src/runtime/thread.c

   1 #include <stdlib.h>
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <sched.h>
   5 #include <signal.h>
   6 #include <stddef.h>
   7 #include <errno.h>
   8 #include <sys/types.h>
   9 #include <sys/wait.h>
  10
  11 #include "sbcl.h"
  12 #include "runtime.h"
  13 #include "validate.h"           /* for CONTROL_STACK_SIZE etc */
  14 #include "alloc.h"
  15 #include "thread.h"
  16 #include "arch.h"
  17 #include "target-arch-os.h"
  18 #include "os.h"
  19 #include "globals.h"
  20 #include "dynbind.h"
  21 #include "genesis/cons.h"
  22 #include "genesis/fdefn.h"
  23 #include "interr.h"             /* for lose() */
  24 #include "gc-internal.h"
  25
  26 #define ALIEN_STACK_SIZE (1*1024*1024) /* 1Mb size chosen at random */
  27
  28 int dynamic_values_bytes=4096*sizeof(lispobj);  /* same for all threads */
  29 struct thread * volatile all_threads;
  30 extern struct interrupt_data * global_interrupt_data;
  31 extern int linux_no_threads_p;
  32
  33 #ifdef LISP_FEATURE_SB_THREAD
  34
  35 pthread_mutex_t all_threads_lock = PTHREAD_MUTEX_INITIALIZER;
  36
  37 /* When trying to get all_threads_lock one should make sure that
  38  * sig_stop_for_gc is not blocked. Else there would be a possible
  39  * deadlock: gc locks it, other thread blocks signals, gc sends stop
  40  * request to other thread and waits, other thread blocks on lock. */
  41 void check_sig_stop_for_gc_can_arrive_or_lose()
  42 {
  43     /* Get the current sigmask, by blocking the empty set. */
  44     sigset_t empty,current;
  45     sigemptyset(&empty);
  46     thread_sigmask(SIG_BLOCK, &empty, &current);
  47     if (sigismember(&current,SIG_STOP_FOR_GC))
  48         lose("SIG_STOP_FOR_GC cannot arrive: it is blocked\n");
  49     if (SymbolValue(GC_INHIBIT,arch_os_get_current_thread()) != NIL)
  50         lose("SIG_STOP_FOR_GC cannot arrive: gc is inhibited\n");
  51     if (arch_pseudo_atomic_atomic(NULL))
  52         lose("SIG_STOP_FOR_GC cannot arrive: in pseudo atomic\n");
  53 }
  54
  55 #define GET_ALL_THREADS_LOCK(name) \
  56     { \
  57         sigset_t _newset,_oldset; \
  58         sigemptyset(&_newset); \
  59         sigaddset_deferrable(&_newset); \
  60         thread_sigmask(SIG_BLOCK, &_newset, &_oldset); \
  61         check_sig_stop_for_gc_can_arrive_or_lose(); \
  62         FSHOW_SIGNAL((stderr,"/%s:waiting on lock=%ld, thread=%lu\n",name, \
  63                all_threads_lock,arch_os_get_current_thread()->os_thread)); \
  64         pthread_mutex_lock(&all_threads_lock); \
  65         FSHOW_SIGNAL((stderr,"/%s:got lock, thread=%lu\n", \
  66                name,arch_os_get_current_thread()->os_thread));
  67
  68 #define RELEASE_ALL_THREADS_LOCK(name) \
  69         FSHOW_SIGNAL((stderr,"/%s:released lock\n",name)); \
  70         pthread_mutex_unlock(&all_threads_lock); \
  71         thread_sigmask(SIG_SETMASK,&_oldset,0); \
  72     }
  73 #endif
  74
  75
  76 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
  77 extern lispobj call_into_lisp_first_time(lispobj fun, lispobj *args, int nargs);
  78 #endif
  79
  80 static int
  81 initial_thread_trampoline(struct thread *th)
  82 {
  83     lispobj function;
  84 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
  85     lispobj *args = NULL;
  86 #endif
  87     function = th->no_tls_value_marker;
  88     th->no_tls_value_marker = NO_TLS_VALUE_MARKER_WIDETAG;
  89     if(arch_os_thread_init(th)==0) return 1;
  90
  91     if(th->os_thread < 1) lose("th->os_thread not set up right");
  92     th->state=STATE_RUNNING;
  93 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
  94     return call_into_lisp_first_time(function,args,0);
  95 #else
  96     return funcall0(function);
  97 #endif
  98 }
  99
 100 #ifdef LISP_FEATURE_SB_THREAD
