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             SetSymbolValue(TLS_INDEX_LOCK,make_fixnum(0),0);
 184         }
 185 #define STATIC_TLS_INIT(sym,field) \
 186   ((struct symbol *)(sym-OTHER_POINTER_LOWTAG))->tls_index= \
 187   make_fixnum(THREAD_SLOT_OFFSET_WORDS(field))
 188
 189         STATIC_TLS_INIT(BINDING_STACK_START,binding_stack_start);
 190         STATIC_TLS_INIT(BINDING_STACK_POINTER,binding_stack_pointer);
 191         STATIC_TLS_INIT(CONTROL_STACK_START,control_stack_start);
 192         STATIC_TLS_INIT(CONTROL_STACK_END,control_stack_end);
 193         STATIC_TLS_INIT(ALIEN_STACK,alien_stack_pointer);
 194 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 195         STATIC_TLS_INIT(PSEUDO_ATOMIC_ATOMIC,pseudo_atomic_atomic);
 196         STATIC_TLS_INIT(PSEUDO_ATOMIC_INTERRUPTED,pseudo_atomic_interrupted);
 197 #endif
 198 #undef STATIC_TLS_INIT
 199 #endif
 200     }
 201
 202     th=&per_thread->thread;
 203     th->control_stack_start = spaces;
 204     th->binding_stack_start=
 205         (lispobj*)((void*)th->control_stack_start+THREAD_CONTROL_STACK_SIZE);
 206     th->control_stack_end = th->binding_stack_start;
 207     th->alien_stack_start=
 208         (lispobj*)((void*)th->binding_stack_start+BINDING_STACK_SIZE);
 209     th->binding_stack_pointer=th->binding_stack_start;
 210     th->this=th;
 211     th->os_thread=0;
 212     th->interrupt_fun=NIL;
 213     th->interrupt_fun_lock=0;
 214     th->state=STATE_STARTING;
 215 #ifdef LISP_FEATURE_STACK_GROWS_DOWNWARD_NOT_UPWARD
 216     th->alien_stack_pointer=((void *)th->alien_stack_start
 217                              + ALIEN_STACK_SIZE-N_WORD_BYTES);
 218 #else
 219     th->alien_stack_pointer=((void *)th->alien_stack_start);
 220 #endif
 221 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 222     th->pseudo_atomic_interrupted=0;
 223     th->pseudo_atomic_atomic=0;
 224 #endif
 225 #ifdef LISP_FEATURE_GENCGC
 226     gc_set_region_empty(&th->alloc_region);
 227 #endif
 228
 229 #ifndef LISP_FEATURE_SB_THREAD
 230     /* the tls-points-into-struct-thread trick is only good for threaded
 231      * sbcl, because unithread sbcl doesn't have tls.  So, we copy the
 232      * appropriate values from struct thread here, and make sure that
 233      * we use the appropriate SymbolValue macros to access any of the
 234      * variable quantities from the C runtime.  It's not quite OAOOM,
 235      * it just feels like it */
 236     SetSymbolValue(BINDING_STACK_START,(lispobj)th->binding_stack_start,th);
 237     SetSymbolValue(CONTROL_STACK_START,(lispobj)th->control_stack_start,th);
 238     SetSymbolValue(CONTROL_STACK_END,(lispobj)th->control_stack_end,th);
 239 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 240     SetSymbolValue(BINDING_STACK_POINTER,(lispobj)th->binding_stack_pointer,th);
 241     SetSymbolValue(ALIEN_STACK,(lispobj)th->alien_stack_pointer,th);
 242     SetSymbolValue(PSEUDO_ATOMIC_ATOMIC,(lispobj)th->pseudo_atomic_atomic,th);
 243     SetSymbolValue(PSEUDO_ATOMIC_INTERRUPTED,th->pseudo_atomic_interrupted,th);
 244 #else
 245     current_binding_stack_pointer=th->binding_stack_pointer;
 246     current_control_stack_pointer=th->control_stack_start;
 247 #endif
 248 #endif
 249     bind_variable(CURRENT_CATCH_BLOCK,make_fixnum(0),th);
 250     bind_variable(CURRENT_UNWIND_PROTECT_BLOCK,make_fixnum(0),th);
 251     bind_variable(FREE_INTERRUPT_CONTEXT_INDEX,make_fixnum(0),th);
 252     bind_variable(INTERRUPT_PENDING, NIL,th);
 253     bind_variable(INTERRUPTS_ENABLED,T,th);
 254     bind_variable(GC_PENDING,NIL,th);
 255 #ifdef LISP_FEATURE_SB_THREAD
 256     bind_variable(STOP_FOR_GC_PENDING,NIL,th);
 257 #endif
 258
 259     th->interrupt_data = (struct interrupt_data *)
 260         os_validate(0,(sizeof (struct interrupt_data)));
 261     if (!th->interrupt_data) {
 262         free_thread_struct(th);
 263         return 0;
 264     }
 265     if(all_threads)
 266         memcpy(th->interrupt_data,
 267                arch_os_get_current_thread()->interrupt_data,
