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     FSHOW((stderr,"/creating thread %lu\n", thread_self()));
 228     function = th->no_tls_value_marker;
 229     th->no_tls_value_marker = NO_TLS_VALUE_MARKER_WIDETAG;
 230     if(arch_os_thread_init(th)==0) {
 231         /* FIXME: handle error */
 232         lose("arch_os_thread_init failed\n");
 233     }
 234
 235     th->os_thread=thread_self();
 236     protect_control_stack_guard_page(1);
 237     /* Since GC can only know about this thread from the all_threads
 238      * list and we're just adding this thread to it there is no danger
 239      * of deadlocking even with SIG_STOP_FOR_GC blocked (which it is
 240      * not). */
 241     lock_ret = pthread_mutex_lock(&all_threads_lock);
 242     gc_assert(lock_ret == 0);
 243     link_thread(th);
 244     lock_ret = pthread_mutex_unlock(&all_threads_lock);
 245     gc_assert(lock_ret == 0);
 246
 247     result = funcall0(function);
 248     th->state=STATE_DEAD;
 249
 250     /* SIG_STOP_FOR_GC is blocked and GC might be waiting for this
 251      * thread, but since we are already dead it won't wait long. */
 252     lock_ret = pthread_mutex_lock(&all_threads_lock);
 253     gc_assert(lock_ret == 0);
 254
 255     gc_alloc_update_page_tables(0, &th->alloc_region);
 256     unlink_thread(th);
 257     pthread_mutex_unlock(&all_threads_lock);
 258     gc_assert(lock_ret == 0);
 259
 260     if(th->tls_cookie>=0) arch_os_thread_cleanup(th);
 261     os_invalidate((os_vm_address_t)th->interrupt_data,
 262                   (sizeof (struct interrupt_data)));
 263
 264 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 265     queue_freeable_thread_stack(th);
 266 #else
 267     free_thread_stack_later(th);
 268 #endif
 269
 270     FSHOW((stderr,"/exiting thread %p\n", thread_self()));
 271     return result;
 272 }
 273
 274 #endif /* LISP_FEATURE_SB_THREAD */
 275
 276 static void
 277 free_thread_struct(struct thread *th)
 278 {
 279     if (th->interrupt_data)
 280         os_invalidate((os_vm_address_t) th->interrupt_data,
 281                       (sizeof (struct interrupt_data)));
 282     os_invalidate((os_vm_address_t) th->control_stack_start,
 283                   THREAD_STRUCT_SIZE);
 284 }
 285
 286 /* this is called from any other thread to create the new one, and
 287  * initialize all parts of it that can be initialized from another
 288  * thread
 289  */
 290
 291 static struct thread *
 292 create_thread_struct(lispobj initial_function) {
 293     union per_thread_data *per_thread;
 294     struct thread *th=0;        /*  subdue gcc */
 295     void *spaces=0;
 296 #ifdef LISP_FEATURE_SB_THREAD
 297     int i;
 298 #endif
 299
 300     /* may as well allocate all the spaces at once: it saves us from
 301      * having to decide what to do if only some of the allocations
 302      * succeed */
 303     spaces=os_validate(0, THREAD_STRUCT_SIZE);
 304     if(!spaces)
 305          return NULL;
 306     per_thread=(union per_thread_data *)
 307         (spaces+
 308          THREAD_CONTROL_STACK_SIZE+
 309          BINDING_STACK_SIZE+
 310          ALIEN_STACK_SIZE);
 311
 312 #ifdef LISP_FEATURE_SB_THREAD
 313     for(i = 0; i < (dynamic_values_bytes / sizeof(lispobj)); i++)
 314         per_thread->dynamic_values[i] = NO_TLS_VALUE_MARKER_WIDETAG;
 315     if (all_threads == 0) {
 316         if(SymbolValue(FREE_TLS_INDEX,0)==UNBOUND_MARKER_WIDETAG) {
 317             SetSymbolValue
 318                 (FREE_TLS_INDEX,
 319                  /* FIXME: should be MAX_INTERRUPTS -1 ? */
 320                  make_fixnum(MAX_INTERRUPTS+
 321                              sizeof(struct thread)/sizeof(lispobj)),
 322                  0);
 323             SetSymbolValue(TLS_INDEX_LOCK,make_fixnum(0),0);
 324         }
 325 #define STATIC_TLS_INIT(sym,field) \
 326   ((struct symbol *)(sym-OTHER_POINTER_LOWTAG))->tls_index= \
 327   make_fixnum(THREAD_SLOT_OFFSET_WORDS(field))
 328
 329         STATIC_TLS_INIT(BINDING_STACK_START,binding_stack_start);
 330         STATIC_TLS_INIT(BINDING_STACK_POINTER,binding_stack_pointer);
