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 #ifdef LISP_FEATURE_FREEBSD
  55 #define CREATE_CLEANUP_THREAD
  56 #define LOCK_CREATE_THREAD
  57 #endif
  58
  59 #define ALIEN_STACK_SIZE (1*1024*1024) /* 1Mb size chosen at random */
  60
  61 struct freeable_stack {
  62 #ifdef QUEUE_FREEABLE_THREAD_STACKS
  63     struct freeable_stack *next;
  64 #endif
  65     os_thread_t os_thread;
  66     os_vm_address_t stack;
  67 };
  68
  69
  70 #ifdef QUEUE_FREEABLE_THREAD_STACKS
  71 static struct freeable_stack * volatile freeable_stack_queue = 0;
  72 static int freeable_stack_count = 0;
  73 pthread_mutex_t freeable_stack_lock = PTHREAD_MUTEX_INITIALIZER;
  74 #else
  75 static struct freeable_stack * volatile freeable_stack = 0;
  76 #endif
  77
  78 int dynamic_values_bytes=4096*sizeof(lispobj);  /* same for all threads */
  79 struct thread * volatile all_threads;
  80 extern struct interrupt_data * global_interrupt_data;
  81
  82 #ifdef LISP_FEATURE_SB_THREAD
  83 pthread_mutex_t all_threads_lock = PTHREAD_MUTEX_INITIALIZER;
  84 #ifdef LOCK_CREATE_THREAD
  85 static pthread_mutex_t create_thread_lock = PTHREAD_MUTEX_INITIALIZER;
  86 #endif
  87 #endif
  88
  89 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
  90 extern lispobj call_into_lisp_first_time(lispobj fun, lispobj *args, int nargs);
  91 #endif
  92
  93 static void
  94 link_thread(struct thread *th)
  95 {
  96     if (all_threads) all_threads->prev=th;
  97     th->next=all_threads;
  98     th->prev=0;
  99     all_threads=th;
 100 }
 101
 102 #ifdef LISP_FEATURE_SB_THREAD
 103 static void
 104 unlink_thread(struct thread *th)
 105 {
 106     if (th->prev)
 107         th->prev->next = th->next;
 108     else
 109         all_threads = th->next;
 110     if (th->next)
 111         th->next->prev = th->prev;
 112 }
 113 #endif
 114
 115 static int
 116 initial_thread_trampoline(struct thread *th)
 117 {
 118     lispobj function;
 119 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
 120     lispobj *args = NULL;
 121 #endif
 122     function = th->no_tls_value_marker;
 123     th->no_tls_value_marker = NO_TLS_VALUE_MARKER_WIDETAG;
 124     if(arch_os_thread_init(th)==0) return 1;
 125     link_thread(th);
 126     th->os_thread=thread_self();
 127 #ifndef LISP_FEATURE_WIN32
 128     protect_control_stack_guard_page(1);
 129 #endif
 130
 131 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
 132     return call_into_lisp_first_time(function,args,0);
 133 #else
 134     return funcall0(function);
 135 #endif
 136 }
 137
 138 #define THREAD_STRUCT_SIZE (THREAD_CONTROL_STACK_SIZE + BINDING_STACK_SIZE + \
 139                             ALIEN_STACK_SIZE + dynamic_values_bytes + \
 140                             32 * SIGSTKSZ)
 141
 142 #ifdef LISP_FEATURE_SB_THREAD
 143
 144 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 145
 146 queue_freeable_thread_stack(struct thread *thread_to_be_cleaned_up)
 147 {
 148      if (thread_to_be_cleaned_up) {
 149         pthread_mutex_lock(&freeable_stack_lock);
 150         if (freeable_stack_queue) {
 151             struct freeable_stack *new_freeable_stack = 0, *next;
 152             next = freeable_stack_queue;
 153             while (next->next) {
 154                 next = next->next;
 155             }
 156             new_freeable_stack = (struct freeable_stack *)
 157                 os_validate(0, sizeof(struct freeable_stack));
 158             new_freeable_stack->next = NULL;
 159             new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