 268                sizeof (struct interrupt_data));
 269     else
 270         memcpy(th->interrupt_data,global_interrupt_data,
 271                sizeof (struct interrupt_data));
 272
 273     th->no_tls_value_marker=initial_function;
 274     return th;
 275 }
 276
 277 static void
 278 link_thread(struct thread *th,os_thread_t kid_tid)
 279 {
 280     if (all_threads) all_threads->prev=th;
 281     th->next=all_threads;
 282     th->prev=0;
 283     all_threads=th;
 284     /* note that th->os_thread is 0 at this time.  We rely on
 285      * all_threads_lock to ensure that we don't have >1 thread with
 286      * os_thread=0 on the list at once
 287      */
 288     protect_control_stack_guard_page(th,1);
 289     /* child will not start until this is set */
 290     th->os_thread=kid_tid;
 291     FSHOW((stderr,"/created thread %lu\n",kid_tid));
 292 }
 293
 294 void create_initial_thread(lispobj initial_function) {
 295     struct thread *th=create_thread_struct(initial_function);
 296     os_thread_t kid_tid=thread_self();
 297     if(th && kid_tid>0) {
 298         link_thread(th,kid_tid);
 299         initial_thread_trampoline(all_threads); /* no return */
 300     } else lose("can't create initial thread");
 301 }
 302
 303 #ifdef LISP_FEATURE_SB_THREAD
 304
 305 #ifndef __USE_XOPEN2K
 306 extern int pthread_attr_setstack (pthread_attr_t *__attr, void *__stackaddr,
 307                                   size_t __stacksize);
 308 #endif
 309
 310 boolean create_os_thread(struct thread *th,os_thread_t *kid_tid)
 311 {
 312     /* The new thread inherits the restrictive signal mask set here,
 313      * and enables signals again when it is set up properly. */
 314     pthread_attr_t attr;
 315     sigset_t newset,oldset;
 316     boolean r=1;
 317     sigemptyset(&newset);
 318     /* Blocking deferrable signals is enough, since gc_stop_the_world
 319      * waits until the child leaves STATE_STARTING. And why not let gc
 320      * proceed as soon as possible? */
 321     sigaddset_deferrable(&newset);
 322     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 323
 324     if((pthread_attr_init(&attr)) ||
 325        (pthread_attr_setstack(&attr,th->control_stack_start,
 326                               THREAD_CONTROL_STACK_SIZE-16)) ||
 327        (pthread_create
 328         (kid_tid,&attr,(void *(*)(void *))new_thread_trampoline,th)))
 329         r=0;
 330     thread_sigmask(SIG_SETMASK,&oldset,0);
 331     return r;
 332 }
 333
 334 struct thread *create_thread(lispobj initial_function) {
 335     struct thread *th;
 336     os_thread_t kid_tid=0;
 337     boolean success;
 338
 339     if(linux_no_threads_p) return 0;
 340
 341     th=create_thread_struct(initial_function);
 342     if(th==0) return 0;
 343
 344     /* we must not be interrupted here after a successful
 345      * create_os_thread, because the kid will be waiting for its
 346      * thread struct to be linked */
 347     GET_ALL_THREADS_LOCK("create_thread")
 348
 349     success=create_os_thread(th,&kid_tid);
 350     if (success)
 351         link_thread(th,kid_tid);
 352     else
 353         free_thread_struct(th);
 354
 355     RELEASE_ALL_THREADS_LOCK("create_thread")
 356
 357     if (success)
 358         return th;
 359     else
 360         return 0;
 361 }
 362
 363 /* called from lisp from the thread object finalizer */
 364 void reap_dead_thread(struct thread *th)
 365 {
 366     if(th->state!=STATE_DEAD)
 367         lose("thread %p is not joinable, state=%d\n",th,th->state);
 368 #ifdef LISP_FEATURE_GENCGC
 369     {
 370         sigset_t newset,oldset;
 371         sigemptyset(&newset);
 372         sigaddset_blockable(&newset);
 373         thread_sigmask(SIG_BLOCK, &newset, &oldset);
 374         gc_alloc_update_page_tables(0, &th->alloc_region);
 375         thread_sigmask(SIG_SETMASK,&oldset,0);
 376     }
 377 #endif
 378     GET_ALL_THREADS_LOCK("reap_dead_thread")
 379     FSHOW((stderr,"/reap_dead_thread: reaping %lu\n",th->os_thread));
 380     if(th->prev)
 381         th->prev->next=th->next;
 382     else all_threads=th->next;