 101
 102 /* this is the first thing that runs in the child (which is why the
 103  * silly calling convention).  Basically it calls the user's requested
 104  * lisp function after doing arch_os_thread_init and whatever other
 105  * bookkeeping needs to be done
 106  */
 107 int
 108 new_thread_trampoline(struct thread *th)
 109 {
 110     lispobj function;
 111     int result;
 112     function = th->no_tls_value_marker;
 113     th->no_tls_value_marker = NO_TLS_VALUE_MARKER_WIDETAG;
 114     if(arch_os_thread_init(th)==0) {
 115         /* FIXME: handle error */
 116         lose("arch_os_thread_init failed\n");
 117     }
 118
 119     /* wait here until our thread is linked into all_threads: see below */
 120     {
 121         volatile os_thread_t *tid=&th->os_thread;
 122         while(*tid<1) sched_yield();
 123     }
 124
 125     th->state=STATE_RUNNING;
 126     result = funcall0(function);
 127     th->state=STATE_DEAD;
 128     return result;
 129 }
 130 #endif /* LISP_FEATURE_SB_THREAD */
 131
 132 #define THREAD_STRUCT_SIZE (THREAD_CONTROL_STACK_SIZE + BINDING_STACK_SIZE + \
 133                             ALIEN_STACK_SIZE + dynamic_values_bytes + \
 134                             32 * SIGSTKSZ)
 135
 136 static void
 137 free_thread_struct(struct thread *th)
 138 {
 139     if (th->interrupt_data)
 140         os_invalidate((os_vm_address_t) th->interrupt_data,
 141                       (sizeof (struct interrupt_data)));
 142     os_invalidate((os_vm_address_t) th->control_stack_start,
 143                   THREAD_STRUCT_SIZE);
 144 }
 145
 146 /* this is called from any other thread to create the new one, and
 147  * initialize all parts of it that can be initialized from another
 148  * thread
 149  */
 150
 151 static struct thread *
 152 create_thread_struct(lispobj initial_function) {
 153     union per_thread_data *per_thread;
 154     struct thread *th=0;        /*  subdue gcc */
 155     void *spaces=0;
 156
 157     /* may as well allocate all the spaces at once: it saves us from
 158      * having to decide what to do if only some of the allocations
 159      * succeed */
 160     spaces=os_validate(0, THREAD_STRUCT_SIZE);
 161     if(!spaces)
 162          return NULL;
 163     per_thread=(union per_thread_data *)
 164         (spaces+
 165          THREAD_CONTROL_STACK_SIZE+
 166          BINDING_STACK_SIZE+
 167          ALIEN_STACK_SIZE);
 168
 169     if(all_threads) {
 170         memcpy(per_thread,arch_os_get_current_thread(),
 171                dynamic_values_bytes);
 172     } else {
 173 #ifdef LISP_FEATURE_SB_THREAD
 174         int i;
 175         for(i=0;i<(dynamic_values_bytes/sizeof(lispobj));i++)
 176             per_thread->dynamic_values[i]=NO_TLS_VALUE_MARKER_WIDETAG;
 177         if(SymbolValue(FREE_TLS_INDEX,0)==UNBOUND_MARKER_WIDETAG)
 178             SetSymbolValue
 179                 (FREE_TLS_INDEX,
 180                  make_fixnum(MAX_INTERRUPTS+
 181                              sizeof(struct thread)/sizeof(lispobj)),
 182                  0);
 183 #define STATIC_TLS_INIT(sym,field) \
 184   ((struct symbol *)(sym-OTHER_POINTER_LOWTAG))->tls_index= \
 185   make_fixnum(THREAD_SLOT_OFFSET_WORDS(field))
 186
 187         STATIC_TLS_INIT(BINDING_STACK_START,binding_stack_start);
 188         STATIC_TLS_INIT(BINDING_STACK_POINTER,binding_stack_pointer);
 189         STATIC_TLS_INIT(CONTROL_STACK_START,control_stack_start);
 190         STATIC_TLS_INIT(CONTROL_STACK_END,control_stack_end);
 191         STATIC_TLS_INIT(ALIEN_STACK,alien_stack_pointer);
 192 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 193         STATIC_TLS_INIT(PSEUDO_ATOMIC_ATOMIC,pseudo_atomic_atomic);
 194         STATIC_TLS_INIT(PSEUDO_ATOMIC_INTERRUPTED,pseudo_atomic_interrupted);
 195 #endif
