src/runtime/thread.c

   1 /*
   2  * This software is part of the SBCL system. See the README file for
   3  * more information.
   4  *
   5  * This software is derived from the CMU CL system, which was
   6  * written at Carnegie Mellon University and released into the
   7  * public domain. The software is in the public domain and is
   8  * provided with absolutely no warranty. See the COPYING and CREDITS
   9  * files for more information.
  10  */
  11
  12 #include "sbcl.h"
  13
  14 #include <stdlib.h>
  15 #include <stdio.h>
  16 #include <string.h>
  17 #ifndef LISP_FEATURE_WIN32
  18 #include <sched.h>
  19 #endif
  20 #include <signal.h>
  21 #include <stddef.h>
  22 #include <errno.h>
  23 #include <sys/types.h>
  24 #ifndef LISP_FEATURE_WIN32
  25 #include <sys/wait.h>
  26 #endif
  27
  28 #include "runtime.h"
  29 #include "validate.h"           /* for CONTROL_STACK_SIZE etc */
  30 #include "alloc.h"
  31 #include "thread.h"
  32 #include "arch.h"
  33 #include "target-arch-os.h"
  34 #include "os.h"
  35 #include "globals.h"
  36 #include "dynbind.h"
  37 #include "genesis/cons.h"
  38 #include "genesis/fdefn.h"
  39 #include "interr.h"             /* for lose() */
  40 #include "gc-internal.h"
  41
  42 #ifdef LISP_FEATURE_WIN32
  43 /*
  44  * Win32 doesn't have SIGSTKSZ, and we're not switching stacks anyway,
  45  * so define it arbitrarily
  46  */
  47 #define SIGSTKSZ 1024
  48 #endif
  49
  50 #if defined(LISP_FEATURE_DARWIN) && defined(LISP_FEATURE_SB_THREAD)
  51 #define QUEUE_FREEABLE_THREAD_STACKS
  52 #endif
  53
  54 #define ALIEN_STACK_SIZE (1*1024*1024) /* 1Mb size chosen at random */
  55
  56 struct freeable_stack {
  57 #ifdef QUEUE_FREEABLE_THREAD_STACKS
  58     struct freeable_stack *next;
  59 #endif
  60     os_thread_t os_thread;
  61     os_vm_address_t stack;
  62 };
  63
  64
  65 #ifdef QUEUE_FREEABLE_THREAD_STACKS
  66 static struct freeable_stack * volatile freeable_stack_queue = 0;
  67 static int freeable_stack_count = 0;
  68 pthread_mutex_t freeable_stack_lock = PTHREAD_MUTEX_INITIALIZER;
  69 #else
  70 static struct freeable_stack * volatile freeable_stack = 0;
  71 #endif
  72
  73 int dynamic_values_bytes=4096*sizeof(lispobj);  /* same for all threads */
  74 struct thread * volatile all_threads;
  75 extern struct interrupt_data * global_interrupt_data;
  76
  77 #ifdef LISP_FEATURE_SB_THREAD
  78 pthread_mutex_t all_threads_lock = PTHREAD_MUTEX_INITIALIZER;
  79 #endif
  80
  81 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
  82 extern lispobj call_into_lisp_first_time(lispobj fun, lispobj *args, int nargs);
  83 #endif
  84
  85 static void
  86 link_thread(struct thread *th)
  87 {
  88     if (all_threads) all_threads->prev=th;
  89     th->next=all_threads;
  90     th->prev=0;
  91     all_threads=th;
  92 }
  93
  94 #ifdef LISP_FEATURE_SB_THREAD
  95 static void
  96 unlink_thread(struct thread *th)
  97 {
  98     if (th->prev)
  99         th->prev->next = th->next;
 100     else
 101         all_threads = th->next;
 102     if (th->next)
 103         th->next->prev = th->prev;
 104 }
 105 #endif
 106
 107 static int
 108 initial_thread_trampoline(struct thread *th)
 109 {
 110     lispobj function;
 111 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
 112     lispobj *args = NULL;
 113 #endif
 114     function = th->no_tls_value_marker;
 115     th->no_tls_value_marker = NO_TLS_VALUE_MARKER_WIDETAG;
