Update.

2002-01-18  Wolfram Gloger  <wg@malloc.de>

	* malloc/malloc.c: Rewrite, adapted from Doug Lea's malloc-2.7.0.c.
	* malloc/malloc.h: Likewise.
	* malloc/arena.c: New file.
	* malloc/hooks.c: New file.
	* malloc/tst-mallocstate.c: New file.
	* malloc/Makefile: Add new testcase tst-mallocstate.
	Add arena.c and hooks.c to distribute.  Fix commented CPPFLAGS.

2002-01-28  Ulrich Drepper  <drepper@redhat.com>

	* stdlib/msort.c: Remove last patch.  The optimization violates the
	same rule which qsort.c had problems with.

2002-01-27  Paul Eggert  <eggert@twinsun.com>

	* stdlib/qsort.c (_quicksort): Do not apply the comparison function
	to a pivot element that lies outside the array to be sorted, as
	ISO C99 requires that the comparison function be called only with
	addresses of array elements [PR libc/2880].

1 files changed, 746 insertions, 0 deletions

diff --git a/malloc/arena.c b/malloc/arena.c
new file mode 100644
index 0000000..8324b68
--- /dev/null
+++ b/malloc/arena.c
@@ -0,0 +1,746 @@
+/* Malloc implementation for multiple threads without lock contention.
+   Copyright (C) 2001 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Wolfram Gloger <wg@malloc.de>, 2001.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If not,
+   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+   Boston, MA 02111-1307, USA.  */
+
+/* $Id$ */
+
+/* Compile-time constants.  */
+
+#define HEAP_MIN_SIZE (32*1024)
+#ifndef HEAP_MAX_SIZE
+#define HEAP_MAX_SIZE (1024*1024) /* must be a power of two */
+#endif
+
+/* HEAP_MIN_SIZE and HEAP_MAX_SIZE limit the size of mmap()ed heaps
+   that are dynamically created for multi-threaded programs.  The
+   maximum size must be a power of two, for fast determination of
+   which heap belongs to a chunk.  It should be much larger than the
+   mmap threshold, so that requests with a size just below that
+   threshold can be fulfilled without creating too many heaps.  */
+
+
+#ifndef THREAD_STATS
+#define THREAD_STATS 0
+#endif
+
+/* If THREAD_STATS is non-zero, some statistics on mutex locking are
+   computed.  */
+
+/***************************************************************************/
+
+#define top(ar_ptr) ((ar_ptr)->top)
+
+/* A heap is a single contiguous memory region holding (coalesceable)
+   malloc_chunks.  It is allocated with mmap() and always starts at an
+   address aligned to HEAP_MAX_SIZE.  Not used unless compiling with
+   USE_ARENAS. */
+
+typedef struct _heap_info {
+  mstate ar_ptr; /* Arena for this heap. */
+  struct _heap_info *prev; /* Previous heap. */
+  size_t size;   /* Current size in bytes. */
+  size_t pad;    /* Make sure the following data is properly aligned. */
+} heap_info;
+
+/* Thread specific data */
+
+static tsd_key_t arena_key;
+static mutex_t list_lock;
+
+#if THREAD_STATS
+static int stat_n_heaps;
+#define THREAD_STAT(x) x
+#else
+#define THREAD_STAT(x) do ; while(0)
+#endif
+
+/* Mapped memory in non-main arenas (reliable only for NO_THREADS). */
+static unsigned long arena_mem;
+
+/**************************************************************************/
+
+#if USE_ARENAS
+
+/* arena_get() acquires an arena and locks the corresponding mutex.
