/* Malloc implementation for multiple threads without lock contention.

   Copyright (C) 2001-2018 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 Lesser General Public License as

   published by the Free Software Foundation; either version 2.1 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; see the file COPYING.LIB.  If

   not, see <http://www.gnu.org/licenses/>.  */

#include <stdbool.h>

#if HAVE_TUNABLES

# define TUNABLE_NAMESPACE malloc

#endif

#include <elf/dl-tunables.h>

/* Compile-time constants.  */

#define HEAP_MIN_SIZE (32 * 1024)

#ifndef HEAP_MAX_SIZE

# ifdef DEFAULT_MMAP_THRESHOLD_MAX

#  define HEAP_MAX_SIZE (2 * DEFAULT_MMAP_THRESHOLD_MAX)

# else

#  define HEAP_MAX_SIZE (1024 * 1024) /* must be a power of two */

# endif

#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.  */

/***************************************************************************/

#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.  */

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 mprotect_size; /* Size in bytes that has been mprotected

                           PROT_READ|PROT_WRITE.  */

  /* Make sure the following data is properly aligned, particularly

     that sizeof (heap_info) + 2 * SIZE_SZ is a multiple of

     MALLOC_ALIGNMENT. */

  char pad[-6 * SIZE_SZ & MALLOC_ALIGN_MASK];

} heap_info;

/* Get a compile-time error if the heap_info padding is not correct

   to make alignment work as expected in sYSMALLOc.  */

extern int sanity_check_heap_info_alignment[(sizeof (heap_info)

                                             + 2 * SIZE_SZ) % MALLOC_ALIGNMENT

                                            ? -1 : 1];

/* Thread specific data.  */

static __thread mstate thread_arena attribute_tls_model_ie;

/* Arena free list.  free_list_lock synchronizes access to the

   free_list variable below, and the next_free and attached_threads

   members of struct malloc_state objects.  No other locks must be

   acquired after free_list_lock has been acquired.  */

__libc_lock_define_initialized (static, free_list_lock);

static size_t narenas = 1;

static mstate free_list;

/* list_lock prevents concurrent writes to the next member of struct

   malloc_state objects.

   Read access to the next member is supposed to synchronize with the

   atomic_write_barrier and the write to the next member in

   _int_new_arena.  This suffers from data races; see the FIXME

   comments in _int_new_arena and reused_arena.

   list_lock also prevents concurrent forks.  At the time list_lock is

   acquired, no arena lock must have been acquired, but it is

   permitted to acquire arena locks subsequently, while list_lock is

   acquired.  */

__libc_lock_define_initialized (static, list_lock);

/* Already initialized? */

int __malloc_initialized = -1;

/**************************************************************************/

/* 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 { \

      ptr = thread_arena;						      \

      arena_lock (ptr, size);						      \

  } while (0)

#define arena_lock(ptr, size) do {					      \

      if (ptr)								      \

        __libc_lock_lock (ptr->mutex);					      \

      else								      \

        ptr = arena_get2 ((size), NULL);				      \

  } 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_main_arena (ptr) ? &main_arena : heap_for_ptr (ptr)->ar_ptr)

/**************************************************************************/

/* atfork support.  */

/* The following three functions are called around fork from a

   multi-threaded process.  We do not use the general fork handler

   mechanism to make sure that our handlers are the last ones being

   called, so that other fork handlers can use the malloc

   subsystem.  */

void

__malloc_fork_lock_parent (void)

{

  if (__malloc_initialized < 1)

    return;

  /* We do not acquire free_list_lock here because we completely

     reconstruct free_list in __malloc_fork_unlock_child.  */

  __libc_lock_lock (list_lock);

  for (mstate ar_ptr = &main_arena;; )

    {

      __libc_lock_lock (ar_ptr->mutex);

      ar_ptr = ar_ptr->next;

      if (ar_ptr == &main_arena)

        break;

    }

}

void

__malloc_fork_unlock_parent (void)

{

  if (__malloc_initialized < 1)

    return;

  for (mstate ar_ptr = &main_arena;; )

    {

      __libc_lock_unlock (ar_ptr->mutex);

      ar_ptr = ar_ptr->next;

      if (ar_ptr == &main_arena)

        break;

    }

  __libc_lock_unlock (list_lock);

}

void

__malloc_fork_unlock_child (void)

{

  if (__malloc_initialized < 1)

    return;

  /* Push all arenas to the free list, except thread_arena, which is

     attached to the current thread.  */

  __libc_lock_init (free_list_lock);

  if (thread_arena != NULL)

    thread_arena->attached_threads = 1;

  free_list = NULL;

  for (mstate ar_ptr = &main_arena;; )