 196 #undef STATIC_TLS_INIT
 197 #endif
 198     }
 199
 200     th=&per_thread->thread;
 201     th->control_stack_start = spaces;
 202     th->binding_stack_start=
 203         (lispobj*)((void*)th->control_stack_start+THREAD_CONTROL_STACK_SIZE);
 204     th->control_stack_end = th->binding_stack_start;
 205     th->alien_stack_start=
 206         (lispobj*)((void*)th->binding_stack_start+BINDING_STACK_SIZE);
 207     th->binding_stack_pointer=th->binding_stack_start;
 208     th->this=th;
 209     th->os_thread=0;
 210     th->interrupt_fun=NIL;
 211     th->interrupt_fun_lock=0;
 212     th->state=STATE_STARTING;
 213 #ifdef LISP_FEATURE_STACK_GROWS_DOWNWARD_NOT_UPWARD
 214     th->alien_stack_pointer=((void *)th->alien_stack_start
 215                              + ALIEN_STACK_SIZE-N_WORD_BYTES);
 216 #else
 217     th->alien_stack_pointer=((void *)th->alien_stack_start);
 218 #endif
 219 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 220     th->pseudo_atomic_interrupted=0;
 221     th->pseudo_atomic_atomic=0;
 222 #endif
 223 #ifdef LISP_FEATURE_GENCGC
 224     gc_set_region_empty(&th->alloc_region);
 225 #endif
 226
 227 #ifndef LISP_FEATURE_SB_THREAD
 228     /* the tls-points-into-struct-thread trick is only good for threaded
 229      * sbcl, because unithread sbcl doesn't have tls.  So, we copy the
 230      * appropriate values from struct thread here, and make sure that
 231      * we use the appropriate SymbolValue macros to access any of the
 232      * variable quantities from the C runtime.  It's not quite OAOOM,
 233      * it just feels like it */
 234     SetSymbolValue(BINDING_STACK_START,(lispobj)th->binding_stack_start,th);
 235     SetSymbolValue(CONTROL_STACK_START,(lispobj)th->control_stack_start,th);
 236     SetSymbolValue(CONTROL_STACK_END,(lispobj)th->control_stack_end,th);
 237 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 238     SetSymbolValue(BINDING_STACK_POINTER,(lispobj)th->binding_stack_pointer,th);
 239     SetSymbolValue(ALIEN_STACK,(lispobj)th->alien_stack_pointer,th);
 240     SetSymbolValue(PSEUDO_ATOMIC_ATOMIC,(lispobj)th->pseudo_atomic_atomic,th);
 241     SetSymbolValue(PSEUDO_ATOMIC_INTERRUPTED,th->pseudo_atomic_interrupted,th);
 242 #else
 243     current_binding_stack_pointer=th->binding_stack_pointer;
 244     current_control_stack_pointer=th->control_stack_start;
 245 #endif
 246 #endif
 247     bind_variable(CURRENT_CATCH_BLOCK,make_fixnum(0),th);
 248     bind_variable(CURRENT_UNWIND_PROTECT_BLOCK,make_fixnum(0),th);
 249     bind_variable(FREE_INTERRUPT_CONTEXT_INDEX,make_fixnum(0),th);
 250     bind_variable(INTERRUPT_PENDING, NIL,th);
 251     bind_variable(INTERRUPTS_ENABLED,T,th);
 252     bind_variable(GC_PENDING,NIL,th);
 253 #ifdef LISP_FEATURE_SB_THREAD
 254     bind_variable(STOP_FOR_GC_PENDING,NIL,th);
 255 #endif
 256
 257     th->interrupt_data = (struct interrupt_data *)
 258         os_validate(0,(sizeof (struct interrupt_data)));
 259     if (!th->interrupt_data) {
 260         free_thread_struct(th);
 261         return 0;
 262     }
 263     if(all_threads)
 264         memcpy(th->interrupt_data,
 265                arch_os_get_current_thread()->interrupt_data,
 266                sizeof (struct interrupt_data));
 267     else
 268         memcpy(th->interrupt_data,global_interrupt_data,
 269                sizeof (struct interrupt_data));
 270
 271     th->no_tls_value_marker=initial_function;
 272     return th;
 273 }
 274
 275 static void
 276 link_thread(struct thread *th,os_thread_t kid_tid)
 277 {
 278     if (all_threads) all_threads->prev=th;
 279     th->next=all_threads;
 280     th->prev=0;
 281     all_threads=th;
 282     /* note that th->os_thread is 0 at this time.  We rely on
 283      * all_threads_lock to ensure that we don't have >1 thread with
