malloc/arena.c

   1 /* Malloc implementation for multiple threads without lock contention.
   2    Copyright (C) 2001 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Wolfram Gloger <wg@malloc.de>, 2001.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public License as
   8    published by the Free Software Foundation; either version 2.1 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 /* $Id$ */
  22
  23 /* Compile-time constants.  */
  24
  25 #define HEAP_MIN_SIZE (32*1024)
  26 #ifndef HEAP_MAX_SIZE
  27 #define HEAP_MAX_SIZE (1024*1024) /* must be a power of two */
  28 #endif
  29
  30 /* HEAP_MIN_SIZE and HEAP_MAX_SIZE limit the size of mmap()ed heaps
  31    that are dynamically created for multi-threaded programs.  The
  32    maximum size must be a power of two, for fast determination of
  33    which heap belongs to a chunk.  It should be much larger than the
  34    mmap threshold, so that requests with a size just below that
  35    threshold can be fulfilled without creating too many heaps.  */
  36
  37
  38 #ifndef THREAD_STATS
  39 #define THREAD_STATS 0
  40 #endif
  41
  42 /* If THREAD_STATS is non-zero, some statistics on mutex locking are
  43    computed.  */
  44
  45 /***************************************************************************/
  46
  47 #define top(ar_ptr) ((ar_ptr)->top)
  48
  49 /* A heap is a single contiguous memory region holding (coalesceable)
  50    malloc_chunks.  It is allocated with mmap() and always starts at an
  51    address aligned to HEAP_MAX_SIZE.  Not used unless compiling with
  52    USE_ARENAS. */
  53
  54 typedef struct _heap_info {
  55   mstate ar_ptr; /* Arena for this heap. */
  56   struct _heap_info *prev; /* Previous heap. */
  57   size_t size;   /* Current size in bytes. */
  58   size_t pad;    /* Make sure the following data is properly aligned. */
  59 } heap_info;
  60
  61 /* Thread specific data */
  62
  63 static tsd_key_t arena_key;
  64 static mutex_t list_lock;
  65
  66 #if THREAD_STATS
  67 static int stat_n_heaps;
  68 #define THREAD_STAT(x) x
  69 #else
  70 #define THREAD_STAT(x) do ; while(0)
  71 #endif
  72
  73 /* Mapped memory in non-main arenas (reliable only for NO_THREADS). */
  74 static unsigned long arena_mem;
  75
  76 /**************************************************************************/
  77
  78 #if USE_ARENAS
  79
  80 /* arena_get() acquires an arena and locks the corresponding mutex.
  81    First, try the one last locked successfully by this thread.  (This
  82    is the common case and handled with a macro for speed.)  Then, loop
  83    once over the circularly linked list of arenas.  If no arena is
  84    readily available, create a new one.  In this latter case, `size'
  85    is just a hint as to how much memory will be required immediately
  86    in the new arena. */
  87
  88 #define arena_get(ptr, size) do { \
  89   Void_t *vptr = NULL; \
  90   ptr = (mstate)tsd_getspecific(arena_key, vptr); \
  91   if(ptr && !mutex_trylock(&ptr->mutex)) { \
  92     THREAD_STAT(++(ptr->stat_lock_direct)); \
  93   } else \
  94     ptr = arena_get2(ptr, (size)); \
  95 } while(0)
  96
  97 /* find the heap and corresponding arena for a given ptr */
  98
  99 #define heap_for_ptr(ptr) \
 100  ((heap_info *)((unsigned long)(ptr) & ~(HEAP_MAX_SIZE-1)))
 101 #define arena_for_chunk(ptr) \
 102  (chunk_non_main_arena(ptr) ? heap_for_ptr(ptr)->ar_ptr : &main_arena)
 103
 104 #else /* !USE_ARENAS */
 105
 106 /* There is only one arena, main_arena. */
 107
 108 #if THREAD_STATS
 109 #define arena_get(ar_ptr, sz) do { \
 110   ar_ptr = &main_arena; \