+   First, try the one last locked successfully by this thread.  (This
+   is the common case and handled with a macro for speed.)  Then, loop
+   once over the circularly linked list of arenas.  If no arena is
+   readily available, create a new one.  In this latter case, `size'
+   is just a hint as to how much memory will be required immediately
+   in the new arena. */
+
+#define arena_get(ptr, size) do { \
+  Void_t *vptr = NULL; \
+  ptr = (mstate)tsd_getspecific(arena_key, vptr); \
+  if(ptr && !mutex_trylock(&ptr->mutex)) { \
+    THREAD_STAT(++(ptr->stat_lock_direct)); \
+  } else \
+    ptr = arena_get2(ptr, (size)); \
+} while(0)
+
+/* find the heap and corresponding arena for a given ptr */
+
+#define heap_for_ptr(ptr) \
+ ((heap_info *)((unsigned long)(ptr) & ~(HEAP_MAX_SIZE-1)))
+#define arena_for_chunk(ptr) \
+ (chunk_non_main_arena(ptr) ? heap_for_ptr(ptr)->ar_ptr : &main_arena)
+
+#else /* !USE_ARENAS */
+
+/* There is only one arena, main_arena. */
+
+#if THREAD_STATS
+#define arena_get(ar_ptr, sz) do { \
+  ar_ptr = &main_arena; \
+  if(!mutex_trylock(&ar_ptr->mutex)) \
+    ++(ar_ptr->stat_lock_direct); \
+  else { \
+    (void)mutex_lock(&ar_ptr->mutex); \
+    ++(ar_ptr->stat_lock_wait); \
+  } \
+} while(0)
+#else
+#define arena_get(ar_ptr, sz) do { \
+  ar_ptr = &main_arena; \
+  (void)mutex_lock(&ar_ptr->mutex); \
+} while(0)
+#endif
+#define arena_for_chunk(ptr) (&main_arena)
+
+#endif /* USE_ARENAS */
+
+/**************************************************************************/
+
+#ifndef NO_THREADS
+
+/* atfork support.  */
+
+static __malloc_ptr_t (*save_malloc_hook) __MALLOC_P ((size_t __size,
+						       __const __malloc_ptr_t));
+static void           (*save_free_hook) __MALLOC_P ((__malloc_ptr_t __ptr,
+						     __const __malloc_ptr_t));
+static Void_t*        save_arena;
+
+/* Magic value for the thread-specific arena pointer when
+   malloc_atfork() is in use.  */
+
+#define ATFORK_ARENA_PTR ((Void_t*)-1)
+
+/* The following hooks are used while the `atfork' handling mechanism
+   is active. */
+
+static Void_t*
+malloc_atfork(size_t sz, const Void_t *caller)
+{
+  Void_t *vptr = NULL;
+  Void_t *victim;
+
+  tsd_getspecific(arena_key, vptr);
+  if(vptr == ATFORK_ARENA_PTR) {
+    /* We are the only thread that may allocate at all.  */
+    if(save_malloc_hook != malloc_check) {
+      return _int_malloc(&main_arena, sz);
+    } else {
+      if(top_check()<0)
+        return 0;
+      victim = _int_malloc(&main_arena, sz+1);
+      return mem2mem_check(victim, sz);
+    }
+  } else {
+    /* Suspend the thread until the `atfork' handlers have completed.