 116     if(arch_os_thread_init(th)==0) return 1;
 117     link_thread(th);
 118     th->os_thread=thread_self();
 119 #ifndef LISP_FEATURE_WIN32
 120     protect_control_stack_guard_page(1);
 121 #endif
 122
 123 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
 124     return call_into_lisp_first_time(function,args,0);
 125 #else
 126     return funcall0(function);
 127 #endif
 128 }
 129
 130 #define THREAD_STRUCT_SIZE (THREAD_CONTROL_STACK_SIZE + BINDING_STACK_SIZE + \
 131                             ALIEN_STACK_SIZE + dynamic_values_bytes + \
 132                             32 * SIGSTKSZ)
 133
 134 #ifdef LISP_FEATURE_SB_THREAD
 135
 136 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 137
 138 queue_freeable_thread_stack(struct thread *thread_to_be_cleaned_up)
 139 {
 140      if (thread_to_be_cleaned_up) {
 141         pthread_mutex_lock(&freeable_stack_lock);
 142         if (freeable_stack_queue) {
 143             struct freeable_stack *new_freeable_stack = 0, *next;
 144             next = freeable_stack_queue;
 145             while (next->next) {
 146                 next = next->next;
 147             }
 148             new_freeable_stack = (struct freeable_stack *)
 149                 os_validate(0, sizeof(struct freeable_stack));
 150             new_freeable_stack->next = NULL;
 151             new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
 152             new_freeable_stack->stack = (os_vm_address_t)
 153                 thread_to_be_cleaned_up->control_stack_start;
 154             next->next = new_freeable_stack;
 155             freeable_stack_count++;
 156         } else {
 157             struct freeable_stack *new_freeable_stack = 0;
 158             new_freeable_stack = (struct freeable_stack *)
 159                 os_validate(0, sizeof(struct freeable_stack));
 160             new_freeable_stack->next = NULL;
 161             new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
 162             new_freeable_stack->stack = (os_vm_address_t)
 163                 thread_to_be_cleaned_up->control_stack_start;
 164             freeable_stack_queue = new_freeable_stack;
 165             freeable_stack_count++;
 166         }
 167         pthread_mutex_unlock(&freeable_stack_lock);
 168     }
 169 }
 170
 171 #define FREEABLE_STACK_QUEUE_SIZE 4
 172
 173 static void
 174 free_freeable_stacks() {
 175     if (freeable_stack_queue && (freeable_stack_count > FREEABLE_STACK_QUEUE_SIZE)) {
 176         struct freeable_stack* old;
 177         pthread_mutex_lock(&freeable_stack_lock);
 178         old = freeable_stack_queue;
 179         freeable_stack_queue = old->next;
 180         freeable_stack_count--;
 181         gc_assert(pthread_join(old->os_thread, NULL) == 0);
 182         FSHOW((stderr, "freeing thread %x stack\n", old->os_thread));
 183         os_invalidate(old->stack, THREAD_STRUCT_SIZE);
 184         os_invalidate((os_vm_address_t)old, sizeof(struct freeable_stack));
 185         pthread_mutex_unlock(&freeable_stack_lock);
 186     }
 187 }
 188
 189 #else
 190 static void
 191 free_thread_stack_later(struct thread *thread_to_be_cleaned_up)
 192 {
 193     struct freeable_stack *new_freeable_stack = 0;
 194     if (thread_to_be_cleaned_up) {
 195         new_freeable_stack = (struct freeable_stack *)
 196             os_validate(0, sizeof(struct freeable_stack));
 197         new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