 111   if(!mutex_trylock(&ar_ptr->mutex)) \
 112     ++(ar_ptr->stat_lock_direct); \
 113   else { \
 114     (void)mutex_lock(&ar_ptr->mutex); \
 115     ++(ar_ptr->stat_lock_wait); \
 116   } \
 117 } while(0)
 118 #else
 119 #define arena_get(ar_ptr, sz) do { \
 120   ar_ptr = &main_arena; \
 121   (void)mutex_lock(&ar_ptr->mutex); \
 122 } while(0)
 123 #endif
 124 #define arena_for_chunk(ptr) (&main_arena)
 125
 126 #endif /* USE_ARENAS */
 127
 128 /**************************************************************************/
 129
 130 #ifndef NO_THREADS
 131
 132 /* atfork support.  */
 133
 134 static __malloc_ptr_t (*save_malloc_hook) __MALLOC_P ((size_t __size,
 135                                                        __const __malloc_ptr_t));
 136 static void           (*save_free_hook) __MALLOC_P ((__malloc_ptr_t __ptr,
 137                                                      __const __malloc_ptr_t));
 138 static Void_t*        save_arena;
 139
 140 /* Magic value for the thread-specific arena pointer when
 141    malloc_atfork() is in use.  */
 142
 143 #define ATFORK_ARENA_PTR ((Void_t*)-1)
 144
 145 /* The following hooks are used while the `atfork' handling mechanism
 146    is active. */
 147
 148 static Void_t*
 149 malloc_atfork(size_t sz, const Void_t *caller)
 150 {
 151   Void_t *vptr = NULL;
 152   Void_t *victim;
 153
 154   tsd_getspecific(arena_key, vptr);
 155   if(vptr == ATFORK_ARENA_PTR) {
 156     /* We are the only thread that may allocate at all.  */
 157     if(save_malloc_hook != malloc_check) {
 158       return _int_malloc(&main_arena, sz);
 159     } else {
 160       if(top_check()<0)
 161         return 0;
 162       victim = _int_malloc(&main_arena, sz+1);
 163       return mem2mem_check(victim, sz);
 164     }
 165   } else {
 166     /* Suspend the thread until the `atfork' handlers have completed.
 167        By that time, the hooks will have been reset as well, so that
 168        mALLOc() can be used again. */
 169     (void)mutex_lock(&list_lock);
 170     (void)mutex_unlock(&list_lock);
 171     return public_mALLOc(sz);
 172   }
 173 }
 174
 175 static void
 176 free_atfork(Void_t* mem, const Void_t *caller)
 177 {
 178   Void_t *vptr = NULL;
 179   mstate ar_ptr;
 180   mchunkptr p;                          /* chunk corresponding to mem */
 181
 182   if (mem == 0)                              /* free(0) has no effect */
 183     return;
 184
 185   p = mem2chunk(mem);         /* do not bother to replicate free_check here */
 186
 187 #if HAVE_MMAP
 188   if (chunk_is_mmapped(p))                       /* release mmapped memory. */
 189   {
 190     munmap_chunk(p);
 191     return;
 192   }
 193 #endif
 194
 195   ar_ptr = arena_for_chunk(p);
 196   tsd_getspecific(arena_key, vptr);
 197   if(vptr != ATFORK_ARENA_PTR)
 198     (void)mutex_lock(&ar_ptr->mutex);
 199   _int_free(ar_ptr, mem);
 200   if(vptr != ATFORK_ARENA_PTR)
 201     (void)mutex_unlock(&ar_ptr->mutex);
 202 }
 203
 204 /* The following two functions are registered via thread_atfork() to
 205    make sure that the mutexes remain in a consistent state in the
 206    fork()ed version of a thread.  Also adapt the malloc and free hooks
 207    temporarily, because the `atfork' handler mechanism may use
 208    malloc/free internally (e.g. in LinuxThreads). */
 209
 210 static void
 211 ptmalloc_lock_all __MALLOC_P((void))
 212 {
 213   mstate ar_ptr;
 214
 215   (void)mutex_lock(&list_lock);
 216   for(ar_ptr = &main_arena;;) {
 217     (void)mutex_lock(&ar_ptr->mutex);
 218     ar_ptr = ar_ptr->next;
 219     if(ar_ptr == &main_arena) break;
 220   }