 160             new_freeable_stack->stack = (os_vm_address_t)
 161                 thread_to_be_cleaned_up->control_stack_start;
 162             next->next = new_freeable_stack;
 163             freeable_stack_count++;
 164         } else {
 165             struct freeable_stack *new_freeable_stack = 0;
 166             new_freeable_stack = (struct freeable_stack *)
 167                 os_validate(0, sizeof(struct freeable_stack));
 168             new_freeable_stack->next = NULL;
 169             new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
 170             new_freeable_stack->stack = (os_vm_address_t)
 171                 thread_to_be_cleaned_up->control_stack_start;
 172             freeable_stack_queue = new_freeable_stack;
 173             freeable_stack_count++;
 174         }
 175         pthread_mutex_unlock(&freeable_stack_lock);
 176     }
 177 }
 178
 179 #define FREEABLE_STACK_QUEUE_SIZE 4
 180
 181 static void
 182 free_freeable_stacks() {
 183     if (freeable_stack_queue && (freeable_stack_count > FREEABLE_STACK_QUEUE_SIZE)) {
 184         struct freeable_stack* old;
 185         pthread_mutex_lock(&freeable_stack_lock);
 186         old = freeable_stack_queue;
 187         freeable_stack_queue = old->next;
 188         freeable_stack_count--;
 189         gc_assert(pthread_join(old->os_thread, NULL) == 0);
 190         FSHOW((stderr, "freeing thread %x stack\n", old->os_thread));
 191         os_invalidate(old->stack, THREAD_STRUCT_SIZE);
 192         os_invalidate((os_vm_address_t)old, sizeof(struct freeable_stack));
 193         pthread_mutex_unlock(&freeable_stack_lock);
 194     }
 195 }
 196
 197 #elif defined(CREATE_CLEANUP_THREAD)
 198 static void *
 199 cleanup_thread(void *arg)
 200 {
 201     struct freeable_stack *freeable = arg;
 202     pthread_t self = pthread_self();
 203
 204     FSHOW((stderr, "/cleaner thread(%p): joining %p\n",
 205            self, freeable->os_thread));
 206     gc_assert(pthread_join(freeable->os_thread, NULL) == 0);
 207     FSHOW((stderr, "/cleaner thread(%p): free stack %p\n",
 208            self, freeable->stack));
 209     os_invalidate(freeable->stack, THREAD_STRUCT_SIZE);
 210     free(freeable);
 211
 212     pthread_detach(self);
 213
 214     return NULL;
 215 }
 216
 217 static void
 218 create_cleanup_thread(struct thread *thread_to_be_cleaned_up)
 219 {
 220     pthread_t thread;
 221     int result;
 222
 223     if (thread_to_be_cleaned_up) {
 224         struct freeable_stack *freeable =
 225             malloc(sizeof(struct freeable_stack));
 226         gc_assert(freeable != NULL);
 227         freeable->os_thread = thread_to_be_cleaned_up->os_thread;
 228         freeable->stack =
 229             (os_vm_address_t) thread_to_be_cleaned_up->control_stack_start;
 230         result = pthread_create(&thread, NULL, cleanup_thread, freeable);
 231         gc_assert(result == 0);
 232         sched_yield();
 233     }
 234 }
 235
 236 #else
 237 static void
 238 free_thread_stack_later(struct thread *thread_to_be_cleaned_up)
 239 {
 240     struct freeable_stack *new_freeable_stack = 0;
 241     if (thread_to_be_cleaned_up) {
 242         new_freeable_stack = (struct freeable_stack *)
 243             os_validate(0, sizeof(struct freeable_stack));
 244         new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
 245         new_freeable_stack->stack = (os_vm_address_t)
 246             thread_to_be_cleaned_up->control_stack_start;
 247     }
 248     new_freeable_stack = (struct freeable_stack *)