 198         new_freeable_stack->stack = (os_vm_address_t)
 199             thread_to_be_cleaned_up->control_stack_start;
 200     }
 201     new_freeable_stack = (struct freeable_stack *)
 202         swap_lispobjs((lispobj *)(void *)&freeable_stack,
 203                       (lispobj)new_freeable_stack);
 204     if (new_freeable_stack) {
 205         FSHOW((stderr,"/reaping %p\n", (void*) new_freeable_stack->os_thread));
 206         /* Under NPTL pthread_join really waits until the thread
 207          * exists and the stack can be safely freed. This is sadly not
 208          * mandated by the pthread spec. */
 209         gc_assert(pthread_join(new_freeable_stack->os_thread, NULL) == 0);
 210         os_invalidate(new_freeable_stack->stack, THREAD_STRUCT_SIZE);
 211         os_invalidate((os_vm_address_t) new_freeable_stack,
 212                       sizeof(struct freeable_stack));
 213     }
 214 }
 215 #endif
 216
 217 /* this is the first thing that runs in the child (which is why the
 218  * silly calling convention).  Basically it calls the user's requested
 219  * lisp function after doing arch_os_thread_init and whatever other
 220  * bookkeeping needs to be done
 221  */
 222 int
 223 new_thread_trampoline(struct thread *th)
 224 {
 225     lispobj function;
 226     int result, lock_ret;
 227
 228     FSHOW((stderr,"/creating thread %lu\n", thread_self()));
 229     function = th->no_tls_value_marker;
 230     th->no_tls_value_marker = NO_TLS_VALUE_MARKER_WIDETAG;
 231     if(arch_os_thread_init(th)==0) {
 232         /* FIXME: handle error */
 233         lose("arch_os_thread_init failed\n");
 234     }
 235
 236     th->os_thread=thread_self();
 237     protect_control_stack_guard_page(1);
 238     /* Since GC can only know about this thread from the all_threads
 239      * list and we're just adding this thread to it there is no danger
 240      * of deadlocking even with SIG_STOP_FOR_GC blocked (which it is
 241      * not). */
 242     lock_ret = pthread_mutex_lock(&all_threads_lock);
 243     gc_assert(lock_ret == 0);
 244     link_thread(th);
 245     lock_ret = pthread_mutex_unlock(&all_threads_lock);
 246     gc_assert(lock_ret == 0);
 247
 248     result = funcall0(function);
 249
 250     /* Block GC */
 251     block_blockable_signals();
 252     th->state=STATE_DEAD;
 253
 254     /* SIG_STOP_FOR_GC is blocked and GC might be waiting for this
 255      * thread, but since we are already dead it won't wait long. */
 256     lock_ret = pthread_mutex_lock(&all_threads_lock);
 257     gc_assert(lock_ret == 0);
 258
 259     gc_alloc_update_page_tables(0, &th->alloc_region);
 260     unlink_thread(th);
 261     pthread_mutex_unlock(&all_threads_lock);
 262     gc_assert(lock_ret == 0);
 263
 264     if(th->tls_cookie>=0) arch_os_thread_cleanup(th);
 265     os_invalidate((os_vm_address_t)th->interrupt_data,
 266                   (sizeof (struct interrupt_data)));
 267
 268 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 269     queue_freeable_thread_stack(th);
 270 #else
 271     free_thread_stack_later(th);
 272 #endif
 273
 274     FSHOW((stderr,"/exiting thread %p\n", thread_self()));
 275     return result;
 276 }
 277
 278 #endif /* LISP_FEATURE_SB_THREAD */
 279
 280 static void
 281 free_thread_struct(struct thread *th)
 282 {
 283     if (th->interrupt_data)
 284         os_invalidate((os_vm_address_t) th->interrupt_data,
