printf1("Sem_wait returned %ld\n", (unsigned long)code);
 492                 ABORT("sem_wait for handler failed");
 493             }
 494         }
 495     }
 496
 497     if (GC_notify_event)
 498         GC_notify_event (GC_EVENT_POST_START_WORLD);
 499     #if DEBUG_THREADS
 500       GC_printf0("World started\n");
 501     #endif
 502 }
 503
 504 void GC_start_world()
 505 {
 506 #ifdef MONO_DEBUGGER_SUPPORTED
 507     if (gc_thread_vtable && gc_thread_vtable->start_world)
 508         gc_thread_vtable->start_world();
 509     else
 510 #endif
 511         pthread_start_world ();
 512 }
 513
 514 static void pthread_stop_init() {
 515     struct sigaction act;
 516
 517     if (sem_init(&GC_suspend_ack_sem, 0, 0) != 0)
 518         ABORT("sem_init failed");
 519
 520     act.sa_flags = SA_RESTART;
 521     if (sigfillset(&act.sa_mask) != 0) {
 522         ABORT("sigfillset() failed");
 523     }
 524     GC_remove_allowed_signals(&act.sa_mask);
 525     /* SIG_THR_RESTART is set in the resulting mask.            */
 526     /* It is unmasked by the handler when necessary.            */
 527     act.sa_handler = GC_suspend_handler;
 528     if (sigaction(SIG_SUSPEND, &act, NULL) != 0) {
 529         ABORT("Cannot set SIG_SUSPEND handler");
 530     }
 531
 532     act.sa_handler = GC_restart_handler;
 533     if (sigaction(SIG_THR_RESTART, &act, NULL) != 0) {
 534         ABORT("Cannot set SIG_THR_RESTART handler");
 535     }
 536
 537     /* Inititialize suspend_handler_mask. It excludes SIG_THR_RESTART. */
 538       if (sigfillset(&suspend_handler_mask) != 0) ABORT("sigfillset() failed");
 539       GC_remove_allowed_signals(&suspend_handler_mask);
 540       if (sigdelset(&suspend_handler_mask, SIG_THR_RESTART) != 0)
 541           ABORT("sigdelset() failed");
 542
 543     /* Check for GC_RETRY_SIGNALS.      */
 544       if (0 != GETENV("GC_RETRY_SIGNALS")) {
 545           GC_retry_signals = TRUE;
 546       }
 547       if (0 != GETENV("GC_NO_RETRY_SIGNALS")) {
 548           GC_retry_signals = FALSE;
 549       }
 550 #     ifdef CONDPRINT
 551           if (GC_print_stats && GC_retry_signals) {
 552               GC_printf0("Will retry suspend signal if necessary.\n");
 553           }
 554 #     endif
 555 }
 556
 557 /* We hold the allocation lock. */
 558 void GC_stop_init()
 559 {
 560 #ifdef MONO_DEBUGGER_SUPPORTED
 561     if (gc_thread_vtable && gc_thread_vtable->initialize)
 562         gc_thread_vtable->initialize ();
 563     else
 564 #endif
 565         pthread_stop_init ();
 566 }
 567
 568 #ifdef MONO_DEBUGGER_SUPPORTED
 569
 570 GCThreadFunctions *gc_thread_vtable = NULL;
 571
 572 void *
 573 GC_mono_debugger_get_stack_ptr (void)
 574 {
 575         GC_thread me;
 576
 577         me = GC_lookup_thread (pthread_self ());
 578         return &me->stop_info.stack_ptr;
 579 }
 580
 581 #endif
 582
 583 #endif