 249         swap_lispobjs((lispobj *)(void *)&freeable_stack,
 250                       (lispobj)new_freeable_stack);
 251     if (new_freeable_stack) {
 252         FSHOW((stderr,"/reaping %p\n", (void*) new_freeable_stack->os_thread));
 253         /* Under NPTL pthread_join really waits until the thread
 254          * exists and the stack can be safely freed. This is sadly not
 255          * mandated by the pthread spec. */
 256         gc_assert(pthread_join(new_freeable_stack->os_thread, NULL) == 0);
 257         os_invalidate(new_freeable_stack->stack, THREAD_STRUCT_SIZE);
 258         os_invalidate((os_vm_address_t) new_freeable_stack,
 259                       sizeof(struct freeable_stack));
 260     }
 261 }
 262 #endif
 263
 264 /* this is the first thing that runs in the child (which is why the
 265  * silly calling convention).  Basically it calls the user's requested
 266  * lisp function after doing arch_os_thread_init and whatever other
 267  * bookkeeping needs to be done
 268  */
 269 int
 270 new_thread_trampoline(struct thread *th)
 271 {
 272     lispobj function;
 273     int result, lock_ret;
 274
 275     FSHOW((stderr,"/creating thread %lu\n", thread_self()));
 276     function = th->no_tls_value_marker;
 277     th->no_tls_value_marker = NO_TLS_VALUE_MARKER_WIDETAG;
 278     if(arch_os_thread_init(th)==0) {
 279         /* FIXME: handle error */
 280         lose("arch_os_thread_init failed\n");
 281     }
 282
 283     th->os_thread=thread_self();
 284     protect_control_stack_guard_page(1);
 285     /* Since GC can only know about this thread from the all_threads
 286      * list and we're just adding this thread to it there is no danger
 287      * of deadlocking even with SIG_STOP_FOR_GC blocked (which it is
 288      * not). */
 289     lock_ret = pthread_mutex_lock(&all_threads_lock);
 290     gc_assert(lock_ret == 0);
 291     link_thread(th);
 292     lock_ret = pthread_mutex_unlock(&all_threads_lock);
 293     gc_assert(lock_ret == 0);
 294
 295     result = funcall0(function);
 296
 297     /* Block GC */
 298     block_blockable_signals();
 299     th->state=STATE_DEAD;
 300
 301     /* SIG_STOP_FOR_GC is blocked and GC might be waiting for this
 302      * thread, but since we are already dead it won't wait long. */
 303     lock_ret = pthread_mutex_lock(&all_threads_lock);
 304     gc_assert(lock_ret == 0);
 305
 306     gc_alloc_update_page_tables(0, &th->alloc_region);
 307     unlink_thread(th);
 308     pthread_mutex_unlock(&all_threads_lock);
 309     gc_assert(lock_ret == 0);
 310
 311     if(th->tls_cookie>=0) arch_os_thread_cleanup(th);
 312     os_invalidate((os_vm_address_t)th->interrupt_data,
 313                   (sizeof (struct interrupt_data)));
 314
 315 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 316     queue_freeable_thread_stack(th);
 317 #elif defined(CREATE_CLEANUP_THREAD)
 318     create_cleanup_thread(th);
 319 #else
 320     free_thread_stack_later(th);
 321 #endif
 322
 323     FSHOW((stderr,"/exiting thread %p\n", thread_self()));
 324     return result;
 325 }
 326
 327 #endif /* LISP_FEATURE_SB_THREAD */
 328
 329 static void
 330 free_thread_struct(struct thread *th)
 331 {
 332     if (th->interrupt_data)
 333         os_invalidate((os_vm_address_t) th->interrupt_data,
 334                       (sizeof (struct interrupt_data)));
 335     os_invalidate((os_vm_address_t) th->control_stack_start,
 336                   THREAD_STRUCT_SIZE);
 337 }
 338