 285                       (sizeof (struct interrupt_data)));
 286     os_invalidate((os_vm_address_t) th->control_stack_start,
 287                   THREAD_STRUCT_SIZE);
 288 }
 289
 290 /* this is called from any other thread to create the new one, and
 291  * initialize all parts of it that can be initialized from another
 292  * thread
 293  */
 294
 295 static struct thread *
 296 create_thread_struct(lispobj initial_function) {
 297     union per_thread_data *per_thread;
 298     struct thread *th=0;        /*  subdue gcc */
 299     void *spaces=0;
 300 #ifdef LISP_FEATURE_SB_THREAD
 301     int i;
 302 #endif
 303
 304     /* may as well allocate all the spaces at once: it saves us from
 305      * having to decide what to do if only some of the allocations
 306      * succeed */
 307     spaces=os_validate(0, THREAD_STRUCT_SIZE);
 308     if(!spaces)
 309          return NULL;
 310     per_thread=(union per_thread_data *)
 311         (spaces+
 312          THREAD_CONTROL_STACK_SIZE+
 313          BINDING_STACK_SIZE+
 314          ALIEN_STACK_SIZE);
 315
 316 #ifdef LISP_FEATURE_SB_THREAD
 317     for(i = 0; i < (dynamic_values_bytes / sizeof(lispobj)); i++)
 318         per_thread->dynamic_values[i] = NO_TLS_VALUE_MARKER_WIDETAG;
 319     if (all_threads == 0) {
 320         if(SymbolValue(FREE_TLS_INDEX,0)==UNBOUND_MARKER_WIDETAG) {
 321             SetSymbolValue
 322                 (FREE_TLS_INDEX,
 323                  /* FIXME: should be MAX_INTERRUPTS -1 ? */
 324                  make_fixnum(MAX_INTERRUPTS+
 325                              sizeof(struct thread)/sizeof(lispobj)),
 326                  0);
 327             SetSymbolValue(TLS_INDEX_LOCK,make_fixnum(0),0);
 328         }
 329 #define STATIC_TLS_INIT(sym,field) \
 330   ((struct symbol *)(sym-OTHER_POINTER_LOWTAG))->tls_index= \
 331   make_fixnum(THREAD_SLOT_OFFSET_WORDS(field))
 332
 333         STATIC_TLS_INIT(BINDING_STACK_START,binding_stack_start);
 334         STATIC_TLS_INIT(BINDING_STACK_POINTER,binding_stack_pointer);
 335         STATIC_TLS_INIT(CONTROL_STACK_START,control_stack_start);
 336         STATIC_TLS_INIT(CONTROL_STACK_END,control_stack_end);
 337         STATIC_TLS_INIT(ALIEN_STACK,alien_stack_pointer);
 338 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 339         STATIC_TLS_INIT(PSEUDO_ATOMIC_BITS,pseudo_atomic_bits);
 340 #endif
 341 #undef STATIC_TLS_INIT
 342     }
 343 #endif
 344
 345     th=&per_thread->thread;
 346     th->control_stack_start = spaces;
 347     th->binding_stack_start=
 348         (lispobj*)((void*)th->control_stack_start+THREAD_CONTROL_STACK_SIZE);
 349     th->control_stack_end = th->binding_stack_start;
 350     th->alien_stack_start=
 351         (lispobj*)((void*)th->binding_stack_start+BINDING_STACK_SIZE);
 352     th->binding_stack_pointer=th->binding_stack_start;
 353     th->this=th;
 354     th->os_thread=0;
 355     th->state=STATE_RUNNING;
 356 #ifdef LISP_FEATURE_STACK_GROWS_DOWNWARD_NOT_UPWARD
 357     th->alien_stack_pointer=((void *)th->alien_stack_start
 358                              + ALIEN_STACK_SIZE-N_WORD_BYTES);
 359 #else
 360     th->alien_stack_pointer=((void *)th->alien_stack_start);
 361 #endif
 362 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 363     th->pseudo_atomic_bits=0;
 364 #endif
 365 #ifdef LISP_FEATURE_GENCGC
 366     gc_set_region_empty(&th->alloc_region);
 367 #endif
 368
 369 #ifndef LISP_FEATURE_SB_THREAD