    {

      __libc_lock_init (ar_ptr->mutex);

      if (ar_ptr != thread_arena)

        {

	  /* This arena is no longer attached to any thread.  */

	  ar_ptr->attached_threads = 0;

          ar_ptr->next_free = free_list;

          free_list = ar_ptr;

        }

      ar_ptr = ar_ptr->next;

      if (ar_ptr == &main_arena)

        break;

    }

  __libc_lock_init (list_lock);

}

#if HAVE_TUNABLES

static inline int do_set_mallopt_check (int32_t value);

void

TUNABLE_CALLBACK (set_mallopt_check) (tunable_val_t *valp)

{

  int32_t value = (int32_t) valp->numval;

  if (value != 0)

    __malloc_check_init ();

}

# define TUNABLE_CALLBACK_FNDECL(__name, __type) \

static inline int do_ ## __name (__type value);				      \

void									      \

TUNABLE_CALLBACK (__name) (tunable_val_t *valp)				      \

{									      \

  __type value = (__type) (valp)->numval;				      \

  do_ ## __name (value);						      \

}

TUNABLE_CALLBACK_FNDECL (set_mmap_threshold, size_t)

TUNABLE_CALLBACK_FNDECL (set_mmaps_max, int32_t)

TUNABLE_CALLBACK_FNDECL (set_top_pad, size_t)

TUNABLE_CALLBACK_FNDECL (set_perturb_byte, int32_t)

TUNABLE_CALLBACK_FNDECL (set_trim_threshold, size_t)

TUNABLE_CALLBACK_FNDECL (set_arena_max, size_t)

TUNABLE_CALLBACK_FNDECL (set_arena_test, size_t)

#if USE_TCACHE

TUNABLE_CALLBACK_FNDECL (set_tcache_max, size_t)

TUNABLE_CALLBACK_FNDECL (set_tcache_count, size_t)

TUNABLE_CALLBACK_FNDECL (set_tcache_unsorted_limit, size_t)

#endif

#else

/* Initialization routine. */

#include <string.h>

extern char **_environ;

static char *

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

#ifdef SHARED

static void *

__failing_morecore (ptrdiff_t d)

{

  return (void *) MORECORE_FAILURE;

}

extern struct dl_open_hook *_dl_open_hook;

libc_hidden_proto (_dl_open_hook);

#endif

static void

ptmalloc_init (void)

{

  if (__malloc_initialized >= 0)

    return;

  __malloc_initialized = 0;

#ifdef SHARED

  /* In case this libc copy is in a non-default namespace, never use brk.

     Likewise if dlopened from statically linked program.  */

  Dl_info di;

  struct link_map *l;

  if (_dl_open_hook != NULL

      || (_dl_addr (ptmalloc_init, &di, &l, NULL) != 0

          && l->l_ns != LM_ID_BASE))

    __morecore = __failing_morecore;

#endif

  thread_arena = &main_arena;

  malloc_init_state (&main_arena);

#if HAVE_TUNABLES

  TUNABLE_GET (check, int32_t, TUNABLE_CALLBACK (set_mallopt_check));

  TUNABLE_GET (top_pad, size_t, TUNABLE_CALLBACK (set_top_pad));

  TUNABLE_GET (perturb, int32_t, TUNABLE_CALLBACK (set_perturb_byte));

  TUNABLE_GET (mmap_threshold, size_t, TUNABLE_CALLBACK (set_mmap_threshold));

  TUNABLE_GET (trim_threshold, size_t, TUNABLE_CALLBACK (set_trim_threshold));

  TUNABLE_GET (mmap_max, int32_t, TUNABLE_CALLBACK (set_mmaps_max));

  TUNABLE_GET (arena_max, size_t, TUNABLE_CALLBACK (set_arena_max));

  TUNABLE_GET (arena_test, size_t, TUNABLE_CALLBACK (set_arena_test));

# if USE_TCACHE

  TUNABLE_GET (tcache_max, size_t, TUNABLE_CALLBACK (set_tcache_max));

  TUNABLE_GET (tcache_count, size_t, TUNABLE_CALLBACK (set_tcache_count));

  TUNABLE_GET (tcache_unsorted_limit, size_t,

	       TUNABLE_CALLBACK (set_tcache_unsorted_limit));

# endif

#else

  const char *s = NULL;

  if (__glibc_likely (_environ != 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 (!__builtin_expect (__libc_enable_secure, 0))

                {

                  if (memcmp (envline, "TOP_PAD_", 8) == 0)

