[svn-r18072] Description:

	Bring r18071 from metadata journaling merge branch:

	Refactor local heap routines with changes from metadata journaling
branch, along with other misc. changes as the changes on the metadata journaling
branch are being converged with the current state of the trunk.

Tested on:
        FreeBSD/32 6.3 (duty) in debug mode
        FreeBSD/64 6.3 (liberty) w/C++ & FORTRAN, in debug mode
        Linux/32 2.6 (jam) w/PGI compilers, w/default API=1.8.x,
                w/C++ & FORTRAN, w/threadsafe, in debug mode
        Linux/64-amd64 2.6 (amani) w/Intel compilers, w/default API=1.6.x,
                w/C++ & FORTRAN, in production mode
        Solaris/32 2.10 (linew) w/deprecated symbols disabled, w/C++ & FORTRAN,
                w/szip filter, in production mode
        Linux/64-ia64 2.6 (cobalt) w/Intel compilers, w/C++ & FORTRAN,
                in production mode
        Linux/64-ia64 2.4 (tg-login3) w/parallel, w/FORTRAN, in debug mode
        Linux/64-amd64 2.6 (abe) w/parallel, w/FORTRAN, in production mode
        Mac OS X/32 10.6.2 (amazon) in debug mode
        Mac OS X/32 10.6.2 (amazon) w/C++ & FORTRAN, w/threadsafe,
                in production mode

1 files changed, 581 insertions, 229 deletions

diff --git a/src/H5HLcache.c b/src/H5HLcache.c
index 8f617f7..a26477a 100644
--- a/src/H5HLcache.c
+++ b/src/H5HLcache.c
@@ -38,6 +38,7 @@
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5HLpkg.h"		/* Local Heaps				*/
 #include "H5MFprivate.h"	/* File memory management		*/
+#include "H5WBprivate.h"        /* Wrapped Buffers                      */
 
 
 /****************/
@@ -45,7 +46,12 @@
 /****************/
 
 #define H5HL_VERSION	0               /* Local heap collection version    */
-#define H5HL_FREE_NULL	1		/* End of free list on disk	    */
+
+/* Set the local heap size to speculatively read in */
+/* (needs to be more than the local heap prefix size to work at all and
+ *      should be larger than the default local heap size to save the
+ *      extra I/O operations) */
+#define H5HL_SPEC_READ_SIZE 512
 
 
 /******************/
@@ -62,14 +68,21 @@
 /* Local Prototypes */
 /********************/
 
-/* Local encode/decode routines */
-static herr_t H5HL_serialize(H5F_t *f, H5HL_t *heap, uint8_t *buf);
-
 /* Metadata cache callbacks */
-static H5HL_t *H5HL_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void *udata1,
-			 void *udata2);
-static herr_t H5HL_flush(H5F_t *f, hid_t dxpl_id, hbool_t dest, haddr_t addr, H5HL_t *heap, unsigned UNUSED * flags_ptr);
-static herr_t H5HL_clear(H5F_t *f, H5HL_t *heap, hbool_t destroy);
+static void *H5HL_prefix_load(H5F_t *f, hid_t dxpl_id, haddr_t addr,
+    const void *udata1, void *udata2);
+static herr_t H5HL_prefix_flush(H5F_t *f, hid_t dxpl_id, hbool_t dest, haddr_t addr,
+    void *thing, unsigned *flags_ptr);
+static herr_t H5HL_prefix_dest(H5F_t *f, void *thing);
+static herr_t H5HL_prefix_clear(H5F_t *f, void *thing, hbool_t destroy);
+static herr_t H5HL_prefix_size(const H5F_t *f, const void *thing, size_t *size_ptr);
+static void *H5HL_datablock_load(H5F_t *f, hid_t dxpl_id, haddr_t addr,
+    const void *udata1, void *udata2);
+static herr_t H5HL_datablock_flush(H5F_t *f, hid_t dxpl_id, hbool_t dest, haddr_t addr,
+    void *thing, unsigned *flags_ptr);
+static herr_t H5HL_datablock_dest(H5F_t *f, void *thing);
+static herr_t H5HL_datablock_clear(H5F_t *f, void *thing, hbool_t destroy);
+static herr_t H5HL_datablock_size(const H5F_t *f, const void *thing, size_t *size_ptr);
 