+       By that time, the hooks will have been reset as well, so that
+       mALLOc() can be used again. */
+    (void)mutex_lock(&list_lock);
+    (void)mutex_unlock(&list_lock);
+    return public_mALLOc(sz);
+  }
+}
+
+static void
+free_atfork(Void_t* mem, const Void_t *caller)
+{
+  Void_t *vptr = NULL;
+  mstate ar_ptr;
+  mchunkptr p;                          /* chunk corresponding to mem */
+
+  if (mem == 0)                              /* free(0) has no effect */
+    return;
+
+  p = mem2chunk(mem);         /* do not bother to replicate free_check here */
+
+#if HAVE_MMAP
+  if (chunk_is_mmapped(p))                       /* release mmapped memory. */
+  {
+    munmap_chunk(p);
+    return;
+  }
+#endif
+
+  ar_ptr = arena_for_chunk(p);
+  tsd_getspecific(arena_key, vptr);
+  if(vptr != ATFORK_ARENA_PTR)
+    (void)mutex_lock(&ar_ptr->mutex);
+  _int_free(ar_ptr, mem);
+  if(vptr != ATFORK_ARENA_PTR)
+    (void)mutex_unlock(&ar_ptr->mutex);
+}
+
+/* The following two functions are registered via thread_atfork() to
+   make sure that the mutexes remain in a consistent state in the
+   fork()ed version of a thread.  Also adapt the malloc and free hooks
+   temporarily, because the `atfork' handler mechanism may use
+   malloc/free internally (e.g. in LinuxThreads). */
+
+static void
+ptmalloc_lock_all __MALLOC_P((void))
+{
+  mstate ar_ptr;
+
+  (void)mutex_lock(&list_lock);
+  for(ar_ptr = &main_arena;;) {
+    (void)mutex_lock(&ar_ptr->mutex);
+    ar_ptr = ar_ptr->next;
+    if(ar_ptr == &main_arena) break;
+  }
+  save_malloc_hook = __malloc_hook;
+  save_free_hook = __free_hook;
+  __malloc_hook = malloc_atfork;
+  __free_hook = free_atfork;
+  /* Only the current thread may perform malloc/free calls now. */
+  tsd_getspecific(arena_key, save_arena);
+  tsd_setspecific(arena_key, ATFORK_ARENA_PTR);
+}
+
+static void
+ptmalloc_unlock_all __MALLOC_P((void))
+{
+  mstate ar_ptr;
+
+  tsd_setspecific(arena_key, save_arena);
+  __malloc_hook = save_malloc_hook;
+  __free_hook = save_free_hook;
+  for(ar_ptr = &main_arena;;) {
+    (void)mutex_unlock(&ar_ptr->mutex);
+    ar_ptr = ar_ptr->next;
+    if(ar_ptr == &main_arena) break;
+  }
+  (void)mutex_unlock(&list_lock);
+}
+
+#ifdef __linux__
+
+/* In LinuxThreads, unlocking a mutex in the child process after a
+   fork() is currently unsafe, whereas re-initializing it is safe and
+   does not leak resources.  Therefore, a special atfork handler is
+   installed for the child. */
+
+static void
+ptmalloc_unlock_all2 __MALLOC_P((void))
+{
+  mstate ar_ptr;
+
+#if defined _LIBC || defined MALLOC_HOOKS
+  tsd_setspecific(arena_key, save_arena);
+  __malloc_hook = save_malloc_hook;
+  __free_hook = save_free_hook;
+#endif
+  for(ar_ptr = &main_arena;;) {
+    (void)mutex_init(&ar_ptr->mutex);
+    ar_ptr = ar_ptr->next;
+    if(ar_ptr == &main_arena) break;
+  }
+  (void)mutex_init(&list_lock);
+}
+
+#else
+
+#define ptmalloc_unlock_all2 ptmalloc_unlock_all
+
+#endif
+
+#endif /* !defined NO_THREADS */
+
+/* Already initialized? */
+int __malloc_initialized = -1;
+
+/* Initialization routine. */
+#ifdef _LIBC
+#include <string.h>
+extern char **_environ;
+
+static char *
+internal_function
+next_env_entry (char ***position)
+{
+  char **current = *position;
+  char *result = NULL;
+
+  while (*current != NULL)
+    {
+      if (__builtin_expect ((*current)[0] == 'M', 0)
+	  && (*current)[1] == 'A'
+	  && (*current)[2] == 'L'
+	  && (*current)[3] == 'L'
+	  && (*current)[4] == 'O'
+	  && (*current)[5] == 'C'
+	  && (*current)[6] == '_')
+	{
+	  result = &(*current)[7];
+
+	  /* Save current position for next visit.  */
+	  *position = ++current;
+
+	  break;
+	}
+
+      ++current;
+    }
+
+  return result;
+}
+#endif /* _LIBC */
