arena.c

一个很好的内存泄露的监测代码

/* 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 <[e-mail]>, 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: arena.c,v 1.9 2004/11/05 14:42:23 wg Exp $ */

/* 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;

/* Already initialized? */
int __malloc_initialized = -1;

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

#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));
# if !defined _LIBC || !defined USE_TLS || (defined SHARED && !USE___THREAD)
static __malloc_ptr_t (*save_memalign_hook) __MALLOC_P ((size_t __align,
							 size_t __size,
						       __const __malloc_ptr_t));
# endif
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;

  if(__malloc_initialized < 1)
    return;
  (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;

  if(__malloc_initialized < 1)
    return;
  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(__malloc_initialized < 1)
    return;
#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 */

/* 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 */

/* Set up basic state so that _int_malloc et al can work.  */
static void
ptmalloc_init_minimal __MALLOC_P((void))
{
#if DEFAULT_TOP_PAD != 0
  mp_.top_pad        = DEFAULT_TOP_PAD;
#endif
  mp_.n_mmaps_max    = DEFAULT_MMAP_MAX;
  mp_.mmap_threshold = DEFAULT_MMAP_THRESHOLD;
  mp_.trim_threshold = DEFAULT_TRIM_THRESHOLD;
  mp_.pagesize       = malloc_getpagesize;
}


#if !(USE_STARTER & 2)
static
#endif
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;

  if (mp_.pagesize == 0)
    ptmalloc_init_minimal();

#ifndef NO_THREADS
# if USE_STARTER & 1
  /* 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_memalign_hook = __memalign_hook;
  save_free_hook = __free_hook;
  __malloc_hook = malloc_starter;
  __memalign_hook = memalign_starter;
  __free_hook = free_starter;
#  ifdef _LIBC
  /* Initialize the pthreads interface. */
  if (__pthread_initialize != NULL)
    __pthread_initialize();
#  endif /* !defined _LIBC */
# endif /* USE_STARTER & 1 */
#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
# if USE_STARTER & 1
  __malloc_hook = save_malloc_hook;
  __memalign_hook = save_memalign_hook;
  __free_hook = save_free_hook;
# endif
# if USE_STARTER & 2
  __malloc_hook = 0;
  __memalign_hook = 0;
  __free_hook = 0;
# endif
#endif
#ifdef _LIBC
  secure = __libc_enable_secure;