 
 /*********************/
@@ -77,14 +90,24 @@ static herr_t H5HL_clear(H5F_t *f, H5HL_t *heap, hbool_t destroy);
 /*********************/
 
 /* H5HL inherits cache-like properties from H5AC */
-const H5AC_class_t H5AC_LHEAP[1] = {{
-    H5AC_LHEAP_ID,
-    (H5AC_load_func_t)H5HL_load,
-    (H5AC_flush_func_t)H5HL_flush,
-    (H5AC_dest_func_t)H5HL_dest,
-    (H5AC_clear_func_t)H5HL_clear,
-    (H5AC_notify_func_t)NULL,
-    (H5AC_size_func_t)H5HL_size,
+const H5AC_class_t H5AC_LHEAP_PRFX[1] = {{
+    H5AC_LHEAP_PRFX_ID,
+    H5HL_prefix_load,
+    H5HL_prefix_flush,
+    H5HL_prefix_dest,
+    H5HL_prefix_clear,
+    NULL,
+    H5HL_prefix_size,
+}};
+
+const H5AC_class_t H5AC_LHEAP_DBLK[1] = {{
+    H5AC_LHEAP_DBLK_ID,
+    H5HL_datablock_load,
+    H5HL_datablock_flush,
+    H5HL_datablock_dest,
+    H5HL_datablock_clear,
+    NULL,
+    H5HL_datablock_size,
 }};
 
 
@@ -100,72 +123,117 @@ const H5AC_class_t H5AC_LHEAP[1] = {{
 
 
 /*-------------------------------------------------------------------------
- * Function:    H5HL_serialize
+ * Function:	H5HL_fl_deserialize
  *
- * Purpose:     Serialize the heap. This function will eliminate free
- *              blocks at the tail of the heap and also split the block
- *              if it needs to be split for the file. This is so that we
- *              can serialize it correctly.
+ * Purpose:	Deserialize the free list for a heap data block
  *
  * Return:      Non-negative on success/Negative on failure
  *
- * Programmer:  Bill Wendling
- *              wendling@ncsa.uiuc.edu
- *              Sept. 16, 2003
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Oct 12 2008
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5HL_serialize(H5F_t *f, H5HL_t *heap, uint8_t *buf)
+H5HL_fl_deserialize(H5HL_t *heap, hsize_t free_block)
 {
-    H5HL_free_t	   *fl;
-    uint8_t        *p;
-    herr_t          ret_value = SUCCEED;
+    H5HL_free_t *fl, *tail = NULL;      /* Heap free block nodes */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_fl_deserialize)
 
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HL_serialize)
+    /* check arguments */
+    HDassert(heap);
 
-    /* check args */
-    assert(buf);
-    assert(heap);
+    /* Build free list */
+    while(H5HL_FREE_NULL != free_block) {
+        const uint8_t *p;               /* Pointer into image buffer */
 
-    /* serialize the header */
-    p = buf;
-    fl = heap->freelist;
-    HDmemcpy(p, H5HL_MAGIC, (size_t)H5_SIZEOF_MAGIC);
-    p += H5_SIZEOF_MAGIC;
-    *p++ = H5HL_VERSION;
-    *p++ = 0;	/*reserved*/
-    *p++ = 0;	/*reserved*/
-    *p++ = 0;	/*reserved*/
-    H5F_ENCODE_LENGTH(f, p, heap->heap_alloc);
-    H5F_ENCODE_LENGTH(f, p, fl ? fl->offset : H5HL_FREE_NULL);
-    H5F_addr_encode(f, &p, heap->addr);
-
-    /* serialize the free list */
-    for (; fl; fl = fl->next) {
-        assert (fl->offset == H5HL_ALIGN (fl->offset));
-        p = heap->chunk + H5HL_SIZEOF_HDR(f) + fl->offset;
-
-        if (fl->next) {
-            H5F_ENCODE_LENGTH(f, p, fl->next->offset);
-        } else {
-            H5F_ENCODE_LENGTH(f, p, H5HL_FREE_NULL);
-        }
-
-        H5F_ENCODE_LENGTH(f, p, fl->size);
-    }
+        /* Sanity check */
+        if(free_block >= heap->dblk_size)
+            HGOTO_ERROR(H5E_HEAP, H5E_BADRANGE, FAIL, "bad heap free list")
+
+        /* Allocate & initialize free list node */
+        if(NULL == (fl = H5FL_MALLOC(H5HL_free_t)))
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, FAIL, "memory allocation failed")
+        fl->offset = (size_t)free_block;
+        fl->prev = tail;
+        fl->next = NULL;
 