+
+static void
+ptmalloc_init __MALLOC_P((void))
+{
+#if __STD_C
+  const char* s;
+#else
+  char* s;
+#endif
+  int secure = 0;
+
+  if(__malloc_initialized >= 0) return;
+  __malloc_initialized = 0;
+
+  mp_.top_pad        = DEFAULT_TOP_PAD;
+  mp_.n_mmaps_max    = DEFAULT_MMAP_MAX;
+  mp_.mmap_threshold = DEFAULT_MMAP_THRESHOLD;
+  mp_.trim_threshold = DEFAULT_TRIM_THRESHOLD;
+  mp_.pagesize       = malloc_getpagesize;
+
+#ifndef NO_THREADS
+  /* With some threads implementations, creating thread-specific data
+     or initializing a mutex may call malloc() itself.  Provide a
+     simple starter version (realloc() won't work). */
+  save_malloc_hook = __malloc_hook;
+  save_free_hook = __free_hook;
+  __malloc_hook = malloc_starter;
+  __free_hook = free_starter;
+#ifdef _LIBC
+  /* Initialize the pthreads interface. */
+  if (__pthread_initialize != NULL)
+    __pthread_initialize();
+#endif
+#endif /* !defined NO_THREADS */
+  mutex_init(&main_arena.mutex);
+  main_arena.next = &main_arena;
+
+  mutex_init(&list_lock);
+  tsd_key_create(&arena_key, NULL);
+  tsd_setspecific(arena_key, (Void_t *)&main_arena);
+  thread_atfork(ptmalloc_lock_all, ptmalloc_unlock_all, ptmalloc_unlock_all2);
+#ifndef NO_THREADS
+  __malloc_hook = save_malloc_hook;
+  __free_hook = save_free_hook;
+#endif
+#ifdef _LIBC
+  secure = __libc_enable_secure;
+  s = NULL;
+  {
+    char **runp = _environ;
+    char *envline;
+
+    while (__builtin_expect ((envline = next_env_entry (&runp)) != NULL,
+			     0))
+      {
+	size_t len = strcspn (envline, "=");
+
+	if (envline[len] != '=')
+	  /* This is a "MALLOC_" variable at the end of the string
+	     without a '=' character.  Ignore it since otherwise we
+	     will access invalid memory below.  */
+	  continue;
+
+	switch (len)
+	  {
+	  case 6:
+	    if (memcmp (envline, "CHECK_", 6) == 0)
+	      s = &envline[7];
+	    break;
+	  case 8:
+	    if (! secure && memcmp (envline, "TOP_PAD_", 8) == 0)
+	      mALLOPt(M_TOP_PAD, atoi(&envline[9]));
+	    break;
+	  case 9:
+	    if (! secure && memcmp (envline, "MMAP_MAX_", 9) == 0)
+	      mALLOPt(M_MMAP_MAX, atoi(&envline[10]));
+	    break;
+	  case 15:
+	    if (! secure)
+	      {
+		if (memcmp (envline, "TRIM_THRESHOLD_", 15) == 0)
+		  mALLOPt(M_TRIM_THRESHOLD, atoi(&envline[16]));
+		else if (memcmp (envline, "MMAP_THRESHOLD_", 15) == 0)
+		  mALLOPt(M_MMAP_THRESHOLD, atoi(&envline[16]));
+	      }
+	    break;
+	  default:
+	    break;
+	  }
+      }
+  }
+#else
+  if (! secure)
+    {
+      if((s = getenv("MALLOC_TRIM_THRESHOLD_")))
+	mALLOPt(M_TRIM_THRESHOLD, atoi(s));
+      if((s = getenv("MALLOC_TOP_PAD_")))
+	mALLOPt(M_TOP_PAD, atoi(s));
+      if((s = getenv("MALLOC_MMAP_THRESHOLD_")))
+	mALLOPt(M_MMAP_THRESHOLD, atoi(s));
+      if((s = getenv("MALLOC_MMAP_MAX_")))
+	mALLOPt(M_MMAP_MAX, atoi(s));
+    }
+  s = getenv("MALLOC_CHECK_");
+#endif
+  if(s) {
+    if(s[0]) mALLOPt(M_CHECK_ACTION, (int)(s[0] - '0'));
+    __malloc_check_init();
+  }
+  if(__malloc_initialize_hook != NULL)
+    (*__malloc_initialize_hook)();
+  __malloc_initialized = 1;
+}
+
+/* There are platforms (e.g. Hurd) with a link-time hook mechanism. */
+#ifdef thread_atfork_static
+thread_atfork_static(ptmalloc_lock_all, ptmalloc_unlock_all, \
+                     ptmalloc_unlock_all2)
+#endif
+
+
+
+/* Managing heaps and arenas (for concurrent threads) */
+
+#if USE_ARENAS
+
+#if MALLOC_DEBUG > 1
+
+/* Print the complete contents of a single heap to stderr. */
+
+static void
+#if __STD_C
+dump_heap(heap_info *heap)
+#else
+dump_heap(heap) heap_info *heap;
+#endif
+{
+  char *ptr;
+  mchunkptr p;
+
+  fprintf(stderr, "Heap %p, size %10lx:\n", heap, (long)heap->size);
+  ptr = (heap->ar_ptr != (mstate)(heap+1)) ?