 383     if(th->next)
 384         th->next->prev=th->prev;
 385     RELEASE_ALL_THREADS_LOCK("reap_dead_thread")
 386     if(th->tls_cookie>=0) arch_os_thread_cleanup(th);
 387     gc_assert(pthread_join(th->os_thread,NULL)==0);
 388     free_thread_struct(th);
 389 }
 390
 391 /* Send the signo to os_thread, retry if the rt signal queue is
 392  * full. */
 393 static int kill_thread_safely(os_thread_t os_thread, int signo)
 394 {
 395     int r;
 396     /* The man page does not mention EAGAIN as a valid return value
 397      * for either pthread_kill or kill. But that's theory, this is
 398      * practice. By waiting here we assume that the delivery of this
 399      * signal is not necessary for the delivery of the signals in the
 400      * queue. In other words, we _assume_ there are no deadlocks. */
 401     while ((r=pthread_kill(os_thread,signo))==EAGAIN) {
 402         /* wait a bit then try again in the hope of the rt signal
 403          * queue not being full */
 404         FSHOW_SIGNAL((stderr,"/rt signal queue full\n"));
 405         /* FIXME: some kind of backoff (random, exponential) would be
 406          * nice. */
 407         sleep(1);
 408     }
 409     return r;
 410 }
 411
 412 int interrupt_thread(struct thread *th, lispobj function)
 413 {
 414     /* In clone_threads, if A and B both interrupt C at approximately
 415      * the same time, it does not matter: the second signal will be
 416      * masked until the handler has returned from the first one.  In
 417      * pthreads though, we can't put the knowledge of what function to
 418      * call into the siginfo, so we have to store it in the
 419      * destination thread, and do it in such a way that A won't
 420      * clobber B's interrupt.  Hence, this stupid linked list.
 421      *
 422      * This does depend on SIG_INTERRUPT_THREAD being queued (as POSIX
 423      * RT signals are): we need to keep interrupt_fun data for exactly
 424      * as many signals as are going to be received by the destination
 425      * thread.
 426      */
 427     lispobj c=alloc_cons(function,NIL);
 428     sigset_t newset,oldset;
 429     sigemptyset(&newset);
 430     /* interrupt_thread_handler locks this spinlock with blockables
 431      * blocked (it does so for the sake of
 432      * arrange_return_to_lisp_function), so we must also block them or
 433      * else SIG_STOP_FOR_GC and all_threads_lock will find a way to
 434      * deadlock. */
 435     sigaddset_blockable(&newset);
 436     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 437     if (th == arch_os_get_current_thread())
 438         lose("cannot interrupt current thread");
 439     get_spinlock(&th->interrupt_fun_lock,
 440                  (long)arch_os_get_current_thread());
 441     ((struct cons *)native_pointer(c))->cdr=th->interrupt_fun;
 442     th->interrupt_fun=c;
 443     release_spinlock(&th->interrupt_fun_lock);
 444     thread_sigmask(SIG_SETMASK,&oldset,0);
 445     /* Called from lisp with the thread object as a parameter. Thus,
 446      * the object cannot be garbage collected and consequently reaped
 447      * and joined. Because it's not joined, kill should work (even if
 448      * the thread has died/exited). */
 449     {
 450         int status=kill_thread_safely(th->os_thread,SIG_INTERRUPT_THREAD);
 451         if (status==0) {
 452             return 0;
 453         } else if (status==ESRCH) {
 454             /* This thread has exited. */
 455             th->interrupt_fun=NIL;
 456             errno=ESRCH;
 457             return -1;
 458         } else {
 459             lose("cannot send SIG_INTERRUPT_THREAD to thread=%lu: %d, %s",
 460                  th->os_thread,status,strerror(status));
 461         }
 462     }
 463 }
 464
 465 /* stopping the world is a two-stage process.  From this thread we signal
 466  * all the others with SIG_STOP_FOR_GC.  The handler for this signal does
 467  * the usual pseudo-atomic checks (we don't want to stop a thread while
 468  * it's in the middle of allocation) then waits for another SIG_STOP_FOR_GC.