                    __libc_mallopt (M_TOP_PAD, atoi (&envline[9]));

                  else if (memcmp (envline, "PERTURB_", 8) == 0)

                    __libc_mallopt (M_PERTURB, atoi (&envline[9]));

                }

              break;

            case 9:

              if (!__builtin_expect (__libc_enable_secure, 0))

                {

                  if (memcmp (envline, "MMAP_MAX_", 9) == 0)

                    __libc_mallopt (M_MMAP_MAX, atoi (&envline[10]));

                  else if (memcmp (envline, "ARENA_MAX", 9) == 0)

                    __libc_mallopt (M_ARENA_MAX, atoi (&envline[10]));

                }

              break;

            case 10:

              if (!__builtin_expect (__libc_enable_secure, 0))

                {

                  if (memcmp (envline, "ARENA_TEST", 10) == 0)

                    __libc_mallopt (M_ARENA_TEST, atoi (&envline[11]));

                }

              break;

            case 15:

              if (!__builtin_expect (__libc_enable_secure, 0))

                {

                  if (memcmp (envline, "TRIM_THRESHOLD_", 15) == 0)

                    __libc_mallopt (M_TRIM_THRESHOLD, atoi (&envline[16]));

                  else if (memcmp (envline, "MMAP_THRESHOLD_", 15) == 0)

                    __libc_mallopt (M_MMAP_THRESHOLD, atoi (&envline[16]));

                }

              break;

            default:

              break;

            }

        }

    }

  if (s && s[0] != '\0' && s[0] != '0')

    __malloc_check_init ();

#endif

#if HAVE_MALLOC_INIT_HOOK

  void (*hook) (void) = atomic_forced_read (__malloc_initialize_hook);

  if (hook != NULL)

    (*hook)();

#endif

  __malloc_initialized = 1;

}

/* Managing heaps and arenas (for concurrent threads) */

#if MALLOC_DEBUG > 1

/* Print the complete contents of a single heap to stderr. */

static void

dump_heap (heap_info *heap)

{

  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 */

/* If consecutive mmap (0, HEAP_MAX_SIZE << 1, ...) calls return decreasing

   addresses as opposed to increasing, new_heap would badly fragment the

   address space.  In that case remember the second HEAP_MAX_SIZE part

   aligned to HEAP_MAX_SIZE from last mmap (0, HEAP_MAX_SIZE << 1, ...)

   call (if it is already aligned) and try to reuse it next time.  We need

   no locking for it, as kernel ensures the atomicity for us - worst case

   we'll call mmap (addr, HEAP_MAX_SIZE, ...) for some value of addr in

   multiple threads, but only one will succeed.  */

static char *aligned_heap_area;

/* Create a new heap.  size is automatically rounded up to a multiple

   of the page size. */

static heap_info *

new_heap (size_t size, size_t top_pad)

{

  size_t pagesize = GLRO (dl_pagesize);

  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 = ALIGN_UP (size, pagesize);

  /* 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). */

  p2 = MAP_FAILED;

  if (aligned_heap_area)

    {

      p2 = (char *) MMAP (aligned_heap_area, HEAP_MAX_SIZE, PROT_NONE,

                          MAP_NORESERVE);

      aligned_heap_area = NULL;

      if (p2 != MAP_FAILED && ((unsigned long) p2 & (HEAP_MAX_SIZE - 1)))

        {

          __munmap (p2, HEAP_MAX_SIZE);

          p2 = MAP_FAILED;

        }

    }

  if (p2 == MAP_FAILED)

    {

      p1 = (char *) MMAP (0, HEAP_MAX_SIZE << 1, PROT_NONE, MAP_NORESERVE);

      if (p1 != MAP_FAILED)

        {

          p2 = (char *) (((unsigned long) p1 + (HEAP_MAX_SIZE - 1))

                         & ~(HEAP_MAX_SIZE - 1));

          ul = p2 - p1;

          if (ul)

            __munmap (p1, ul);

          else

            aligned_heap_area = p2 + HEAP_MAX_SIZE;

          __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_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;

  h->mprotect_size = size;

  LIBC_PROBE (memory_heap_new, 2, h, h->size);

  return h;

}

/* Grow a heap.  size is automatically rounded up to a

   multiple of the page size. */

static int

grow_heap (heap_info *h, long diff)

{

  size_t pagesize = GLRO (dl_pagesize);

  long new_size;

  diff = ALIGN_UP (diff, pagesize);

  new_size = (long) h->size + diff;

  if ((unsigned long) new_size > (unsigned long) HEAP_MAX_SIZE)

    return -1;

  if ((unsigned long) new_size > h->mprotect_size)