+    (char*)(heap + 1) : (char*)(heap + 1) + sizeof(struct malloc_state);
+  p = (mchunkptr)(((unsigned long)ptr + MALLOC_ALIGN_MASK) &
+                  ~MALLOC_ALIGN_MASK);
+  for(;;) {
+    fprintf(stderr, "chunk %p size %10lx", p, (long)p->size);
+    if(p == top(heap->ar_ptr)) {
+      fprintf(stderr, " (top)\n");
+      break;
+    } else if(p->size == (0|PREV_INUSE)) {
+      fprintf(stderr, " (fence)\n");
+      break;
+    }
+    fprintf(stderr, "\n");
+    p = next_chunk(p);
+  }
+}
+
+#endif /* MALLOC_DEBUG > 1 */
+
+/* Create a new heap.  size is automatically rounded up to a multiple
+   of the page size. */
+
+static heap_info *
+internal_function
+#if __STD_C
+new_heap(size_t size, size_t top_pad)
+#else
+new_heap(size, top_pad) size_t size, top_pad;
+#endif
+{
+  size_t page_mask = malloc_getpagesize - 1;
+  char *p1, *p2;
+  unsigned long ul;
+  heap_info *h;
+
+  if(size+top_pad < HEAP_MIN_SIZE)
+    size = HEAP_MIN_SIZE;
+  else if(size+top_pad <= HEAP_MAX_SIZE)
+    size += top_pad;
+  else if(size > HEAP_MAX_SIZE)
+    return 0;
+  else
+    size = HEAP_MAX_SIZE;
+  size = (size + page_mask) & ~page_mask;
+
+  /* A memory region aligned to a multiple of HEAP_MAX_SIZE is needed.
+     No swap space needs to be reserved for the following large
+     mapping (on Linux, this is the case for all non-writable mappings
+     anyway). */
+  p1 = (char *)MMAP(0, HEAP_MAX_SIZE<<1, PROT_NONE, MAP_PRIVATE|MAP_NORESERVE);
+  if(p1 != MAP_FAILED) {
+    p2 = (char *)(((unsigned long)p1 + (HEAP_MAX_SIZE-1)) & ~(HEAP_MAX_SIZE-1));
+    ul = p2 - p1;
+    munmap(p1, ul);
+    munmap(p2 + HEAP_MAX_SIZE, HEAP_MAX_SIZE - ul);
+  } else {
+    /* Try to take the chance that an allocation of only HEAP_MAX_SIZE
+       is already aligned. */
+    p2 = (char *)MMAP(0, HEAP_MAX_SIZE, PROT_NONE, MAP_PRIVATE|MAP_NORESERVE);
+    if(p2 == MAP_FAILED)
+      return 0;
+    if((unsigned long)p2 & (HEAP_MAX_SIZE-1)) {
+      munmap(p2, HEAP_MAX_SIZE);
+      return 0;
+    }
+  }
+  if(mprotect(p2, size, PROT_READ|PROT_WRITE) != 0) {
+    munmap(p2, HEAP_MAX_SIZE);
+    return 0;
+  }
+  h = (heap_info *)p2;
+  h->size = size;
+  THREAD_STAT(stat_n_heaps++);
+  return h;
+}
+
+/* Grow or shrink a heap.  size is automatically rounded up to a
+   multiple of the page size if it is positive. */
+
+static int
+#if __STD_C
+grow_heap(heap_info *h, long diff)
+#else
+grow_heap(h, diff) heap_info *h; long diff;
+#endif
+{
+  size_t page_mask = malloc_getpagesize - 1;
+  long new_size;
+
+  if(diff >= 0) {
+    diff = (diff + page_mask) & ~page_mask;
+    new_size = (long)h->size + diff;
+    if(new_size > HEAP_MAX_SIZE)
+      return -1;
+    if(mprotect((char *)h + h->size, diff, PROT_READ|PROT_WRITE) != 0)