 469  */
 470
 471 /* To avoid deadlocks when gc stops the world all clients of each
 472  * mutex must enable or disable SIG_STOP_FOR_GC for the duration of
 473  * holding the lock, but they must agree on which. */
 474 void gc_stop_the_world()
 475 {
 476     struct thread *p,*th=arch_os_get_current_thread();
 477     int status;
 478     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock, thread=%lu\n",
 479                   th->os_thread));
 480     /* keep threads from starting while the world is stopped. */
 481     pthread_mutex_lock(&all_threads_lock); \
 482     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock, thread=%lu\n",
 483                   th->os_thread));
 484     /* stop all other threads by sending them SIG_STOP_FOR_GC */
 485     for(p=all_threads; p; p=p->next) {
 486         while(p->state==STATE_STARTING) sched_yield();
 487         if((p!=th) && (p->state==STATE_RUNNING)) {
 488             FSHOW_SIGNAL((stderr,"/gc_stop_the_world: suspending %lu\n",
 489                           p->os_thread));
 490             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 491             if (status==ESRCH) {
 492                 /* This thread has exited. */
 493                 gc_assert(p->state==STATE_DEAD);
 494             } else if (status) {
 495                 lose("cannot send suspend thread=%lu: %d, %s",
 496                      p->os_thread,status,strerror(status));
 497             }
 498         }
 499     }
 500     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:signals sent\n"));
 501     /* wait for the running threads to stop or finish */
 502     for(p=all_threads;p;) {
 503         gc_assert(p->os_thread!=0);
 504         gc_assert(p->state!=STATE_STARTING);
 505         if((p==th) || (p->state==STATE_SUSPENDED) ||
 506            (p->state==STATE_DEAD)) {
 507             p=p->next;
 508         } else {
 509             sched_yield();
 510         }
 511     }
 512     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:end\n"));
 513 }
 514
 515 void gc_start_the_world()
 516 {
 517     struct thread *p,*th=arch_os_get_current_thread();
 518     int status;
 519     /* if a resumed thread creates a new thread before we're done with
 520      * this loop, the new thread will get consed on the front of
 521      * all_threads, but it won't have been stopped so won't need
 522      * restarting */
 523     FSHOW_SIGNAL((stderr,"/gc_start_the_world:begin\n"));
 524     for(p=all_threads;p;p=p->next) {
 525         gc_assert(p->os_thread!=0);
 526         if((p!=th) && (p->state!=STATE_DEAD)) {
 527             if(p->state!=STATE_SUSPENDED) {
 528                 lose("gc_start_the_world: wrong thread state is %d\n",
 529                      fixnum_value(p->state));
 530             }
 531             FSHOW_SIGNAL((stderr, "/gc_start_the_world: resuming %lu\n",
 532                           p->os_thread));
 533             p->state=STATE_RUNNING;
 534             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 535             if (status) {
 536                 lose("cannot resume thread=%lu: %d, %s",
 537                      p->os_thread,status,strerror(status));
 538             }
 539         }
 540     }
 541     /* If we waited here until all threads leave STATE_SUSPENDED, then
 542      * SIG_STOP_FOR_GC wouldn't need to be a rt signal. That has some
 543      * performance implications, but does away with the 'rt signal
 544      * queue full' problem. */
 545     pthread_mutex_unlock(&all_threads_lock); \
 546     FSHOW_SIGNAL((stderr,"/gc_start_the_world:end\n"));
 547 }
 548 #endif