 221   save_malloc_hook = __malloc_hook;
 222   save_free_hook = __free_hook;
 223   __malloc_hook = malloc_atfork;
 224   __free_hook = free_atfork;
 225   /* Only the current thread may perform malloc/free calls now. */
 226   tsd_getspecific(arena_key, save_arena);
 227   tsd_setspecific(arena_key, ATFORK_ARENA_PTR);
 228 }
 229
 230 static void
 231 ptmalloc_unlock_all __MALLOC_P((void))
 232 {
 233   mstate ar_ptr;
 234
 235   tsd_setspecific(arena_key, save_arena);
 236   __malloc_hook = save_malloc_hook;
 237   __free_hook = save_free_hook;
 238   for(ar_ptr = &main_arena;;) {
 239     (void)mutex_unlock(&ar_ptr->mutex);
 240     ar_ptr = ar_ptr->next;
 241     if(ar_ptr == &main_arena) break;
 242   }
 243   (void)mutex_unlock(&list_lock);
 244 }
 245
 246 #ifdef __linux__
 247
 248 /* In LinuxThreads, unlocking a mutex in the child process after a
 249    fork() is currently unsafe, whereas re-initializing it is safe and
 250    does not leak resources.  Therefore, a special atfork handler is
 251    installed for the child. */
 252
 253 static void
 254 ptmalloc_unlock_all2 __MALLOC_P((void))
 255 {
 256   mstate ar_ptr;
 257
 258 #if defined _LIBC || defined MALLOC_HOOKS
 259   tsd_setspecific(arena_key, save_arena);
 260   __malloc_hook = save_malloc_hook;
 261   __free_hook = save_free_hook;
 262 #endif
 263   for(ar_ptr = &main_arena;;) {
 264     (void)mutex_init(&ar_ptr->mutex);
 265     ar_ptr = ar_ptr->next;
 266     if(ar_ptr == &main_arena) break;
 267   }
 268   (void)mutex_init(&list_lock);
 269 }
 270
 271 #else
 272
 273 #define ptmalloc_unlock_all2 ptmalloc_unlock_all
 274
 275 #endif
 276
 277 #endif /* !defined NO_THREADS */
 278
 279 /* Already initialized? */
 280 int __malloc_initialized = -1;
 281
 282 /* Initialization routine. */
 283 #ifdef _LIBC
 284 #include <string.h>
 285 extern char **_environ;
 286
 287 static char *
 288 internal_function
 289 next_env_entry (char ***position)
 290 {
 291   char **current = *position;
 292   char *result = NULL;
 293
 294   while (*current != NULL)
 295     {
 296       if (__builtin_expect ((*current)[0] == 'M', 0)
 297           && (*current)[1] == 'A'
 298           && (*current)[2] == 'L'
 299           && (*current)[3] == 'L'
 300           && (*current)[4] == 'O'
 301           && (*current)[5] == 'C'
 302           && (*current)[6] == '_')
 303         {
 304           result = &(*current)[7];
 305
 306           /* Save current position for next visit.  */
 307           *position = ++current;
 308
 309           break;
 310         }
 311
 312       ++current;
 313     }
 314
 315   return result;
 316 }
 317 #endif /* _LIBC */
 318
 319 static void
 320 ptmalloc_init __MALLOC_P((void))
 321 {
 322 #if __STD_C
 323   const char* s;
 324 #else
 325   char* s;
 326 #endif
 327   int secure = 0;
 328
 329   if(__malloc_initialized >= 0) return;
 330   __malloc_initialized = 0;
 331
 332   mp_.top_pad        = DEFAULT_TOP_PAD;
 333   mp_.n_mmaps_max    = DEFAULT_MMAP_MAX;
 334   mp_.mmap_threshold = DEFAULT_MMAP_THRESHOLD;
 335   mp_.trim_threshold = DEFAULT_TRIM_THRESHOLD;
 336   mp_.pagesize       = malloc_getpagesize;
 337
 338 #ifndef NO_THREADS
 339   /* With some threads implementations, creating thread-specific data
 340      or initializing a mutex may call malloc() itself.  Provide a
 341      simple starter version (realloc() won't work). */
 342   save_malloc_hook = __malloc_hook;
 343   save_free_hook = __free_hook;
 344   __malloc_hook = malloc_starter;
 345   __free_hook = free_starter;
 346 #ifdef _LIBC
 347   /* Initialize the pthreads interface. */