+      return -2;
+  } else {
+    new_size = (long)h->size + diff;
+    if(new_size < (long)sizeof(*h))
+      return -1;
+    /* Try to re-map the extra heap space freshly to save memory, and
+       make it inaccessible. */
+    if((char *)MMAP((char *)h + new_size, -diff, PROT_NONE,
+                    MAP_PRIVATE|MAP_FIXED) == (char *) MAP_FAILED)
+      return -2;
+    /*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/
+  }
+  h->size = new_size;
+  return 0;
+}
+
+/* Delete a heap. */
+
+#define delete_heap(heap) munmap((char*)(heap), HEAP_MAX_SIZE)
+
+static int
+internal_function
+#if __STD_C
+heap_trim(heap_info *heap, size_t pad)
+#else
+heap_trim(heap, pad) heap_info *heap; size_t pad;
+#endif
+{
+  mstate ar_ptr = heap->ar_ptr;
+  unsigned long pagesz = mp_.pagesize;
+  mchunkptr top_chunk = top(ar_ptr), p, bck, fwd;
+  heap_info *prev_heap;
+  long new_size, top_size, extra;
+
+  /* Can this heap go away completely? */
+  while(top_chunk == chunk_at_offset(heap, sizeof(*heap))) {
+    prev_heap = heap->prev;
+    p = chunk_at_offset(prev_heap, prev_heap->size - (MINSIZE-2*SIZE_SZ));
+    assert(p->size == (0|PREV_INUSE)); /* must be fencepost */
+    p = prev_chunk(p);
+    new_size = chunksize(p) + (MINSIZE-2*SIZE_SZ);
+    assert(new_size>0 && new_size<(long)(2*MINSIZE));
+    if(!prev_inuse(p))
+      new_size += p->prev_size;
+    assert(new_size>0 && new_size<HEAP_MAX_SIZE);
+    if(new_size + (HEAP_MAX_SIZE - prev_heap->size) < pad + MINSIZE + pagesz)
+      break;
+    ar_ptr->system_mem -= heap->size;
+    arena_mem -= heap->size;
+    delete_heap(heap);
+    heap = prev_heap;
+    if(!prev_inuse(p)) { /* consolidate backward */
+      p = prev_chunk(p);
+      unlink(p, bck, fwd);
+    }
+    assert(((unsigned long)((char*)p + new_size) & (pagesz-1)) == 0);
+    assert( ((char*)p + new_size) == ((char*)heap + heap->size) );
+    top(ar_ptr) = top_chunk = p;
+    set_head(top_chunk, new_size | PREV_INUSE);
+    /*check_chunk(ar_ptr, top_chunk);*/
+  }
+  top_size = chunksize(top_chunk);
+  extra = ((top_size - pad - MINSIZE + (pagesz-1))/pagesz - 1) * pagesz;
+  if(extra < (long)pagesz)
+    return 0;
+  /* Try to shrink. */
+  if(grow_heap(heap, -extra) != 0)
+    return 0;
+  ar_ptr->system_mem -= extra;
+  arena_mem -= extra;
+
+  /* Success. Adjust top accordingly. */
+  set_head(top_chunk, (top_size - extra) | PREV_INUSE);
+  /*check_chunk(ar_ptr, top_chunk);*/
+  return 1;
+}
+
+static mstate
+internal_function
+#if __STD_C
+arena_get2(mstate a_tsd, size_t size)
+#else
+arena_get2(a_tsd, size) mstate a_tsd; size_t size;
+#endif
+{
+  mstate a;
+  int err;
+
+  if(!a_tsd)
+    a = a_tsd = &main_arena;
+  else {
+    a = a_tsd->next;
+    if(!a) {