 339 /* this is called from any other thread to create the new one, and
 340  * initialize all parts of it that can be initialized from another
 341  * thread
 342  */
 343
 344 static struct thread *
 345 create_thread_struct(lispobj initial_function) {
 346     union per_thread_data *per_thread;
 347     struct thread *th=0;        /*  subdue gcc */
 348     void *spaces=0;
 349 #ifdef LISP_FEATURE_SB_THREAD
 350     int i;
 351 #endif
 352
 353 #ifdef CREATE_CLEANUP_THREAD
 354     /* Give a chance for cleanup threads to run. */
 355     sched_yield();
 356 #endif
 357     /* may as well allocate all the spaces at once: it saves us from
 358      * having to decide what to do if only some of the allocations
 359      * succeed */
 360     spaces=os_validate(0, THREAD_STRUCT_SIZE);
 361     if(!spaces)
 362          return NULL;
 363     per_thread=(union per_thread_data *)
 364         (spaces+
 365          THREAD_CONTROL_STACK_SIZE+
 366          BINDING_STACK_SIZE+
 367          ALIEN_STACK_SIZE);
 368
 369 #ifdef LISP_FEATURE_SB_THREAD
 370     for(i = 0; i < (dynamic_values_bytes / sizeof(lispobj)); i++)
 371         per_thread->dynamic_values[i] = NO_TLS_VALUE_MARKER_WIDETAG;
 372     if (all_threads == 0) {
 373         if(SymbolValue(FREE_TLS_INDEX,0)==UNBOUND_MARKER_WIDETAG) {
 374             SetSymbolValue
 375                 (FREE_TLS_INDEX,
 376                  /* FIXME: should be MAX_INTERRUPTS -1 ? */
 377                  make_fixnum(MAX_INTERRUPTS+
 378                              sizeof(struct thread)/sizeof(lispobj)),
 379                  0);
 380             SetSymbolValue(TLS_INDEX_LOCK,make_fixnum(0),0);
 381         }
 382 #define STATIC_TLS_INIT(sym,field) \
 383   ((struct symbol *)(sym-OTHER_POINTER_LOWTAG))->tls_index= \
 384   make_fixnum(THREAD_SLOT_OFFSET_WORDS(field))
 385
 386         STATIC_TLS_INIT(BINDING_STACK_START,binding_stack_start);
 387         STATIC_TLS_INIT(BINDING_STACK_POINTER,binding_stack_pointer);
 388         STATIC_TLS_INIT(CONTROL_STACK_START,control_stack_start);
 389         STATIC_TLS_INIT(CONTROL_STACK_END,control_stack_end);
 390         STATIC_TLS_INIT(ALIEN_STACK,alien_stack_pointer);
 391 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 392         STATIC_TLS_INIT(PSEUDO_ATOMIC_BITS,pseudo_atomic_bits);
 393 #endif
 394 #undef STATIC_TLS_INIT
 395     }
 396 #endif
 397
 398     th=&per_thread->thread;
 399     th->control_stack_start = spaces;
 400     th->binding_stack_start=
 401         (lispobj*)((void*)th->control_stack_start+THREAD_CONTROL_STACK_SIZE);
 402     th->control_stack_end = th->binding_stack_start;
 403     th->alien_stack_start=
 404         (lispobj*)((void*)th->binding_stack_start+BINDING_STACK_SIZE);
 405     th->binding_stack_pointer=th->binding_stack_start;
 406     th->this=th;
 407     th->os_thread=0;
 408     th->state=STATE_RUNNING;
 409 #ifdef LISP_FEATURE_STACK_GROWS_DOWNWARD_NOT_UPWARD
 410     th->alien_stack_pointer=((void *)th->alien_stack_start
 411                              + ALIEN_STACK_SIZE-N_WORD_BYTES);
 412 #else
 413     th->alien_stack_pointer=((void *)th->alien_stack_start);
 414 #endif
 415 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 416     th->pseudo_atomic_bits=0;
 417 #endif
 418 #ifdef LISP_FEATURE_GENCGC
 419     gc_set_region_empty(&th->alloc_region);
 420 #endif
 421
 422 #ifndef LISP_FEATURE_SB_THREAD
 423     /* the tls-points-into-struct-thread trick is only good for threaded
 424      * sbcl, because unithread sbcl doesn't have tls.  So, we copy the