+        /* Insert node into list */
+        if(tail)
+            tail->next = fl;
+        tail = fl;
+        if(!heap->freelist)
+            heap->freelist = fl;
+
+        /* Decode offset of next free block */
+        p = heap->dblk_image + free_block;
+        H5F_DECODE_LENGTH_LEN(p, free_block, heap->sizeof_size);
+        if(free_block == 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, FAIL, "free block size is zero?")
+
+        /* Decode length of this free block */
+        H5F_DECODE_LENGTH_LEN(p, fl->size, heap->sizeof_size);
+        if(fl->offset + fl->size > heap->dblk_size)
+            HGOTO_ERROR(H5E_HEAP, H5E_BADRANGE, FAIL, "bad heap free list")
+    } /* end while */
+
+done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5HL_serialize() */
+} /* end H5HL_fl_deserialize() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5HL_load
+ * Function:	H5HL_fl_serialize
  *
- * Purpose:	Loads a heap from disk.
+ * Purpose:	Serialize the free list for a heap data block
  *
- * Return:	Success:	Ptr to a local heap memory data structure.
+ * Return:	Success:	SUCCESS
+ *		Failure:	FAIL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Oct 12 2008
  *
+ *-------------------------------------------------------------------------
+ */
+static void
+H5HL_fl_serialize(const H5HL_t *heap)
+{
+    H5HL_free_t	*fl;                    /* Pointer to heap free list node */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HL_fl_serialize)
+
+    /* check arguments */
+    HDassert(heap);
+
+    /* Serialize the free list into the heap data's image */
+    for(fl = heap->freelist; fl; fl = fl->next) {
+        uint8_t     *p;                     /* Pointer into raw data buffer */
+
+        HDassert(fl->offset == H5HL_ALIGN(fl->offset));
+        p = heap->dblk_image + fl->offset;
+
+        if(fl->next)
+            H5F_ENCODE_LENGTH_LEN(p, fl->next->offset, heap->sizeof_size)
+        else
+            H5F_ENCODE_LENGTH_LEN(p, H5HL_FREE_NULL, heap->sizeof_size)
+
+        H5F_ENCODE_LENGTH_LEN(p, fl->size, heap->sizeof_size)
+    } /* end for */
+
+    FUNC_LEAVE_NOAPI_VOID
+} /* end H5HL_fl_serialize() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HL_prefix_load
+ *
+ * Purpose:	Loads a local heap prefix from disk.
+ *
+ * Return:	Success:	Ptr to a local heap memory data structure.
  *		Failure:	NULL
  *
  * Programmer:	Robb Matzke
@@ -174,38 +242,47 @@ H5HL_serialize(H5F_t *f, H5HL_t *heap, uint8_t *buf)
  *
  *-------------------------------------------------------------------------
  */
-static H5HL_t *
-H5HL_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * udata1,
-	  void UNUSED * udata2)
+static void *
+H5HL_prefix_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void *udata1,
+    void *_udata)
 {
-    uint8_t		hdr[52];
-    size_t              sizeof_hdr;     /* Cache H5HL header size for file */
-    const uint8_t	*p = NULL;
-    H5HL_t		*heap = NULL;
-    H5HL_free_t		*fl = NULL, *tail = NULL;
-    size_t		free_block = H5HL_FREE_NULL;
-    H5HL_t		*ret_value;
+    H5HL_t              *heap = NULL; /* Local heap */
+    H5HL_prfx_t         *prfx = NULL; /* Heap prefix deserialized */
+    H5HL_cache_prfx_ud_t *udata = (H5HL_cache_prfx_ud_t *)_udata; /* User data for protecting local heap prefix */
+    uint8_t		buf[H5HL_SPEC_READ_SIZE];   /* Buffer for decoding */
+    size_t	        spec_read_size; /* Size of buffer to speculatively read in */
+    const uint8_t	*p;         /* Pointer into decoding buffer */
+    haddr_t             eoa;        /* Relative end of file address */
+    void                *ret_value; /* Return value */
 