+      /* This can only happen while initializing the new arena. */
+      (void)mutex_lock(&main_arena.mutex);
+      THREAD_STAT(++(main_arena.stat_lock_wait));
+      return &main_arena;
+    }
+  }
+
+  /* Check the global, circularly linked list for available arenas. */
+ repeat:
+  do {
+    if(!mutex_trylock(&a->mutex)) {
+      THREAD_STAT(++(a->stat_lock_loop));
+      tsd_setspecific(arena_key, (Void_t *)a);
+      return a;
+    }
+    a = a->next;
+  } while(a != a_tsd);
+
+  /* If not even the list_lock can be obtained, try again.  This can
+     happen during `atfork', or for example on systems where thread
+     creation makes it temporarily impossible to obtain _any_
+     locks. */
+  if(mutex_trylock(&list_lock)) {
+    a = a_tsd;
+    goto repeat;
+  }
+  (void)mutex_unlock(&list_lock);
+
+  /* Nothing immediately available, so generate a new arena.  */
+  a = _int_new_arena(size);
+  if(!a)
+    return 0;
+
+  tsd_setspecific(arena_key, (Void_t *)a);
+  mutex_init(&a->mutex);
+  err = mutex_lock(&a->mutex); /* remember result */
+
+  /* Add the new arena to the global list.  */
+  (void)mutex_lock(&list_lock);
+  a->next = main_arena.next;
+  main_arena.next = a;
+  (void)mutex_unlock(&list_lock);
+
+  if(err) /* locking failed; keep arena for further attempts later */
+    return 0;
+
+  THREAD_STAT(++(a->stat_lock_loop));
+  return a;
+}
+
+/* Create a new arena with initial size "size".  */
+
+mstate
+_int_new_arena(size_t size)
+{
+  mstate a;
+  heap_info *h;
+  char *ptr;
+  unsigned long misalign;
+
+  h = new_heap(size + (sizeof(*h) + sizeof(*a) + MALLOC_ALIGNMENT),
+	       mp_.top_pad);
+  if(!h) {
+    /* Maybe size is too large to fit in a single heap.  So, just try
+       to create a minimally-sized arena and let _int_malloc() attempt
+       to deal with the large request via mmap_chunk().  */
+    h = new_heap(sizeof(*h) + sizeof(*a) + MALLOC_ALIGNMENT, mp_.top_pad);
+    if(!h)
+      return 0;
+  }
+  a = h->ar_ptr = (mstate)(h+1);
+  malloc_init_state(a);
+  /*a->next = NULL;*/
+  a->system_mem = a->max_system_mem = h->size;
+  arena_mem += h->size;
+#ifdef NO_THREADS
+  if((unsigned long)(mp_.mmapped_mem + arena_mem + main_arena.system_mem) >
+     mp_.max_total_mem)
+    mp_.max_total_mem = mp_.mmapped_mem + arena_mem + main_arena.system_mem;
+#endif
+
+  /* Set up the top chunk, with proper alignment. */
+  ptr = (char *)(a + 1);
+  misalign = (unsigned long)chunk2mem(ptr) & MALLOC_ALIGN_MASK;
+  if (misalign > 0)
+    ptr += MALLOC_ALIGNMENT - misalign;
+  top(a) = (mchunkptr)ptr;
+  set_head(top(a), (((char*)h + h->size) - ptr) | PREV_INUSE);
+
+  return a;
+}
+
+#endif /* USE_ARENAS */
+
+/*
+ * Local variables:
+ * c-basic-offset: 2
+ * End:
+ */