 331         STATIC_TLS_INIT(CONTROL_STACK_START,control_stack_start);
 332         STATIC_TLS_INIT(CONTROL_STACK_END,control_stack_end);
 333         STATIC_TLS_INIT(ALIEN_STACK,alien_stack_pointer);
 334 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 335         STATIC_TLS_INIT(PSEUDO_ATOMIC_BITS,pseudo_atomic_bits);
 336 #endif
 337 #undef STATIC_TLS_INIT
 338     }
 339 #endif
 340
 341     th=&per_thread->thread;
 342     th->control_stack_start = spaces;
 343     th->binding_stack_start=
 344         (lispobj*)((void*)th->control_stack_start+THREAD_CONTROL_STACK_SIZE);
 345     th->control_stack_end = th->binding_stack_start;
 346     th->alien_stack_start=
 347         (lispobj*)((void*)th->binding_stack_start+BINDING_STACK_SIZE);
 348     th->binding_stack_pointer=th->binding_stack_start;
 349     th->this=th;
 350     th->os_thread=0;
 351     th->state=STATE_RUNNING;
 352 #ifdef LISP_FEATURE_STACK_GROWS_DOWNWARD_NOT_UPWARD
 353     th->alien_stack_pointer=((void *)th->alien_stack_start
 354                              + ALIEN_STACK_SIZE-N_WORD_BYTES);
 355 #else
 356     th->alien_stack_pointer=((void *)th->alien_stack_start);
 357 #endif
 358 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 359     th->pseudo_atomic_bits=0;
 360 #endif
 361 #ifdef LISP_FEATURE_GENCGC
 362     gc_set_region_empty(&th->alloc_region);
 363 #endif
 364
 365 #ifndef LISP_FEATURE_SB_THREAD
 366     /* the tls-points-into-struct-thread trick is only good for threaded
 367      * sbcl, because unithread sbcl doesn't have tls.  So, we copy the
 368      * appropriate values from struct thread here, and make sure that
 369      * we use the appropriate SymbolValue macros to access any of the
 370      * variable quantities from the C runtime.  It's not quite OAOOM,
 371      * it just feels like it */
 372     SetSymbolValue(BINDING_STACK_START,(lispobj)th->binding_stack_start,th);
 373     SetSymbolValue(CONTROL_STACK_START,(lispobj)th->control_stack_start,th);
 374     SetSymbolValue(CONTROL_STACK_END,(lispobj)th->control_stack_end,th);
 375 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 376     SetSymbolValue(BINDING_STACK_POINTER,(lispobj)th->binding_stack_pointer,th);
 377     SetSymbolValue(ALIEN_STACK,(lispobj)th->alien_stack_pointer,th);
 378     SetSymbolValue(PSEUDO_ATOMIC_BITS,(lispobj)th->pseudo_atomic_bits,th);
 379 #else
 380     current_binding_stack_pointer=th->binding_stack_pointer;
 381     current_control_stack_pointer=th->control_stack_start;
 382 #endif
 383 #endif
 384     bind_variable(CURRENT_CATCH_BLOCK,make_fixnum(0),th);
 385     bind_variable(CURRENT_UNWIND_PROTECT_BLOCK,make_fixnum(0),th);
 386     bind_variable(FREE_INTERRUPT_CONTEXT_INDEX,make_fixnum(0),th);
 387     bind_variable(INTERRUPT_PENDING, NIL,th);
 388     bind_variable(INTERRUPTS_ENABLED,T,th);
 389     bind_variable(GC_PENDING,NIL,th);
 390 #ifdef LISP_FEATURE_SB_THREAD
 391     bind_variable(STOP_FOR_GC_PENDING,NIL,th);
 392 #endif
 393
 394     th->interrupt_data = (struct interrupt_data *)
 395         os_validate(0,(sizeof (struct interrupt_data)));
 396     if (!th->interrupt_data) {
 397         free_thread_struct(th);
 398         return 0;
 399     }
 400     th->interrupt_data->pending_handler = 0;
 401     th->no_tls_value_marker=initial_function;
 402     return th;
 403 }
 404
 405 void create_initial_thread(lispobj initial_function) {
 406     struct thread *th=create_thread_struct(initial_function);
 407     if(th) {
 408         initial_thread_trampoline(th); /* no return */
 409     } else lose("can't create initial thread\n");
 410 }
 411
 412 #ifdef LISP_FEATURE_SB_THREAD
 413
 414 #ifndef __USE_XOPEN2K
 415 extern int pthread_attr_setstack (pthread_attr_t *__attr, void *__stackaddr,
 416                                   size_t __stacksize);
 417 #endif
 418
 419 boolean create_os_thread(struct thread *th,os_thread_t *kid_tid)
 420 {
 421     /* The new thread inherits the restrictive signal mask set here,
 422      * and enables signals again when it is set up properly. */
 423     pthread_attr_t attr;
 424     sigset_t newset,oldset;