-    FUNC_ENTER_NOAPI(H5HL_load, NULL)
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_prefix_load)
 
     /* check arguments */
     HDassert(f);
     HDassert(H5F_addr_defined(addr));
     HDassert(!udata1);
-    HDassert(!udata2);
-
-    /* Cache this for later */
-    sizeof_hdr = H5HL_SIZEOF_HDR(f);
-    HDassert(sizeof_hdr <= sizeof(hdr));
-
-    /* Get the local heap's header */
-    if(H5F_block_read(f, H5FD_MEM_LHEAP, addr, sizeof_hdr, dxpl_id, hdr) < 0)
-	HGOTO_ERROR(H5E_HEAP, H5E_READERROR, NULL, "unable to read heap header")
-    p = hdr;
+    HDassert(udata);
+    HDassert(udata->sizeof_size > 0);
+    HDassert(udata->sizeof_addr > 0);
+    HDassert(udata->sizeof_prfx > 0);
+    HDassert(udata->sizeof_prfx <= sizeof(buf));
+
+    /* Make certain we don't speculatively read off the end of the file */
+    if(HADDR_UNDEF == (eoa = H5F_get_eoa(f, H5FD_MEM_LHEAP)))
+        HGOTO_ERROR(H5E_HEAP, H5E_CANTGET, NULL, "unable to determine file size")
+
+    /* Compute the size of the speculative local heap prefix buffer */
+    H5_ASSIGN_OVERFLOW(spec_read_size, MIN(eoa - addr, H5HL_SPEC_READ_SIZE), /* From: */ hsize_t, /* To: */ size_t);
+    HDassert(spec_read_size >= udata->sizeof_prfx);
+
+    /* Attempt to speculatively read both local heap prefix and heap data */
+    if(H5F_block_read(f, H5FD_MEM_LHEAP, addr, spec_read_size, dxpl_id, buf) < 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_READERROR, NULL, "unable to read local heap prefix")
+    p = buf;
 
     /* Check magic number */
-    if(HDmemcmp(hdr, H5HL_MAGIC, (size_t)H5_SIZEOF_MAGIC))
-	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, NULL, "bad heap signature")
+    if(HDmemcmp(p, H5HL_MAGIC, (size_t)H5_SIZEOF_MAGIC))
+	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, NULL, "bad local heap signature")
     p += H5_SIZEOF_MAGIC;
 
     /* Version */
@@ -216,65 +293,84 @@ H5HL_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * udata1,
     p += 3;
 
     /* Allocate space in memory for the heap */
-    if(NULL == (heap = H5FL_CALLOC(H5HL_t)))
-	HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "memory allocation failed")
+    if(NULL == (heap = H5HL_new(udata->sizeof_size, udata->sizeof_addr, udata->sizeof_prfx)))
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "can't allocate local heap structure")
 
-    /* heap data size */
-    H5F_DECODE_LENGTH(f, p, heap->heap_alloc);
+    /* Allocate the heap prefix */
+    if(NULL == (prfx = H5HL_prfx_new(heap)))
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "can't allocate local heap prefix")
 
-    /* free list head */
-    H5F_DECODE_LENGTH(f, p, free_block);
-    if(free_block != H5HL_FREE_NULL && free_block >= heap->heap_alloc)
-	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, NULL, "bad heap free list")
+    /* Store the prefix's address & length */
+    heap->prfx_addr = addr;
+    heap->prfx_size = udata->sizeof_prfx;
 
-    /* data */
-    H5F_addr_decode(f, &p, &(heap->addr));
-    if(NULL == (heap->chunk = H5FL_BLK_CALLOC(lheap_chunk, (sizeof_hdr + heap->heap_alloc))))
-	HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "memory allocation failed")
-    if(heap->heap_alloc &&
-            H5F_block_read(f, H5FD_MEM_LHEAP, heap->addr, heap->heap_alloc, dxpl_id, heap->chunk + sizeof_hdr) < 0)
-	HGOTO_ERROR(H5E_HEAP, H5E_READERROR, NULL, "unable to read heap data")
+    /* Heap data size */
+    H5F_DECODE_LENGTH_LEN(p, heap->dblk_size, udata->sizeof_size);
 