 348   if (__pthread_initialize != NULL)
 349     __pthread_initialize();
 350 #endif
 351 #endif /* !defined NO_THREADS */
 352   mutex_init(&main_arena.mutex);
 353   main_arena.next = &main_arena;
 354
 355   mutex_init(&list_lock);
 356   tsd_key_create(&arena_key, NULL);
 357   tsd_setspecific(arena_key, (Void_t *)&main_arena);
 358   thread_atfork(ptmalloc_lock_all, ptmalloc_unlock_all, ptmalloc_unlock_all2);
 359 #ifndef NO_THREADS
 360   __malloc_hook = save_malloc_hook;
 361   __free_hook = save_free_hook;
 362 #endif
 363 #ifdef _LIBC
 364   secure = __libc_enable_secure;
 365   s = NULL;
 366   {
 367     char **runp = _environ;
 368     char *envline;
 369
 370     while (__builtin_expect ((envline = next_env_entry (&runp)) != NULL,
 371                              0))
 372       {
 373         size_t len = strcspn (envline, "=");
 374
 375         if (envline[len] != '=')
 376           /* This is a "MALLOC_" variable at the end of the string
 377              without a '=' character.  Ignore it since otherwise we
 378              will access invalid memory below.  */
 379           continue;
 380
 381         switch (len)
 382           {
 383           case 6:
 384             if (memcmp (envline, "CHECK_", 6) == 0)
 385               s = &envline[7];
 386             break;
 387           case 8:
 388             if (! secure && memcmp (envline, "TOP_PAD_", 8) == 0)
 389               mALLOPt(M_TOP_PAD, atoi(&envline[9]));
 390             break;
 391           case 9:
 392             if (! secure && memcmp (envline, "MMAP_MAX_", 9) == 0)
 393               mALLOPt(M_MMAP_MAX, atoi(&envline[10]));
 394             break;
 395           case 15:
 396             if (! secure)
 397               {
 398                 if (memcmp (envline, "TRIM_THRESHOLD_", 15) == 0)
 399                   mALLOPt(M_TRIM_THRESHOLD, atoi(&envline[16]));
 400                 else if (memcmp (envline, "MMAP_THRESHOLD_", 15) == 0)
 401                   mALLOPt(M_MMAP_THRESHOLD, atoi(&envline[16]));
 402               }
 403             break;
 404           default:
 405             break;
 406           }
 407       }
 408   }
 409 #else
 410   if (! secure)
 411     {
 412       if((s = getenv("MALLOC_TRIM_THRESHOLD_")))
 413         mALLOPt(M_TRIM_THRESHOLD, atoi(s));
 414       if((s = getenv("MALLOC_TOP_PAD_")))
 415         mALLOPt(M_TOP_PAD, atoi(s));
 416       if((s = getenv("MALLOC_MMAP_THRESHOLD_")))
 417         mALLOPt(M_MMAP_THRESHOLD, atoi(s));
 418       if((s = getenv("MALLOC_MMAP_MAX_")))
 419         mALLOPt(M_MMAP_MAX, atoi(s));
 420     }
 421   s = getenv("MALLOC_CHECK_");
 422 #endif
 423   if(s) {
 424     if(s[0]) mALLOPt(M_CHECK_ACTION, (int)(s[0] - '0'));
 425     __malloc_check_init();
 426   }
 427   if(__malloc_initialize_hook != NULL)
 428     (*__malloc_initialize_hook)();
 429   __malloc_initialized = 1;
 430 }
 431
 432 /* There are platforms (e.g. Hurd) with a link-time hook mechanism. */
 433 #ifdef thread_atfork_static
 434 thread_atfork_static(ptmalloc_lock_all, ptmalloc_unlock_all, \
 435                      ptmalloc_unlock_all2)
 436 #endif
 437
 438 \f
 439
 440 /* Managing heaps and arenas (for concurrent threads) */
 441
 442 #if USE_ARENAS
 443
 444 #if MALLOC_DEBUG > 1
 445
 446 /* Print the complete contents of a single heap to stderr. */
 447
 448 static void
 449 #if __STD_C
 450 dump_heap(heap_info *heap)
 451 #else
 452 dump_heap(heap) heap_info *heap;
 453 #endif
 454 {
 455   char *ptr;
 456   mchunkptr p;
 457
 458   fprintf(stderr, "Heap %p, size %10lx:\n", heap, (long)heap->size);
 459   ptr = (heap->ar_ptr != (mstate)(heap+1)) ?