    {

      if (__mprotect ((char *) h + h->mprotect_size,

                      (unsigned long) new_size - h->mprotect_size,

                      PROT_READ | PROT_WRITE) != 0)

        return -2;

      h->mprotect_size = new_size;

    }

  h->size = new_size;

  LIBC_PROBE (memory_heap_more, 2, h, h->size);

  return 0;

}

/* Shrink a heap.  */

static int

shrink_heap (heap_info *h, long diff)

{

  long new_size;

  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.  See malloc-sysdep.h to know when this is true.  */

  if (__glibc_unlikely (check_may_shrink_heap ()))

    {

      if ((char *) MMAP ((char *) h + new_size, diff, PROT_NONE,

                         MAP_FIXED) == (char *) MAP_FAILED)

        return -2;

      h->mprotect_size = new_size;

    }

  else

    __madvise ((char *) h + new_size, diff, MADV_DONTNEED);

  /*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/

  h->size = new_size;

  LIBC_PROBE (memory_heap_less, 2, h, h->size);

  return 0;

}

/* Delete a heap. */

#define delete_heap(heap) \

  do {									      \

      if ((char *) (heap) + HEAP_MAX_SIZE == aligned_heap_area)		      \

        aligned_heap_area = NULL;					      \

      __munmap ((char *) (heap), HEAP_MAX_SIZE);			      \

    } while (0)

static int

heap_trim (heap_info *heap, size_t pad)

{

  mstate ar_ptr = heap->ar_ptr;

  unsigned long pagesz = GLRO (dl_pagesize);

  mchunkptr top_chunk = top (ar_ptr), p;

  heap_info *prev_heap;

  long new_size, top_size, top_area, extra, prev_size, misalign;

  /* Can this heap go away completely? */

  while (top_chunk == chunk_at_offset (heap, sizeof (*heap)))

    {

      prev_heap = heap->prev;

      prev_size = prev_heap->size - (MINSIZE - 2 * SIZE_SZ);

      p = chunk_at_offset (prev_heap, prev_size);

      /* fencepost must be properly aligned.  */

      misalign = ((long) p) & MALLOC_ALIGN_MASK;

      p = chunk_at_offset (prev_heap, prev_size - misalign);

      assert (chunksize_nomask (p) == (0 | PREV_INUSE)); /* must be fencepost */

      p = prev_chunk (p);

      new_size = chunksize (p) + (MINSIZE - 2 * SIZE_SZ) + misalign;

      assert (new_size > 0 && new_size < (long) (2 * MINSIZE));

      if (!prev_inuse (p))

        new_size += prev_size (p);

      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;

      LIBC_PROBE (memory_heap_free, 2, heap, heap->size);

      delete_heap (heap);

      heap = prev_heap;

      if (!prev_inuse (p)) /* consolidate backward */

        {

          p = prev_chunk (p);

          unlink_chunk (ar_ptr, p);

        }

      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);*/

    }

  /* Uses similar logic for per-thread arenas as the main arena with systrim

     and _int_free by preserving the top pad and rounding down to the nearest

     page.  */

  top_size = chunksize (top_chunk);

  if ((unsigned long)(top_size) <

      (unsigned long)(mp_.trim_threshold))

    return 0;

  top_area = top_size - MINSIZE - 1;

  if (top_area < 0 || (size_t) top_area <= pad)

    return 0;

  /* Release in pagesize units and round down to the nearest page.  */

  extra = ALIGN_DOWN(top_area - pad, pagesz);

  if (extra == 0)

    return 0;

  /* Try to shrink. */

  if (shrink_heap (heap, extra) != 0)

    return 0;

  ar_ptr->system_mem -= extra;

  /* Success. Adjust top accordingly. */

  set_head (top_chunk, (top_size - extra) | PREV_INUSE);

  /*check_chunk(ar_ptr, top_chunk);*/

  return 1;

}

/* Create a new arena with initial size "size".  */

/* If REPLACED_ARENA is not NULL, detach it from this thread.  Must be

   called while free_list_lock is held.  */

static void

detach_arena (mstate replaced_arena)

{

  if (replaced_arena != NULL)

    {

      assert (replaced_arena->attached_threads > 0);

      /* The current implementation only detaches from main_arena in

	 case of allocation failure.  This means that it is likely not

	 beneficial to put the arena on free_list even if the

	 reference count reaches zero.  */

      --replaced_arena->attached_threads;

    }

}

static 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->attached_threads = 1;

  /*a->next = NULL;*/

  a->system_mem = a->max_system_mem = h->size;

  /* 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);