 370     /* the tls-points-into-struct-thread trick is only good for threaded
 371      * sbcl, because unithread sbcl doesn't have tls.  So, we copy the
 372      * appropriate values from struct thread here, and make sure that
 373      * we use the appropriate SymbolValue macros to access any of the
 374      * variable quantities from the C runtime.  It's not quite OAOOM,
 375      * it just feels like it */
 376     SetSymbolValue(BINDING_STACK_START,(lispobj)th->binding_stack_start,th);
 377     SetSymbolValue(CONTROL_STACK_START,(lispobj)th->control_stack_start,th);
 378     SetSymbolValue(CONTROL_STACK_END,(lispobj)th->control_stack_end,th);
 379 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 380     SetSymbolValue(BINDING_STACK_POINTER,(lispobj)th->binding_stack_pointer,th);
 381     SetSymbolValue(ALIEN_STACK,(lispobj)th->alien_stack_pointer,th);
 382     SetSymbolValue(PSEUDO_ATOMIC_BITS,(lispobj)th->pseudo_atomic_bits,th);
 383 #else
 384     current_binding_stack_pointer=th->binding_stack_pointer;
 385     current_control_stack_pointer=th->control_stack_start;
 386 #endif
 387 #endif
 388     bind_variable(CURRENT_CATCH_BLOCK,make_fixnum(0),th);
 389     bind_variable(CURRENT_UNWIND_PROTECT_BLOCK,make_fixnum(0),th);
 390     bind_variable(FREE_INTERRUPT_CONTEXT_INDEX,make_fixnum(0),th);
 391     bind_variable(INTERRUPT_PENDING, NIL,th);
 392     bind_variable(INTERRUPTS_ENABLED,T,th);
 393     bind_variable(GC_PENDING,NIL,th);
 394 #ifdef LISP_FEATURE_SB_THREAD
 395     bind_variable(STOP_FOR_GC_PENDING,NIL,th);
 396 #endif
 397
 398     th->interrupt_data = (struct interrupt_data *)
 399         os_validate(0,(sizeof (struct interrupt_data)));
 400     if (!th->interrupt_data) {
 401         free_thread_struct(th);
 402         return 0;
 403     }
 404     th->interrupt_data->pending_handler = 0;
 405     th->no_tls_value_marker=initial_function;
 406
 407     th->stepping = NIL;
 408     return th;
 409 }
 410
 411 void create_initial_thread(lispobj initial_function) {
 412     struct thread *th=create_thread_struct(initial_function);
 413     if(th) {
 414         initial_thread_trampoline(th); /* no return */
 415     } else lose("can't create initial thread\n");
 416 }
 417
 418 #ifdef LISP_FEATURE_SB_THREAD
 419
 420 #ifndef __USE_XOPEN2K
 421 extern int pthread_attr_setstack (pthread_attr_t *__attr, void *__stackaddr,
 422                                   size_t __stacksize);
 423 #endif
 424
 425 boolean create_os_thread(struct thread *th,os_thread_t *kid_tid)
 426 {
 427     /* The new thread inherits the restrictive signal mask set here,
 428      * and enables signals again when it is set up properly. */
 429     pthread_attr_t attr;
 430     sigset_t newset,oldset;
 431     boolean r=1;
 432     int retcode, initcode, sizecode, addrcode;
 433
 434     FSHOW_SIGNAL((stderr,"/create_os_thread: creating new thread\n"));
 435
 436     sigemptyset(&newset);
 437     /* Blocking deferrable signals is enough, no need to block
 438      * SIG_STOP_FOR_GC because the child process is not linked onto
 439      * all_threads until it's ready. */
 440     sigaddset_deferrable(&newset);
 441     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 442
 443 #if defined(LISP_FEATURE_DARWIN)
 444 #define CONTROL_STACK_ADJUST 8192 /* darwin wants page-aligned stacks */
 445 #else
 446 #define CONTROL_STACK_ADJUST 16
 447 #endif
 448