 460     (char*)(heap + 1) : (char*)(heap + 1) + sizeof(struct malloc_state);
 461   p = (mchunkptr)(((unsigned long)ptr + MALLOC_ALIGN_MASK) &
 462                   ~MALLOC_ALIGN_MASK);
 463   for(;;) {
 464     fprintf(stderr, "chunk %p size %10lx", p, (long)p->size);
 465     if(p == top(heap->ar_ptr)) {
 466       fprintf(stderr, " (top)\n");
 467       break;
 468     } else if(p->size == (0|PREV_INUSE)) {
 469       fprintf(stderr, " (fence)\n");
 470       break;
 471     }
 472     fprintf(stderr, "\n");
 473     p = next_chunk(p);
 474   }
 475 }
 476
 477 #endif /* MALLOC_DEBUG > 1 */
 478
 479 /* Create a new heap.  size is automatically rounded up to a multiple
 480    of the page size. */
 481
 482 static heap_info *
 483 internal_function
 484 #if __STD_C
 485 new_heap(size_t size, size_t top_pad)
 486 #else
 487 new_heap(size, top_pad) size_t size, top_pad;
 488 #endif
 489 {
 490   size_t page_mask = malloc_getpagesize - 1;
 491   char *p1, *p2;
 492   unsigned long ul;
 493   heap_info *h;
 494
 495   if(size+top_pad < HEAP_MIN_SIZE)
 496     size = HEAP_MIN_SIZE;
 497   else if(size+top_pad <= HEAP_MAX_SIZE)
 498     size += top_pad;
 499   else if(size > HEAP_MAX_SIZE)
 500     return 0;
 501   else
 502     size = HEAP_MAX_SIZE;
 503   size = (size + page_mask) & ~page_mask;
 504
 505   /* A memory region aligned to a multiple of HEAP_MAX_SIZE is needed.
 506      No swap space needs to be reserved for the following large
 507      mapping (on Linux, this is the case for all non-writable mappings
 508      anyway). */
 509   p1 = (char *)MMAP(0, HEAP_MAX_SIZE<<1, PROT_NONE, MAP_PRIVATE|MAP_NORESERVE);
 510   if(p1 != MAP_FAILED) {
 511     p2 = (char *)(((unsigned long)p1 + (HEAP_MAX_SIZE-1)) & ~(HEAP_MAX_SIZE-1));
 512     ul = p2 - p1;
 513     munmap(p1, ul);
 514     munmap(p2 + HEAP_MAX_SIZE, HEAP_MAX_SIZE - ul);
 515   } else {
 516     /* Try to take the chance that an allocation of only HEAP_MAX_SIZE
 517        is already aligned. */
 518     p2 = (char *)MMAP(0, HEAP_MAX_SIZE, PROT_NONE, MAP_PRIVATE|MAP_NORESERVE);
 519     if(p2 == MAP_FAILED)
 520       return 0;
 521     if((unsigned long)p2 & (HEAP_MAX_SIZE-1)) {
 522       munmap(p2, HEAP_MAX_SIZE);
 523       return 0;
 524     }
 525   }
 526   if(mprotect(p2, size, PROT_READ|PROT_WRITE) != 0) {
 527     munmap(p2, HEAP_MAX_SIZE);
 528     return 0;
 529   }
 530   h = (heap_info *)p2;
 531   h->size = size;
 532   THREAD_STAT(stat_n_heaps++);
 533   return h;
 534 }
 535
 536 /* Grow or shrink a heap.  size is automatically rounded up to a
 537    multiple of the page size if it is positive. */
 538
 539 static int
 540 #if __STD_C
 541 grow_heap(heap_info *h, long diff)
 542 #else
 543 grow_heap(h, diff) heap_info *h; long diff;
 544 #endif
 545 {
 546   size_t page_mask = malloc_getpagesize - 1;
 547   long new_size;
 548
 549   if(diff >= 0) {
 550     diff = (diff + page_mask) & ~page_mask;
 551     new_size = (long)h->size + diff;
 552     if(new_size > HEAP_MAX_SIZE)
 553       return -1;
 554     if(mprotect((char *)h + h->size, diff, PROT_READ|PROT_WRITE) != 0)