  LIBC_PROBE (memory_arena_new, 2, a, size);

  mstate replaced_arena = thread_arena;

  thread_arena = a;

  __libc_lock_init (a->mutex);

  __libc_lock_lock (list_lock);

  /* Add the new arena to the global list.  */

  a->next = main_arena.next;

  /* FIXME: The barrier is an attempt to synchronize with read access

     in reused_arena, which does not acquire list_lock while

     traversing the list.  */

  atomic_write_barrier ();

  main_arena.next = a;

  __libc_lock_unlock (list_lock);

  __libc_lock_lock (free_list_lock);

  detach_arena (replaced_arena);

  __libc_lock_unlock (free_list_lock);

  /* Lock this arena.  NB: Another thread may have been attached to

     this arena because the arena is now accessible from the

     main_arena.next list and could have been picked by reused_arena.

     This can only happen for the last arena created (before the arena

     limit is reached).  At this point, some arena has to be attached

     to two threads.  We could acquire the arena lock before list_lock

     to make it less likely that reused_arena picks this new arena,

     but this could result in a deadlock with

     __malloc_fork_lock_parent.  */

  __libc_lock_lock (a->mutex);

  return a;

}

/* Remove an arena from free_list.  */

static mstate

get_free_list (void)

{

  mstate replaced_arena = thread_arena;

  mstate result = free_list;

  if (result != NULL)

    {

      __libc_lock_lock (free_list_lock);

      result = free_list;

      if (result != NULL)

	{

	  free_list = result->next_free;

	  /* The arena will be attached to this thread.  */

	  assert (result->attached_threads == 0);

	  result->attached_threads = 1;

	  detach_arena (replaced_arena);

	}

      __libc_lock_unlock (free_list_lock);

      if (result != NULL)

        {

          LIBC_PROBE (memory_arena_reuse_free_list, 1, result);

          __libc_lock_lock (result->mutex);

	  thread_arena = result;

        }

    }

  return result;

}

/* Remove the arena from the free list (if it is present).

   free_list_lock must have been acquired by the caller.  */

static void

remove_from_free_list (mstate arena)

{

  mstate *previous = &free_list;

  for (mstate p = free_list; p != NULL; p = p->next_free)

    {

      assert (p->attached_threads == 0);

      if (p == arena)

	{

	  /* Remove the requested arena from the list.  */

	  *previous = p->next_free;

	  break;

	}

      else

	previous = &p->next_free;

    }

}

/* Lock and return an arena that can be reused for memory allocation.

   Avoid AVOID_ARENA as we have already failed to allocate memory in

   it and it is currently locked.  */

static mstate

reused_arena (mstate avoid_arena)

{

  mstate result;

  /* FIXME: Access to next_to_use suffers from data races.  */

  static mstate next_to_use;

  if (next_to_use == NULL)

    next_to_use = &main_arena;

  /* Iterate over all arenas (including those linked from

     free_list).  */

  result = next_to_use;

  do

    {

      if (!__libc_lock_trylock (result->mutex))

        goto out;

      /* FIXME: This is a data race, see _int_new_arena.  */

      result = result->next;

    }

  while (result != next_to_use);

  /* Avoid AVOID_ARENA as we have already failed to allocate memory

     in that arena and it is currently locked.   */

  if (result == avoid_arena)

    result = result->next;

  /* No arena available without contention.  Wait for the next in line.  */

  LIBC_PROBE (memory_arena_reuse_wait, 3, &result->mutex, result, avoid_arena);

  __libc_lock_lock (result->mutex);

out:

  /* Attach the arena to the current thread.  */

  {

    /* Update the arena thread attachment counters.   */

    mstate replaced_arena = thread_arena;

    __libc_lock_lock (free_list_lock);

    detach_arena (replaced_arena);

    /* We may have picked up an arena on the free list.  We need to

       preserve the invariant that no arena on the free list has a

       positive attached_threads counter (otherwise,

       arena_thread_freeres cannot use the counter to determine if the

       arena needs to be put on the free list).  We unconditionally

       remove the selected arena from the free list.  The caller of

       reused_arena checked the free list and observed it to be empty,

       so the list is very short.  */

    remove_from_free_list (result);

    ++result->attached_threads;

    __libc_lock_unlock (free_list_lock);

  }

  LIBC_PROBE (memory_arena_reuse, 2, result, avoid_arena);

  thread_arena = result;

  next_to_use = result->next;

  return result;

}

static mstate

arena_get2 (size_t size, mstate avoid_arena)

{

  mstate a;

  static size_t narenas_limit;

  a = get_free_list ();

  if (a == NULL)

    {