 449     if((initcode = pthread_attr_init(&attr)) ||
 450        /* FIXME: why do we even have this in the first place? */
 451        (pthread_attr_setstack(&attr,th->control_stack_start,
 452                               THREAD_CONTROL_STACK_SIZE-CONTROL_STACK_ADJUST)) ||
 453 #undef CONTROL_STACK_ADJUST
 454        (retcode = pthread_create
 455         (kid_tid,&attr,(void *(*)(void *))new_thread_trampoline,th))) {
 456         FSHOW_SIGNAL((stderr, "init, size, addr = %d, %d, %d\n", initcode, sizecode, addrcode));
 457         FSHOW_SIGNAL((stderr, printf("pthread_create returned %d, errno %d\n", retcode, errno)));
 458         FSHOW_SIGNAL((stderr, "wanted stack size %d, min stack size %d\n",
 459                       THREAD_CONTROL_STACK_SIZE-16, PTHREAD_STACK_MIN));
 460         if(retcode < 0) {
 461             perror("create_os_thread");
 462         }
 463         r=0;
 464     }
 465 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 466     free_freeable_stacks();
 467 #endif
 468     thread_sigmask(SIG_SETMASK,&oldset,0);
 469     return r;
 470 }
 471
 472 os_thread_t create_thread(lispobj initial_function) {
 473     struct thread *th;
 474     os_thread_t kid_tid;
 475
 476     /* Assuming that a fresh thread struct has no lisp objects in it,
 477      * linking it to all_threads can be left to the thread itself
 478      * without fear of gc lossage. initial_function violates this
 479      * assumption and must stay pinned until the child starts up. */
 480     th = create_thread_struct(initial_function);
 481     if(th==0) return 0;
 482
 483     if (create_os_thread(th,&kid_tid)) {
 484         return kid_tid;
 485     } else {
 486         free_thread_struct(th);
 487         return 0;
 488     }
 489 }
 490
 491 /* Send the signo to os_thread, retry if the rt signal queue is
 492  * full. */
 493 int
 494 kill_thread_safely(os_thread_t os_thread, int signo)
 495 {
 496     int r;
 497     /* The man page does not mention EAGAIN as a valid return value
 498      * for either pthread_kill or kill. But that's theory, this is
 499      * practice. By waiting here we assume that the delivery of this
 500      * signal is not necessary for the delivery of the signals in the
 501      * queue. In other words, we _assume_ there are no deadlocks. */
 502     while ((r=pthread_kill(os_thread,signo))==EAGAIN) {
 503         /* wait a bit then try again in the hope of the rt signal
 504          * queue not being full */
 505         FSHOW_SIGNAL((stderr,"/rt signal queue full\n"));
 506         /* FIXME: some kind of backoff (random, exponential) would be
 507          * nice. */
 508         sleep(1);
 509     }
 510     return r;
 511 }
 512
 513 int signal_interrupt_thread(os_thread_t os_thread)
 514 {
 515     int status = kill_thread_safely(os_thread, SIG_INTERRUPT_THREAD);
 516     if (status == 0) {
 517         return 0;
 518     } else if (status == ESRCH) {
 519         return -1;
 520     } else {
 521         lose("cannot send SIG_INTERRUPT_THREAD to thread=%lu: %d, %s\n",
 522              os_thread, status, strerror(status));
 523     }
 524 }
 525
 526 /* stopping the world is a two-stage process.  From this thread we signal
 527  * all the others with SIG_STOP_FOR_GC.  The handler for this signal does
 528  * the usual pseudo-atomic checks (we don't want to stop a thread while
 529  * it's in the middle of allocation) then waits for another SIG_STOP_FOR_GC.
