text: #include "jemalloc/internal/jemalloc_internal.h"
  #ifndef JEMALLOC_ZONE
  #  error "This source file is for zones on Darwin (OS X)."
  #endif
  
  /*
   * The malloc_default_purgeable_zone function is only available on >= 10.6.
   * We need to check whether it is present at runtime, thus the weak_import.
   */
  extern malloc_zone_t *malloc_default_purgeable_zone(void)
  JEMALLOC_ATTR(weak_import);
  
  /******************************************************************************/
  /* Data. */
  
  static malloc_zone_t zone;
  static struct malloc_introspection_t zone_introspect;
  
  /******************************************************************************/
  /* Function prototypes for non-inline static functions. */
  
  static size_t	zone_size(malloc_zone_t *zone, void *ptr);
  static void	*zone_malloc(malloc_zone_t *zone, size_t size);
  static void	*zone_calloc(malloc_zone_t *zone, size_t num, size_t size);
  static void	*zone_valloc(malloc_zone_t *zone, size_t size);
  static void	zone_free(malloc_zone_t *zone, void *ptr);
  static void	*zone_realloc(malloc_zone_t *zone, void *ptr, size_t size);
  #if (JEMALLOC_ZONE_VERSION >= 5)
  static void	*zone_memalign(malloc_zone_t *zone, size_t alignment,
  #endif
  #if (JEMALLOC_ZONE_VERSION >= 6)
      size_t size);
  static void	zone_free_definite_size(malloc_zone_t *zone, void *ptr,
      size_t size);
  #endif
  static void	*zone_destroy(malloc_zone_t *zone);
  static size_t	zone_good_size(malloc_zone_t *zone, size_t size);
  static void	zone_force_lock(malloc_zone_t *zone);
  static void	zone_force_unlock(malloc_zone_t *zone);
  
  /******************************************************************************/
  /*
   * Functions.
   */
  
  static size_t
  zone_size(malloc_zone_t *zone, void *ptr)
  {
  
  	/*
  	 * There appear to be places within Darwin (such as setenv(3)) that
  	 * cause calls to this function with pointers that *no* zone owns.  If
  	 * we knew that all pointers were owned by *some* zone, we could split
  	 * our zone into two parts, and use one as the default allocator and
  	 * the other as the default deallocator/reallocator.  Since that will
  	 * not work in practice, we must check all pointers to assure that they
  	 * reside within a mapped chunk before determining size.
  	 */
  	return (ivsalloc(ptr, config_prof));
  }
  
  static void *
  zone_malloc(malloc_zone_t *zone, size_t size)
  {
  
  	return (je_malloc(size));
  }
  
  static void *
  zone_calloc(malloc_zone_t *zone, size_t num, size_t size)
  {
  
  	return (je_calloc(num, size));
  }
  
  static void *
  zone_valloc(malloc_zone_t *zone, size_t size)
  {
  	void *ret = NULL; /* Assignment avoids useless compiler warning. */
  
  	je_posix_memalign(&ret, PAGE, size);
  
  	return (ret);
  }
  
  static void
  zone_free(malloc_zone_t *zone, void *ptr)
  {
  
  	if (ivsalloc(ptr, config_prof) != 0) {
  		je_free(ptr);
  		return;
  	}
  
  	free(ptr);
  }
  
  static void *
  zone_realloc(malloc_zone_t *zone, void *ptr, size_t size)
  {
  
  	if (ivsalloc(ptr, config_prof) != 0)
  		return (je_realloc(ptr, size));
  
  	return (realloc(ptr, size));
  }
  
  #if (JEMALLOC_ZONE_VERSION >= 5)
  static void *
  zone_memalign(malloc_zone_t *zone, size_t alignment, size_t size)
  {
  	void *ret = NULL; /* Assignment avoids useless compiler warning. */
  
  	je_posix_memalign(&ret, alignment, size);
  
  	return (ret);
  }
  #endif
  
  #if (JEMALLOC_ZONE_VERSION >= 6)
  static void
  zone_free_definite_size(malloc_zone_t *zone, void *ptr, size_t size)
  {
  
  	if (ivsalloc(ptr, config_prof) != 0) {
  		assert(ivsalloc(ptr, config_prof) == size);
  		je_free(ptr);
  		return;
  	}
  