-    /* Build free list */
-    while(H5HL_FREE_NULL != free_block) {
-	if(free_block >= heap->heap_alloc)
-	    HGOTO_ERROR(H5E_HEAP, H5E_BADRANGE, NULL, "bad heap free list")
-	if(NULL == (fl = H5FL_MALLOC(H5HL_free_t)))
-	    HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "memory allocation failed")
-	fl->offset = free_block;
-	fl->prev = tail;
-	fl->next = NULL;
-	if(tail)
-            tail->next = fl;
-	tail = fl;
-	if(!heap->freelist)
-            heap->freelist = fl;
-
-	p = heap->chunk + sizeof_hdr + free_block;
+    /* Free list head */
+    H5F_DECODE_LENGTH_LEN(p, udata->free_block, udata->sizeof_size);
+    if(udata->free_block != H5HL_FREE_NULL && udata->free_block >= heap->dblk_size)
+	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, NULL, "bad heap free list")
 
-	H5F_DECODE_LENGTH(f, p, free_block);
-	if(free_block == 0)
-	    HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, NULL, "free block size is zero?")
+    /* Heap data address */
+    H5F_addr_decode_len(udata->sizeof_addr, &p, &(heap->dblk_addr));
+
+    /* Check if heap block exists */
+    if(heap->dblk_size) {
+        /* Check if heap data block is contiguous with header */
+        if(H5F_addr_eq((heap->prfx_addr + heap->prfx_size), heap->dblk_addr)) {
+            /* Note that the heap should be a single object in the cache */
+            heap->single_cache_obj = TRUE;
+
+            /* Allocate space for the heap data image */
+            if(NULL == (heap->dblk_image = H5FL_BLK_MALLOC(lheap_chunk, heap->dblk_size)))
+                HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "memory allocation failed")
+
+            /* Check if the current buffer from the speculative read already has the heap data */
+            if(spec_read_size >= (heap->prfx_size + heap->dblk_size)) {
+                /* Copy the heap data from the speculative read buffer */
+                HDmemcpy(heap->dblk_image, p, heap->dblk_size);
+            } /* end if */
+            else {
+                /* Read the local heap data block directly into buffer */
+                if(H5F_block_read(f, H5FD_MEM_LHEAP, heap->dblk_addr, heap->dblk_size, dxpl_id, heap->dblk_image) < 0)
+                    HGOTO_ERROR(H5E_HEAP, H5E_READERROR, NULL, "unable to read heap data")
+            } /* end else */
+
+            /* Build free list */
+            if(H5HL_fl_deserialize(heap, udata->free_block) < 0)
+                HGOTO_ERROR(H5E_HEAP, H5E_CANTINIT, NULL, "can't initialize free list")
+        } /* end if */
+        else
+            /* Note that the heap should _NOT_ be a single object in the cache */
+            heap->single_cache_obj = FALSE;
+    } /* end if */
 
-	H5F_DECODE_LENGTH(f, p, fl->size);
-	if(fl->offset + fl->size > heap->heap_alloc)
-	    HGOTO_ERROR(H5E_HEAP, H5E_BADRANGE, NULL, "bad heap free list")
-    } /* end while */
+    /* Set flag to indicate prefix from loaded from file */
+    udata->loaded = TRUE;
 
     /* Set return value */
-    ret_value = heap;
+    ret_value = prfx;
 
 done:
-    if(!ret_value && heap)
-        if(H5HL_dest(f,heap) < 0)
-	    HDONE_ERROR(H5E_HEAP, H5E_CANTFREE, NULL, "unable to destroy local heap collection")
+    /* Release the [possibly partially initialized] local heap on errors */
+    if(!ret_value) {
+        if(prfx) {
+            if(H5HL_prfx_dest(prfx) < 0)
+                HDONE_ERROR(H5E_HEAP, H5E_CANTRELEASE, NULL, "unable to destroy local heap prefix")
+        } /* end if */
+        else {
+            if(heap && H5HL_dest(heap) < 0)
+                HDONE_ERROR(H5E_HEAP, H5E_CANTRELEASE, NULL, "unable to destroy local heap")
+        } /* end else */
+    } /* end if */
 