 530  */
 531
 532 /* To avoid deadlocks when gc stops the world all clients of each
 533  * mutex must enable or disable SIG_STOP_FOR_GC for the duration of
 534  * holding the lock, but they must agree on which. */
 535 void gc_stop_the_world()
 536 {
 537     struct thread *p,*th=arch_os_get_current_thread();
 538     int status, lock_ret;
 539     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock, thread=%lu\n",
 540                   th->os_thread));
 541     /* keep threads from starting while the world is stopped. */
 542     lock_ret = pthread_mutex_lock(&all_threads_lock);      \
 543     gc_assert(lock_ret == 0);
 544
 545     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock, thread=%lu\n",
 546                   th->os_thread));
 547     /* stop all other threads by sending them SIG_STOP_FOR_GC */
 548     for(p=all_threads; p; p=p->next) {
 549         gc_assert(p->os_thread != 0);
 550         FSHOW_SIGNAL((stderr,"/gc_stop_the_world: p->state: %x\n", p->state));
 551         if((p!=th) && ((p->state==STATE_RUNNING))) {
 552             FSHOW_SIGNAL((stderr,"/gc_stop_the_world: suspending %x, os_thread %x\n",
 553                           p, p->os_thread));
 554             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 555             if (status==ESRCH) {
 556                 /* This thread has exited. */
 557                 gc_assert(p->state==STATE_DEAD);
 558             } else if (status) {
 559                 lose("cannot send suspend thread=%lu: %d, %s\n",
 560                      p->os_thread,status,strerror(status));
 561             }
 562         }
 563     }
 564     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:signals sent\n"));
 565     /* wait for the running threads to stop or finish */
 566     for(p=all_threads;p;) {
 567         FSHOW_SIGNAL((stderr,"/gc_stop_the_world: th: %p, p: %p\n", th, p));
 568         if((p!=th) && (p->state==STATE_RUNNING)) {
 569             sched_yield();
 570         } else {
 571             p=p->next;
 572         }
 573     }
 574     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:end\n"));
 575 }
 576
 577 void gc_start_the_world()
 578 {
 579     struct thread *p,*th=arch_os_get_current_thread();
 580     int status, lock_ret;
 581     /* if a resumed thread creates a new thread before we're done with
 582      * this loop, the new thread will get consed on the front of
 583      * all_threads, but it won't have been stopped so won't need
 584      * restarting */
 585     FSHOW_SIGNAL((stderr,"/gc_start_the_world:begin\n"));
 586     for(p=all_threads;p;p=p->next) {
 587         gc_assert(p->os_thread!=0);
 588         if((p!=th) && (p->state!=STATE_DEAD)) {
 589             if(p->state!=STATE_SUSPENDED) {
 590                 lose("gc_start_the_world: wrong thread state is %d\n",
 591                      fixnum_value(p->state));
 592             }
 593             FSHOW_SIGNAL((stderr, "/gc_start_the_world: resuming %lu\n",
 594                           p->os_thread));
 595             p->state=STATE_RUNNING;
 596
 597 #if defined(SIG_RESUME_FROM_GC)
 598             status=kill_thread_safely(p->os_thread,SIG_RESUME_FROM_GC);
 599 #else
 600             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 601 #endif
 602             if (status) {
 603                 lose("cannot resume thread=%lu: %d, %s\n",
 604                      p->os_thread,status,strerror(status));
 605             }
 606         }
 607     }
 608     /* If we waited here until all threads leave STATE_SUSPENDED, then
 609      * SIG_STOP_FOR_GC wouldn't need to be a rt signal. That has some
 610      * performance implications, but does away with the 'rt signal
 611      * queue full' problem. */
 612
 613     lock_ret = pthread_mutex_unlock(&all_threads_lock);
 614     gc_assert(lock_ret == 0);
 615
 616     FSHOW_SIGNAL((stderr,"/gc_start_the_world:end\n"));
 617 }
 618 #endif