 284      * os_thread=0 on the list at once
 285      */
 286     protect_control_stack_guard_page(th,1);
 287     /* child will not start until this is set */
 288     th->os_thread=kid_tid;
 289     FSHOW((stderr,"/created thread %lu\n",kid_tid));
 290 }
 291
 292 void create_initial_thread(lispobj initial_function) {
 293     struct thread *th=create_thread_struct(initial_function);
 294     os_thread_t kid_tid=thread_self();
 295     if(th && kid_tid>0) {
 296         link_thread(th,kid_tid);
 297         initial_thread_trampoline(all_threads); /* no return */
 298     } else lose("can't create initial thread");
 299 }
 300
 301 #ifdef LISP_FEATURE_SB_THREAD
 302
 303 #ifndef __USE_XOPEN2K
 304 extern int pthread_attr_setstack (pthread_attr_t *__attr, void *__stackaddr,
 305                                   size_t __stacksize);
 306 #endif
 307
 308 boolean create_os_thread(struct thread *th,os_thread_t *kid_tid)
 309 {
 310     /* The new thread inherits the restrictive signal mask set here,
 311      * and enables signals again when it is set up properly. */
 312     pthread_attr_t attr;
 313     sigset_t newset,oldset;
 314     boolean r=1;
 315     sigemptyset(&newset);
 316     /* Blocking deferrable signals is enough, since gc_stop_the_world
 317      * waits until the child leaves STATE_STARTING. And why not let gc
 318      * proceed as soon as possible? */
 319     sigaddset_deferrable(&newset);
 320     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 321
 322     if((pthread_attr_init(&attr)) ||
 323        (pthread_attr_setstack(&attr,th->control_stack_start,
 324                               THREAD_CONTROL_STACK_SIZE-16)) ||
 325        (pthread_create
 326         (kid_tid,&attr,(void *(*)(void *))new_thread_trampoline,th)))
 327         r=0;
 328     thread_sigmask(SIG_SETMASK,&oldset,0);
 329     return r;
 330 }
 331
 332 struct thread *create_thread(lispobj initial_function) {
 333     struct thread *th;
 334     os_thread_t kid_tid=0;
 335     boolean success;
 336
 337     if(linux_no_threads_p) return 0;
 338
 339     th=create_thread_struct(initial_function);
 340     if(th==0) return 0;
 341
 342     /* we must not be interrupted here after a successful
 343      * create_os_thread, because the kid will be waiting for its
 344      * thread struct to be linked */
 345     GET_ALL_THREADS_LOCK("create_thread")
 346
 347     success=create_os_thread(th,&kid_tid);
 348     if (success)
 349         link_thread(th,kid_tid);
 350     else
 351         free_thread_struct(th);
 352
 353     RELEASE_ALL_THREADS_LOCK("create_thread")
 354
 355     if (success)
 356         return th;
 357     else
 358         return 0;
 359 }
 360
 361 /* called from lisp from the thread object finalizer */
 362 void reap_dead_thread(struct thread *th)
 363 {
 364     if(th->state!=STATE_DEAD)
 365         lose("thread %p is not joinable, state=%d\n",th,th->state);
 366 #ifdef LISP_FEATURE_GENCGC
 367     {
 368         sigset_t newset,oldset;
 369         sigemptyset(&newset);
 370         sigaddset_blockable(&newset);
 371         thread_sigmask(SIG_BLOCK, &newset, &oldset);
 372         gc_alloc_update_page_tables(0, &th->alloc_region);
 373         thread_sigmask(SIG_SETMASK,&oldset,0);
 374     }
 375 #endif
 376     GET_ALL_THREADS_LOCK("reap_dead_thread")
 377     FSHOW((stderr,"/reap_dead_thread: reaping %lu\n",th->os_thread));
 378     if(th->prev)
 379         th->prev->next=th->next;
 380     else all_threads=th->next;
 381     if(th->next)
 382         th->next->prev=th->prev;
 383     RELEASE_ALL_THREADS_LOCK("reap_dead_thread")
 384     if(th->tls_cookie>=0) arch_os_thread_cleanup(th);
 385     gc_assert(pthread_join(th->os_thread,NULL)==0);
 386     free_thread_struct(th);
 387 }
 388