  	free(ptr);
  }
  #endif
  
  static void *
  zone_destroy(malloc_zone_t *zone)
  {
  
  	/* This function should never be called. */
  	assert(false);
  	return (NULL);
  }
  
  static size_t
  zone_good_size(malloc_zone_t *zone, size_t size)
  {
  
  	if (size == 0)
  		size = 1;
  	return (s2u(size));
  }
  
  static void
  zone_force_lock(malloc_zone_t *zone)
  {
  
  	if (isthreaded)
  		jemalloc_prefork();
  }
  
  static void
  zone_force_unlock(malloc_zone_t *zone)
  {
  
  	if (isthreaded)
  		jemalloc_postfork_parent();
  }
  
  JEMALLOC_ATTR(constructor)
  void
  register_zone(void)
  {
  
  	zone.size = (void *)zone_size;
  	zone.malloc = (void *)zone_malloc;
  	zone.calloc = (void *)zone_calloc;
  	zone.valloc = (void *)zone_valloc;
  	zone.free = (void *)zone_free;
  	zone.realloc = (void *)zone_realloc;
  	zone.destroy = (void *)zone_destroy;
  	zone.zone_name = "jemalloc_zone";
  	zone.batch_malloc = NULL;
  	zone.batch_free = NULL;
  	zone.introspect = &zone_introspect;
  	zone.version = JEMALLOC_ZONE_VERSION;
  #if (JEMALLOC_ZONE_VERSION >= 5)
  	zone.memalign = zone_memalign;
  #endif
  #if (JEMALLOC_ZONE_VERSION >= 6)
  	zone.free_definite_size = zone_free_definite_size;
  #endif
  #if (JEMALLOC_ZONE_VERSION >= 8)
  	zone.pressure_relief = NULL;
  #endif
  
  	zone_introspect.enumerator = NULL;
  	zone_introspect.good_size = (void *)zone_good_size;
  	zone_introspect.check = NULL;
  	zone_introspect.print = NULL;
  	zone_introspect.log = NULL;
  	zone_introspect.force_lock = (void *)zone_force_lock;
  	zone_introspect.force_unlock = (void *)zone_force_unlock;
  	zone_introspect.statistics = NULL;
  #if (JEMALLOC_ZONE_VERSION >= 6)
  	zone_introspect.zone_locked = NULL;
  #endif
  #if (JEMALLOC_ZONE_VERSION >= 7)
  	zone_introspect.enable_discharge_checking = NULL;
  	zone_introspect.disable_discharge_checking = NULL;
  	zone_introspect.discharge = NULL;
  #ifdef __BLOCKS__
  	zone_introspect.enumerate_discharged_pointers = NULL;
  #else
  	zone_introspect.enumerate_unavailable_without_blocks = NULL;
  #endif
  #endif
  
  	/*
  	 * The default purgeable zone is created lazily by OSX's libc.  It uses
  	 * the default zone when it is created for "small" allocations
  	 * (< 15 KiB), but assumes the default zone is a scalable_zone.  This
  	 * obviously fails when the default zone is the jemalloc zone, so
  	 * malloc_default_purgeable_zone is called beforehand so that the
  	 * default purgeable zone is created when the default zone is still
  	 * a scalable_zone.  As purgeable zones only exist on >= 10.6, we need
  	 * to check for the existence of malloc_default_purgeable_zone() at
  	 * run time.
  	 */
  	if (malloc_default_purgeable_zone != NULL)
  		malloc_default_purgeable_zone();
  
  	/* Register the custom zone.  At this point it won't be the default. */
  	malloc_zone_register(&zone);
  
  	/*
  	 * Unregister and reregister the default zone.  On OSX >= 10.6,
  	 * unregistering takes the last registered zone and places it at the
  	 * location of the specified zone.  Unregistering the default zone thus
  	 * makes the last registered one the default.  On OSX < 10.6,
  	 * unregistering shifts all registered zones.  The first registered zone
  	 * then becomes the default.
  	 */
  	do {
  		malloc_zone_t *default_zone = malloc_default_zone();
  		malloc_zone_unregister(default_zone);
  		malloc_zone_register(default_zone);
  	} while (malloc_default_zone() != &zone);
  }
  