 555       return -2;
 556   } else {
 557     new_size = (long)h->size + diff;
 558     if(new_size < (long)sizeof(*h))
 559       return -1;
 560     /* Try to re-map the extra heap space freshly to save memory, and
 561        make it inaccessible. */
 562     if((char *)MMAP((char *)h + new_size, -diff, PROT_NONE,
 563                     MAP_PRIVATE|MAP_FIXED) == (char *) MAP_FAILED)
 564       return -2;
 565     /*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/
 566   }
 567   h->size = new_size;
 568   return 0;
 569 }
 570
 571 /* Delete a heap. */
 572
 573 #define delete_heap(heap) munmap((char*)(heap), HEAP_MAX_SIZE)
 574
 575 static int
 576 internal_function
 577 #if __STD_C
 578 heap_trim(heap_info *heap, size_t pad)
 579 #else
 580 heap_trim(heap, pad) heap_info *heap; size_t pad;
 581 #endif
 582 {
 583   mstate ar_ptr = heap->ar_ptr;
 584   unsigned long pagesz = mp_.pagesize;
 585   mchunkptr top_chunk = top(ar_ptr), p, bck, fwd;
 586   heap_info *prev_heap;
 587   long new_size, top_size, extra;
 588
 589   /* Can this heap go away completely? */
 590   while(top_chunk == chunk_at_offset(heap, sizeof(*heap))) {
 591     prev_heap = heap->prev;
 592     p = chunk_at_offset(prev_heap, prev_heap->size - (MINSIZE-2*SIZE_SZ));
 593     assert(p->size == (0|PREV_INUSE)); /* must be fencepost */
 594     p = prev_chunk(p);
 595     new_size = chunksize(p) + (MINSIZE-2*SIZE_SZ);
 596     assert(new_size>0 && new_size<(long)(2*MINSIZE));
 597     if(!prev_inuse(p))
 598       new_size += p->prev_size;
 599     assert(new_size>0 && new_size<HEAP_MAX_SIZE);
 600     if(new_size + (HEAP_MAX_SIZE - prev_heap->size) < pad + MINSIZE + pagesz)
 601       break;
 602     ar_ptr->system_mem -= heap->size;
 603     arena_mem -= heap->size;
 604     delete_heap(heap);
 605     heap = prev_heap;
 606     if(!prev_inuse(p)) { /* consolidate backward */
 607       p = prev_chunk(p);
 608       unlink(p, bck, fwd);
 609     }
 610     assert(((unsigned long)((char*)p + new_size) & (pagesz-1)) == 0);
 611     assert( ((char*)p + new_size) == ((char*)heap + heap->size) );
 612     top(ar_ptr) = top_chunk = p;
 613     set_head(top_chunk, new_size | PREV_INUSE);
 614     /*check_chunk(ar_ptr, top_chunk);*/
 615   }
 616   top_size = chunksize(top_chunk);
 617   extra = ((top_size - pad - MINSIZE + (pagesz-1))/pagesz - 1) * pagesz;
 618   if(extra < (long)pagesz)
 619     return 0;
 620   /* Try to shrink. */
 621   if(grow_heap(heap, -extra) != 0)
 622     return 0;
 623   ar_ptr->system_mem -= extra;
 624   arena_mem -= extra;
 625
 626   /* Success. Adjust top accordingly. */
 627   set_head(top_chunk, (top_size - extra) | PREV_INUSE);
 628   /*check_chunk(ar_ptr, top_chunk);*/
 629   return 1;
 630 }
 631
 632 static mstate
 633 internal_function
 634 #if __STD_C
 635 arena_get2(mstate a_tsd, size_t size)
 636 #else
 637 arena_get2(a_tsd, size) mstate a_tsd; size_t size;
 638 #endif
 639 {
 640   mstate a;
 641   int err;
 642
 643   if(!a_tsd)
 644     a = a_tsd = &main_arena;
 645   else {
 646     a = a_tsd->next;
 647     if(!a) {