 389 /* Send the signo to os_thread, retry if the rt signal queue is
 390  * full. */
 391 static int kill_thread_safely(os_thread_t os_thread, int signo)
 392 {
 393     int r;
 394     /* The man page does not mention EAGAIN as a valid return value
 395      * for either pthread_kill or kill. But that's theory, this is
 396      * practice. By waiting here we assume that the delivery of this
 397      * signal is not necessary for the delivery of the signals in the
 398      * queue. In other words, we _assume_ there are no deadlocks. */
 399     while ((r=pthread_kill(os_thread,signo))==EAGAIN) {
 400         /* wait a bit then try again in the hope of the rt signal
 401          * queue not being full */
 402         FSHOW_SIGNAL((stderr,"/rt signal queue full\n"));
 403         /* FIXME: some kind of backoff (random, exponential) would be
 404          * nice. */
 405         sleep(1);
 406     }
 407     return r;
 408 }
 409
 410 int interrupt_thread(struct thread *th, lispobj function)
 411 {
 412     /* In clone_threads, if A and B both interrupt C at approximately
 413      * the same time, it does not matter: the second signal will be
 414      * masked until the handler has returned from the first one.  In
 415      * pthreads though, we can't put the knowledge of what function to
 416      * call into the siginfo, so we have to store it in the
 417      * destination thread, and do it in such a way that A won't
 418      * clobber B's interrupt.  Hence, this stupid linked list.
 419      *
 420      * This does depend on SIG_INTERRUPT_THREAD being queued (as POSIX
 421      * RT signals are): we need to keep interrupt_fun data for exactly
 422      * as many signals as are going to be received by the destination
 423      * thread.
 424      */
 425     lispobj c=alloc_cons(function,NIL);
 426     sigset_t newset,oldset;
 427     sigemptyset(&newset);
 428     /* interrupt_thread_handler locks this spinlock with blockables
 429      * blocked (it does so for the sake of
 430      * arrange_return_to_lisp_function), so we must also block them or
 431      * else SIG_STOP_FOR_GC and all_threads_lock will find a way to
 432      * deadlock. */
 433     sigaddset_blockable(&newset);
 434     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 435     if (th == arch_os_get_current_thread())
 436         lose("cannot interrupt current thread");
 437     get_spinlock(&th->interrupt_fun_lock,
 438                  (long)arch_os_get_current_thread());
 439     ((struct cons *)native_pointer(c))->cdr=th->interrupt_fun;
 440     th->interrupt_fun=c;
 441     release_spinlock(&th->interrupt_fun_lock);
 442     thread_sigmask(SIG_SETMASK,&oldset,0);
 443     /* Called from lisp with the thread object as a parameter. Thus,
 444      * the object cannot be garbage collected and consequently reaped
 445      * and joined. Because it's not joined, kill should work (even if
 446      * the thread has died/exited). */
 447     {
 448         int status=kill_thread_safely(th->os_thread,SIG_INTERRUPT_THREAD);
 449         if (status==0) {
 450             return 0;
 451         } else if (status==ESRCH) {
 452             /* This thread has exited. */
 453             th->interrupt_fun=NIL;
 454             errno=ESRCH;
 455             return -1;
 456         } else {
 457             lose("cannot send SIG_INTERRUPT_THREAD to thread=%lu: %d, %s",
 458                  th->os_thread,status,strerror(status));
 459         }
 460     }
 461 }
 462
 463 /* stopping the world is a two-stage process.  From this thread we signal
 464  * all the others with SIG_STOP_FOR_GC.  The handler for this signal does
 465  * the usual pseudo-atomic checks (we don't want to stop a thread while
 466  * it's in the middle of allocation) then waits for another SIG_STOP_FOR_GC.