 425      * appropriate values from struct thread here, and make sure that
 426      * we use the appropriate SymbolValue macros to access any of the
 427      * variable quantities from the C runtime.  It's not quite OAOOM,
 428      * it just feels like it */
 429     SetSymbolValue(BINDING_STACK_START,(lispobj)th->binding_stack_start,th);
 430     SetSymbolValue(CONTROL_STACK_START,(lispobj)th->control_stack_start,th);
 431     SetSymbolValue(CONTROL_STACK_END,(lispobj)th->control_stack_end,th);
 432 #if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
 433     SetSymbolValue(BINDING_STACK_POINTER,(lispobj)th->binding_stack_pointer,th);
 434     SetSymbolValue(ALIEN_STACK,(lispobj)th->alien_stack_pointer,th);
 435     SetSymbolValue(PSEUDO_ATOMIC_BITS,(lispobj)th->pseudo_atomic_bits,th);
 436 #else
 437     current_binding_stack_pointer=th->binding_stack_pointer;
 438     current_control_stack_pointer=th->control_stack_start;
 439 #endif
 440 #endif
 441     bind_variable(CURRENT_CATCH_BLOCK,make_fixnum(0),th);
 442     bind_variable(CURRENT_UNWIND_PROTECT_BLOCK,make_fixnum(0),th);
 443     bind_variable(FREE_INTERRUPT_CONTEXT_INDEX,make_fixnum(0),th);
 444     bind_variable(INTERRUPT_PENDING, NIL,th);
 445     bind_variable(INTERRUPTS_ENABLED,T,th);
 446     bind_variable(GC_PENDING,NIL,th);
 447 #ifdef LISP_FEATURE_SB_THREAD
 448     bind_variable(STOP_FOR_GC_PENDING,NIL,th);
 449 #endif
 450
 451     th->interrupt_data = (struct interrupt_data *)
 452         os_validate(0,(sizeof (struct interrupt_data)));
 453     if (!th->interrupt_data) {
 454         free_thread_struct(th);
 455         return 0;
 456     }
 457     th->interrupt_data->pending_handler = 0;
 458     th->no_tls_value_marker=initial_function;
 459
 460     th->stepping = NIL;
 461     return th;
 462 }
 463
 464 void create_initial_thread(lispobj initial_function) {
 465     struct thread *th=create_thread_struct(initial_function);
 466     if(th) {
 467         initial_thread_trampoline(th); /* no return */
 468     } else lose("can't create initial thread\n");
 469 }
 470
 471 #ifdef LISP_FEATURE_SB_THREAD
 472
 473 #ifndef __USE_XOPEN2K
 474 extern int pthread_attr_setstack (pthread_attr_t *__attr, void *__stackaddr,
 475                                   size_t __stacksize);
 476 #endif
 477
 478 boolean create_os_thread(struct thread *th,os_thread_t *kid_tid)
 479 {
 480     /* The new thread inherits the restrictive signal mask set here,
 481      * and enables signals again when it is set up properly. */
 482     pthread_attr_t attr;
 483     sigset_t newset,oldset;
 484     boolean r=1;
 485     int retcode, initcode, sizecode, addrcode;
 486
 487     FSHOW_SIGNAL((stderr,"/create_os_thread: creating new thread\n"));
 488
 489 #ifdef LOCK_CREATE_THREAD
 490     retcode = pthread_mutex_lock(&create_thread_lock);
 491     gc_assert(retcode == 0);
 492     FSHOW_SIGNAL((stderr,"/create_os_thread: got lock\n"));
 493 #endif
 494     sigemptyset(&newset);
 495     /* Blocking deferrable signals is enough, no need to block
 496      * SIG_STOP_FOR_GC because the child process is not linked onto
 497      * all_threads until it's ready. */
 498     sigaddset_deferrable(&newset);
 499     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 500
 501 #if defined(LISP_FEATURE_DARWIN)
 502 #define CONTROL_STACK_ADJUST 8192 /* darwin wants page-aligned stacks */
 503 #else
 504 #define CONTROL_STACK_ADJUST 16
 505 #endif
 506
 507     if((initcode = pthread_attr_init(&attr)) ||
 508        /* FIXME: why do we even have this in the first place? */