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5HL_load() */
+} /* end H5HL_prefix_load() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5HL_flush
+ * Function:	H5HL_prefix_flush
  *
  * Purpose:	Flushes a heap from memory to disk if it's dirty.  Optionally
  *		deletes the heap from memory.
@@ -288,58 +384,336 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5HL_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5HL_t *heap, unsigned UNUSED * flags_ptr)
+H5HL_prefix_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr,
+    void *thing, unsigned UNUSED *flags_ptr)
 {
-    herr_t  ret_value = SUCCEED;    /* Return value */
+    H5HL_prfx_t *prfx = (H5HL_prfx_t *)thing;   /* Local heap prefix to flush */
+    H5WB_t *wb = NULL;                  /* Wrapped buffer for heap data */
+    uint8_t heap_buf[H5HL_SPEC_READ_SIZE]; /* Buffer for heap */
+    herr_t ret_value = SUCCEED;         /* Return value */
 
-    FUNC_ENTER_NOAPI(H5HL_flush, FAIL)
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_prefix_flush)
 
     /* check arguments */
     HDassert(f);
     HDassert(H5F_addr_defined(addr));
-    HDassert(heap);
+    HDassert(prfx);
+
+    if(prfx->cache_info.is_dirty) {
+        H5HL_t *heap = prfx->heap; /* Pointer to the local heap */
+        H5HL_free_t *fl = heap->freelist; /* Pointer to heap's free list */
+        uint8_t *buf;           /* Pointer to heap buffer */
+        size_t buf_size;        /* Size of buffer for encoding & writing heap info */
+        uint8_t *p;             /* Pointer into raw data buffer */
+
+        /* Wrap the local buffer for serialized heap info */
+        if(NULL == (wb = H5WB_wrap(heap_buf, sizeof(heap_buf))))
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTINIT, FAIL, "can't wrap buffer")
+
+        /* Compute the size of the buffer to encode & write */
+        buf_size = heap->prfx_size;
+        if(heap->single_cache_obj)
+            buf_size += heap->dblk_size;
+
+        /* Get a pointer to a buffer that's large enough for serialized heap */
+        if(NULL == (buf = (uint8_t *)H5WB_actual(wb, buf_size)))
+            HGOTO_ERROR(H5E_HEAP, H5E_NOSPACE, FAIL, "can't get actual buffer")
+
+        /* Serialize the heap prefix */
+        p = buf;
+        HDmemcpy(p, H5HL_MAGIC, (size_t)H5_SIZEOF_MAGIC);
+        p += H5_SIZEOF_MAGIC;
+        *p++ = H5HL_VERSION;
+        *p++ = 0;	/*reserved*/
+        *p++ = 0;	/*reserved*/
+        *p++ = 0;	/*reserved*/
+        H5F_ENCODE_LENGTH_LEN(p, heap->dblk_size, heap->sizeof_size);
+        H5F_ENCODE_LENGTH_LEN(p, fl ? fl->offset : H5HL_FREE_NULL, heap->sizeof_size);
+        H5F_addr_encode_len(heap->sizeof_addr, &p, heap->dblk_addr);
+
+        /* Check if the local heap is a single object in cache */
+        if(heap->single_cache_obj) {
+            /* Serialize the free list into the heap data's image */
+            H5HL_fl_serialize(heap);
+
+            /* Copy the heap data block into the cache image */
+            HDmemcpy(p, heap->dblk_image, heap->dblk_size);
+        } /* end if */
 
-    if(heap->cache_info.is_dirty) {
-        haddr_t hdr_end_addr;
-        size_t  sizeof_hdr = H5HL_SIZEOF_HDR(f);    /* cache H5HL header size for file */
+        /* Write the prefix [and possibly the data block] to the file */
+        if(H5F_block_write(f, H5FD_MEM_LHEAP, addr, buf_size, dxpl_id, buf) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_WRITEERROR, FAIL, "unable to write heap header and data to file")
 