 425     boolean r=1;
 426     int retcode, initcode, sizecode, addrcode;
 427
 428     FSHOW_SIGNAL((stderr,"/create_os_thread: creating new thread\n"));
 429
 430     sigemptyset(&newset);
 431     /* Blocking deferrable signals is enough, no need to block
 432      * SIG_STOP_FOR_GC because the child process is not linked onto
 433      * all_threads until it's ready. */
 434     sigaddset_deferrable(&newset);
 435     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 436
 437 #if defined(LISP_FEATURE_DARWIN)
 438 #define CONTROL_STACK_ADJUST 8192 /* darwin wants page-aligned stacks */
 439 #else
 440 #define CONTROL_STACK_ADJUST 16
 441 #endif
 442
 443     if((initcode = pthread_attr_init(&attr)) ||
 444        /* FIXME: why do we even have this in the first place? */
 445        (pthread_attr_setstack(&attr,th->control_stack_start,
 446                               THREAD_CONTROL_STACK_SIZE-CONTROL_STACK_ADJUST)) ||
 447 #undef CONTROL_STACK_ADJUST
 448        (retcode = pthread_create
 449         (kid_tid,&attr,(void *(*)(void *))new_thread_trampoline,th))) {
 450         FSHOW_SIGNAL((stderr, "init, size, addr = %d, %d, %d\n", initcode, sizecode, addrcode));
 451         FSHOW_SIGNAL((stderr, printf("pthread_create returned %d, errno %d\n", retcode, errno)));
 452         FSHOW_SIGNAL((stderr, "wanted stack size %d, min stack size %d\n",
 453                       THREAD_CONTROL_STACK_SIZE-16, PTHREAD_STACK_MIN));
 454         if(retcode < 0) {
 455             perror("create_os_thread");
 456         }
 457         r=0;
 458     }
 459 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 460     free_freeable_stacks();
 461 #endif
 462     thread_sigmask(SIG_SETMASK,&oldset,0);
 463     return r;
 464 }
 465
 466 os_thread_t create_thread(lispobj initial_function) {
 467     struct thread *th;
 468     os_thread_t kid_tid;
 469
 470     /* Assuming that a fresh thread struct has no lisp objects in it,
 471      * linking it to all_threads can be left to the thread itself
 472      * without fear of gc lossage. initial_function violates this
 473      * assumption and must stay pinned until the child starts up. */
 474     th = create_thread_struct(initial_function);
 475     if(th==0) return 0;
 476
 477     if (create_os_thread(th,&kid_tid)) {
 478         return kid_tid;
 479     } else {
 480         free_thread_struct(th);
 481         return 0;
 482     }
 483 }
 484
 485 /* Send the signo to os_thread, retry if the rt signal queue is
 486  * full. */
 487 static int kill_thread_safely(os_thread_t os_thread, int signo)
 488 {
 489     int r;
 490     /* The man page does not mention EAGAIN as a valid return value
 491      * for either pthread_kill or kill. But that's theory, this is
 492      * practice. By waiting here we assume that the delivery of this
 493      * signal is not necessary for the delivery of the signals in the
 494      * queue. In other words, we _assume_ there are no deadlocks. */
 495     while ((r=pthread_kill(os_thread,signo))==EAGAIN) {
 496         /* wait a bit then try again in the hope of the rt signal
 497          * queue not being full */
 498         FSHOW_SIGNAL((stderr,"/rt signal queue full\n"));
 499         /* FIXME: some kind of backoff (random, exponential) would be
 500          * nice. */
 501         sleep(1);
 502     }
 503     return r;
 504 }
 505
 506 int signal_interrupt_thread(os_thread_t os_thread)
 507 {
 508     int status = kill_thread_safely(os_thread, SIG_INTERRUPT_THREAD);
 509     if (status == 0) {
 510         return 0;
 511     } else if (status == ESRCH) {
 512         return -1;
 513     } else {
 514         lose("cannot send SIG_INTERRUPT_THREAD to thread=%lu: %d, %s\n",
 515              os_thread, status, strerror(status));
 516     }
 517 }
 518
 519 /* stopping the world is a two-stage process.  From this thread we signal
 520  * all the others with SIG_STOP_FOR_GC.  The handler for this signal does
 521  * the usual pseudo-atomic checks (we don't want to stop a thread while
 522  * it's in the middle of allocation) then waits for another SIG_STOP_FOR_GC.