 509        (pthread_attr_setstack(&attr,th->control_stack_start,
 510                               THREAD_CONTROL_STACK_SIZE-CONTROL_STACK_ADJUST)) ||
 511 #undef CONTROL_STACK_ADJUST
 512        (retcode = pthread_create
 513         (kid_tid,&attr,(void *(*)(void *))new_thread_trampoline,th))) {
 514         FSHOW_SIGNAL((stderr, "init, size, addr = %d, %d, %d\n", initcode, sizecode, addrcode));
 515         FSHOW_SIGNAL((stderr, printf("pthread_create returned %d, errno %d\n", retcode, errno)));
 516         FSHOW_SIGNAL((stderr, "wanted stack size %d, min stack size %d\n",
 517                       THREAD_CONTROL_STACK_SIZE-16, PTHREAD_STACK_MIN));
 518         if(retcode < 0) {
 519             perror("create_os_thread");
 520         }
 521         r=0;
 522     }
 523 #ifdef QUEUE_FREEABLE_THREAD_STACKS
 524     free_freeable_stacks();
 525 #endif
 526     thread_sigmask(SIG_SETMASK,&oldset,0);
 527 #ifdef LOCK_CREATE_THREAD
 528     retcode = pthread_mutex_unlock(&create_thread_lock);
 529     gc_assert(retcode == 0);
 530     FSHOW_SIGNAL((stderr,"/create_os_thread: released lock\n"));
 531 #endif
 532     return r;
 533 }
 534
 535 os_thread_t create_thread(lispobj initial_function) {
 536     struct thread *th;
 537     os_thread_t kid_tid;
 538
 539     /* Assuming that a fresh thread struct has no lisp objects in it,
 540      * linking it to all_threads can be left to the thread itself
 541      * without fear of gc lossage. initial_function violates this
 542      * assumption and must stay pinned until the child starts up. */
 543     th = create_thread_struct(initial_function);
 544     if(th==0) return 0;
 545
 546     if (create_os_thread(th,&kid_tid)) {
 547         return kid_tid;
 548     } else {
 549         free_thread_struct(th);
 550         return 0;
 551     }
 552 }
 553
 554 /* Send the signo to os_thread, retry if the rt signal queue is
 555  * full. */
 556 int
 557 kill_thread_safely(os_thread_t os_thread, int signo)
 558 {
 559     int r;
 560     /* The man page does not mention EAGAIN as a valid return value
 561      * for either pthread_kill or kill. But that's theory, this is
 562      * practice. By waiting here we assume that the delivery of this
 563      * signal is not necessary for the delivery of the signals in the
 564      * queue. In other words, we _assume_ there are no deadlocks. */
 565     while ((r=pthread_kill(os_thread,signo))==EAGAIN) {
 566         /* wait a bit then try again in the hope of the rt signal
 567          * queue not being full */
 568         FSHOW_SIGNAL((stderr,"/rt signal queue full\n"));
 569         /* FIXME: some kind of backoff (random, exponential) would be
 570          * nice. */
 571         sleep(1);
 572     }
 573     return r;
 574 }
 575
 576 int signal_interrupt_thread(os_thread_t os_thread)
 577 {
 578     int status = kill_thread_safely(os_thread, SIG_INTERRUPT_THREAD);
 579     if (status == 0) {
 580         return 0;
 581     } else if (status == ESRCH) {
 582         return -1;
 583     } else {
 584         lose("cannot send SIG_INTERRUPT_THREAD to thread=%lu: %d, %s\n",
 585              os_thread, status, strerror(status));
 586     }
 587 }
 588
 589 /* stopping the world is a two-stage process.  From this thread we signal
 590  * all the others with SIG_STOP_FOR_GC.  The handler for this signal does
 591  * the usual pseudo-atomic checks (we don't want to stop a thread while
 592  * it's in the middle of allocation) then waits for another SIG_STOP_FOR_GC.