 467  */
 468
 469 /* To avoid deadlocks when gc stops the world all clients of each
 470  * mutex must enable or disable SIG_STOP_FOR_GC for the duration of
 471  * holding the lock, but they must agree on which. */
 472 void gc_stop_the_world()
 473 {
 474     struct thread *p,*th=arch_os_get_current_thread();
 475     int status;
 476     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock, thread=%lu\n",
 477                   th->os_thread));
 478     /* keep threads from starting while the world is stopped. */
 479     pthread_mutex_lock(&all_threads_lock); \
 480     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock, thread=%lu\n",
 481                   th->os_thread));
 482     /* stop all other threads by sending them SIG_STOP_FOR_GC */
 483     for(p=all_threads; p; p=p->next) {
 484         while(p->state==STATE_STARTING) sched_yield();
 485         if((p!=th) && (p->state==STATE_RUNNING)) {
 486             FSHOW_SIGNAL((stderr,"/gc_stop_the_world: suspending %lu\n",
 487                           p->os_thread));
 488             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 489             if (status==ESRCH) {
 490                 /* This thread has exited. */
 491                 gc_assert(p->state==STATE_DEAD);
 492             } else if (status) {
 493                 lose("cannot send suspend thread=%lu: %d, %s",
 494                      p->os_thread,status,strerror(status));
 495             }
 496         }
 497     }
 498     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:signals sent\n"));
 499     /* wait for the running threads to stop or finish */
 500     for(p=all_threads;p;) {
 501         gc_assert(p->os_thread!=0);
 502         gc_assert(p->state!=STATE_STARTING);
 503         if((p==th) || (p->state==STATE_SUSPENDED) ||
 504            (p->state==STATE_DEAD)) {
 505             p=p->next;
 506         } else {
 507             sched_yield();
 508         }
 509     }
 510     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:end\n"));
 511 }
 512
 513 void gc_start_the_world()
 514 {
 515     struct thread *p,*th=arch_os_get_current_thread();
 516     int status;
 517     /* if a resumed thread creates a new thread before we're done with
 518      * this loop, the new thread will get consed on the front of
 519      * all_threads, but it won't have been stopped so won't need
 520      * restarting */
 521     FSHOW_SIGNAL((stderr,"/gc_start_the_world:begin\n"));
 522     for(p=all_threads;p;p=p->next) {
 523         gc_assert(p->os_thread!=0);
 524         if((p!=th) && (p->state!=STATE_DEAD)) {
 525             if(p->state!=STATE_SUSPENDED) {
 526                 lose("gc_start_the_world: wrong thread state is %d\n",
 527                      fixnum_value(p->state));
 528             }
 529             FSHOW_SIGNAL((stderr, "/gc_start_the_world: resuming %lu\n",
 530                           p->os_thread));
 531             p->state=STATE_RUNNING;
 532             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 533             if (status) {
 534                 lose("cannot resume thread=%lu: %d, %s",
 535                      p->os_thread,status,strerror(status));
 536             }
 537         }
 538     }
 539     /* If we waited here until all threads leave STATE_SUSPENDED, then
 540      * SIG_STOP_FOR_GC wouldn't need to be a rt signal. That has some
 541      * performance implications, but does away with the 'rt signal
 542      * queue full' problem. */
 543     pthread_mutex_unlock(&all_threads_lock); \
 544     FSHOW_SIGNAL((stderr,"/gc_start_the_world:end\n"));
 545 }
 546 #endif