 523  */
 524
 525 /* To avoid deadlocks when gc stops the world all clients of each
 526  * mutex must enable or disable SIG_STOP_FOR_GC for the duration of
 527  * holding the lock, but they must agree on which. */
 528 void gc_stop_the_world()
 529 {
 530     struct thread *p,*th=arch_os_get_current_thread();
 531     int status, lock_ret;
 532     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock, thread=%lu\n",
 533                   th->os_thread));
 534     /* keep threads from starting while the world is stopped. */
 535     lock_ret = pthread_mutex_lock(&all_threads_lock);      \
 536     gc_assert(lock_ret == 0);
 537
 538     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock, thread=%lu\n",
 539                   th->os_thread));
 540     /* stop all other threads by sending them SIG_STOP_FOR_GC */
 541     for(p=all_threads; p; p=p->next) {
 542         gc_assert(p->os_thread != 0);
 543         FSHOW_SIGNAL((stderr,"/gc_stop_the_world: p->state: %x\n", p->state));
 544         if((p!=th) && ((p->state==STATE_RUNNING))) {
 545             FSHOW_SIGNAL((stderr,"/gc_stop_the_world: suspending %x, os_thread %x\n",
 546                           p, p->os_thread));
 547             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 548             if (status==ESRCH) {
 549                 /* This thread has exited. */
 550                 gc_assert(p->state==STATE_DEAD);
 551             } else if (status) {
 552                 lose("cannot send suspend thread=%lu: %d, %s\n",
 553                      p->os_thread,status,strerror(status));
 554             }
 555         }
 556     }
 557     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:signals sent\n"));
 558     /* wait for the running threads to stop or finish */
 559     for(p=all_threads;p;) {
 560         FSHOW_SIGNAL((stderr,"/gc_stop_the_world: th: %p, p: %p\n", th, p));
 561         if((p!=th) && (p->state==STATE_RUNNING)) {
 562             sched_yield();
 563         } else {
 564             p=p->next;
 565         }
 566     }
 567     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:end\n"));
 568 }
 569
 570 void gc_start_the_world()
 571 {
 572     struct thread *p,*th=arch_os_get_current_thread();
 573     int status, lock_ret;
 574     /* if a resumed thread creates a new thread before we're done with
 575      * this loop, the new thread will get consed on the front of
 576      * all_threads, but it won't have been stopped so won't need
 577      * restarting */
 578     FSHOW_SIGNAL((stderr,"/gc_start_the_world:begin\n"));
 579     for(p=all_threads;p;p=p->next) {
 580         gc_assert(p->os_thread!=0);
 581         if((p!=th) && (p->state!=STATE_DEAD)) {
 582             if(p->state!=STATE_SUSPENDED) {
 583                 lose("gc_start_the_world: wrong thread state is %d\n",
 584                      fixnum_value(p->state));
 585             }
 586             FSHOW_SIGNAL((stderr, "/gc_start_the_world: resuming %lu\n",
 587                           p->os_thread));
 588             p->state=STATE_RUNNING;
 589
 590 #if defined(SIG_RESUME_FROM_GC)
 591             status=kill_thread_safely(p->os_thread,SIG_RESUME_FROM_GC);
 592 #else
 593             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 594 #endif
 595             if (status) {
 596                 lose("cannot resume thread=%lu: %d, %s\n",
 597                      p->os_thread,status,strerror(status));
 598             }
 599         }
 600     }
 601     /* If we waited here until all threads leave STATE_SUSPENDED, then
 602      * SIG_STOP_FOR_GC wouldn't need to be a rt signal. That has some
 603      * performance implications, but does away with the 'rt signal
 604      * queue full' problem. */
 605
 606     lock_ret = pthread_mutex_unlock(&all_threads_lock);
 607     gc_assert(lock_ret == 0);
 608
 609     FSHOW_SIGNAL((stderr,"/gc_start_the_world:end\n"));
 610 }
 611 #endif