 593  */
 594
 595 /* To avoid deadlocks when gc stops the world all clients of each
 596  * mutex must enable or disable SIG_STOP_FOR_GC for the duration of
 597  * holding the lock, but they must agree on which. */
 598 void gc_stop_the_world()
 599 {
 600     struct thread *p,*th=arch_os_get_current_thread();
 601     int status, lock_ret;
 602 #ifdef LOCK_CREATE_THREAD
 603     /* KLUDGE: Stopping the thread during pthread_create() causes deadlock
 604      * on FreeBSD. */
 605     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on create_thread_lock, thread=%lu\n",
 606                   th->os_thread));
 607     lock_ret = pthread_mutex_lock(&create_thread_lock);
 608     gc_assert(lock_ret == 0);
 609     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got create_thread_lock, thread=%lu\n",
 610                   th->os_thread));
 611 #endif
 612     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock, thread=%lu\n",
 613                   th->os_thread));
 614     /* keep threads from starting while the world is stopped. */
 615     lock_ret = pthread_mutex_lock(&all_threads_lock);      \
 616     gc_assert(lock_ret == 0);
 617
 618     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock, thread=%lu\n",
 619                   th->os_thread));
 620     /* stop all other threads by sending them SIG_STOP_FOR_GC */
 621     for(p=all_threads; p; p=p->next) {
 622         gc_assert(p->os_thread != 0);
 623         FSHOW_SIGNAL((stderr,"/gc_stop_the_world: p->state: %x\n", p->state));
 624         if((p!=th) && ((p->state==STATE_RUNNING))) {
 625             FSHOW_SIGNAL((stderr,"/gc_stop_the_world: suspending %x, os_thread %x\n",
 626                           p, p->os_thread));
 627             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 628             if (status==ESRCH) {
 629                 /* This thread has exited. */
 630                 gc_assert(p->state==STATE_DEAD);
 631             } else if (status) {
 632                 lose("cannot send suspend thread=%lu: %d, %s\n",
 633                      p->os_thread,status,strerror(status));
 634             }
 635         }
 636     }
 637     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:signals sent\n"));
 638     /* wait for the running threads to stop or finish */
 639     for(p=all_threads;p;) {
 640         FSHOW_SIGNAL((stderr,"/gc_stop_the_world: th: %p, p: %p\n", th, p));
 641         if((p!=th) && (p->state==STATE_RUNNING)) {
 642             sched_yield();
 643         } else {
 644             p=p->next;
 645         }
 646     }
 647     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:end\n"));
 648 }
 649
 650 void gc_start_the_world()
 651 {
 652     struct thread *p,*th=arch_os_get_current_thread();
 653     int status, lock_ret;
 654     /* if a resumed thread creates a new thread before we're done with
 655      * this loop, the new thread will get consed on the front of
 656      * all_threads, but it won't have been stopped so won't need
 657      * restarting */
 658     FSHOW_SIGNAL((stderr,"/gc_start_the_world:begin\n"));
 659     for(p=all_threads;p;p=p->next) {
 660         gc_assert(p->os_thread!=0);
 661         if((p!=th) && (p->state!=STATE_DEAD)) {
 662             if(p->state!=STATE_SUSPENDED) {
 663                 lose("gc_start_the_world: wrong thread state is %d\n",
 664                      fixnum_value(p->state));
 665             }
 666             FSHOW_SIGNAL((stderr, "/gc_start_the_world: resuming %lu\n",
 667                           p->os_thread));
 668             p->state=STATE_RUNNING;
 669
 670 #if defined(SIG_RESUME_FROM_GC)
 671             status=kill_thread_safely(p->os_thread,SIG_RESUME_FROM_GC);
 672 #else
 673             status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
 674 #endif
 675             if (status) {
 676                 lose("cannot resume thread=%lu: %d, %s\n",
 677                      p->os_thread,status,strerror(status));
 678             }
 679         }
 680     }
 681     /* If we waited here until all threads leave STATE_SUSPENDED, then
 682      * SIG_STOP_FOR_GC wouldn't need to be a rt signal. That has some
 683      * performance implications, but does away with the 'rt signal
 684      * queue full' problem. */
 685
 686     lock_ret = pthread_mutex_unlock(&all_threads_lock);
 687     gc_assert(lock_ret == 0);
 688 #ifdef LOCK_CREATE_THREAD
 689     lock_ret = pthread_mutex_unlock(&create_thread_lock);
 690     gc_assert(lock_ret == 0);
 691 #endif
 692
 693     FSHOW_SIGNAL((stderr,"/gc_start_the_world:end\n"));
 694 }
 695 #endif