 648       /* This can only happen while initializing the new arena. */
 649       (void)mutex_lock(&main_arena.mutex);
 650       THREAD_STAT(++(main_arena.stat_lock_wait));
 651       return &main_arena;
 652     }
 653   }
 654
 655   /* Check the global, circularly linked list for available arenas. */
 656  repeat:
 657   do {
 658     if(!mutex_trylock(&a->mutex)) {
 659       THREAD_STAT(++(a->stat_lock_loop));
 660       tsd_setspecific(arena_key, (Void_t *)a);
 661       return a;
 662     }
 663     a = a->next;
 664   } while(a != a_tsd);
 665
 666   /* If not even the list_lock can be obtained, try again.  This can
 667      happen during `atfork', or for example on systems where thread
 668      creation makes it temporarily impossible to obtain _any_
 669      locks. */
 670   if(mutex_trylock(&list_lock)) {
 671     a = a_tsd;
 672     goto repeat;
 673   }
 674   (void)mutex_unlock(&list_lock);
 675
 676   /* Nothing immediately available, so generate a new arena.  */
 677   a = _int_new_arena(size);
 678   if(!a)
 679     return 0;
 680
 681   tsd_setspecific(arena_key, (Void_t *)a);
 682   mutex_init(&a->mutex);
 683   err = mutex_lock(&a->mutex); /* remember result */
 684
 685   /* Add the new arena to the global list.  */
 686   (void)mutex_lock(&list_lock);
 687   a->next = main_arena.next;
 688   main_arena.next = a;
 689   (void)mutex_unlock(&list_lock);
 690
 691   if(err) /* locking failed; keep arena for further attempts later */
 692     return 0;
 693
 694   THREAD_STAT(++(a->stat_lock_loop));
 695   return a;
 696 }
 697
 698 /* Create a new arena with initial size "size".  */
 699
 700 mstate
 701 _int_new_arena(size_t size)
 702 {
 703   mstate a;
 704   heap_info *h;
 705   char *ptr;
 706   unsigned long misalign;
 707
 708   h = new_heap(size + (sizeof(*h) + sizeof(*a) + MALLOC_ALIGNMENT),
 709                mp_.top_pad);
 710   if(!h) {
 711     /* Maybe size is too large to fit in a single heap.  So, just try
 712        to create a minimally-sized arena and let _int_malloc() attempt
 713        to deal with the large request via mmap_chunk().  */
 714     h = new_heap(sizeof(*h) + sizeof(*a) + MALLOC_ALIGNMENT, mp_.top_pad);
 715     if(!h)
 716       return 0;
 717   }
 718   a = h->ar_ptr = (mstate)(h+1);
 719   malloc_init_state(a);
 720   /*a->next = NULL;*/
 721   a->system_mem = a->max_system_mem = h->size;
 722   arena_mem += h->size;
 723 #ifdef NO_THREADS
 724   if((unsigned long)(mp_.mmapped_mem + arena_mem + main_arena.system_mem) >
 725      mp_.max_total_mem)
 726     mp_.max_total_mem = mp_.mmapped_mem + arena_mem + main_arena.system_mem;
 727 #endif
 728
 729   /* Set up the top chunk, with proper alignment. */
 730   ptr = (char *)(a + 1);
 731   misalign = (unsigned long)chunk2mem(ptr) & MALLOC_ALIGN_MASK;
 732   if (misalign > 0)
 733     ptr += MALLOC_ALIGNMENT - misalign;
 734   top(a) = (mchunkptr)ptr;
 735   set_head(top(a), (((char*)h + h->size) - ptr) | PREV_INUSE);
 736
 737   return a;
 738 }
 739
 740 #endif /* USE_ARENAS */
 741
 742 /*
 743  * Local variables:
 744  * c-basic-offset: 2
 745  * End:
 746  */