-	/* Write the header */
-        if(H5HL_serialize(f, heap, heap->chunk) < 0)
-            HGOTO_ERROR(H5E_HEAP, H5E_CANTSERIALIZE, FAIL, "unable to serialize local heap")
+	prfx->cache_info.is_dirty = FALSE;
+    } /* end if */
 
-	/* Copy buffer to disk */
-	hdr_end_addr = addr + (hsize_t)sizeof_hdr;
+    /* Should we destroy the memory version? */
+    if(destroy)
+        if(H5HL_prfx_dest(prfx) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy local heap prefix")
 
-	if(H5F_addr_eq(heap->addr, hdr_end_addr)) {
-	    /* The header and data are contiguous */
-	    if(H5F_block_write(f, H5FD_MEM_LHEAP, addr, (sizeof_hdr + heap->heap_alloc), dxpl_id, heap->chunk) < 0)
-		HGOTO_ERROR(H5E_HEAP, H5E_WRITEERROR, FAIL, "unable to write heap header and data to file")
-	} /* end if */
-        else {
-	    if(H5F_block_write(f, H5FD_MEM_LHEAP, addr, sizeof_hdr, dxpl_id, heap->chunk) < 0)
-		HGOTO_ERROR(H5E_HEAP, H5E_WRITEERROR, FAIL, "unable to write heap header to file")
+done:
+    /* Release resources */
+    if(wb && H5WB_unwrap(wb) < 0)
+        HDONE_ERROR(H5E_HEAP, H5E_CLOSEERROR, FAIL, "can't close wrapped buffer")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HL_prefix_flush() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HL_prefix_dest
+ *
+ * Purpose:	Destroys a heap prefix in memory.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Jan 15 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HL_prefix_dest(H5F_t UNUSED *f, void *thing)
+{
+    H5HL_prfx_t *prfx = (H5HL_prfx_t *)thing;   /* Local heap prefix to destroy */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_prefix_dest)
 
-	    if(H5F_block_write(f, H5FD_MEM_LHEAP, heap->addr, heap->heap_alloc, dxpl_id, heap->chunk + sizeof_hdr) < 0)
-		HGOTO_ERROR(H5E_HEAP, H5E_WRITEERROR, FAIL, "unable to write heap data to file")
-	} /* end else */
+    /* check arguments */
+    HDassert(prfx);
+    HDassert(prfx->heap);
+    HDassert(H5F_addr_eq(prfx->cache_info.addr, prfx->heap->prfx_addr));
+
+    /* Verify that entry is clean */
+    HDassert(prfx->cache_info.is_dirty == FALSE);
+
+    /* If we're going to free the space on disk, the address must be valid */
+    HDassert(!prfx->cache_info.free_file_space_on_destroy || H5F_addr_defined(prfx->cache_info.addr));
 
-	heap->cache_info.is_dirty = FALSE;
+    /* Check for freeing file space for local heap prefix */
+    if(prfx->cache_info.free_file_space_on_destroy) {
+        hsize_t free_size;       /* Size of region to free in file */
+
+        /* Compute size to free for later */
+        free_size = prfx->heap->prfx_size;
+        if(prfx->heap->single_cache_obj)
+            free_size += prfx->heap->dblk_size;
+
+        /* Free the local heap prefix [and possible the data block] on disk */
+        /* (XXX: Nasty usage of internal DXPL value! -QAK) */
+        if(H5MF_xfree(f, H5FD_MEM_LHEAP, H5AC_dxpl_id, prfx->cache_info.addr, free_size) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to free local heap prefix")
+    } /* end if */
+
+    /* Destroy local heap prefix */
+    if(H5HL_prfx_dest(prfx) < 0)
+        HGOTO_ERROR(H5E_HEAP, H5E_CANTRELEASE, FAIL, "can't destroy local heap prefix")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HL_prefix_dest() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HL_prefix_clear
+ *
+ * Purpose:	Mark a local heap prefix in memory as non-dirty.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Mar 20 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HL_prefix_clear(H5F_t UNUSED *f, void *thing, hbool_t destroy)
+{
+    H5HL_prfx_t *prfx = (H5HL_prfx_t *)thing;   /* The local heap prefix to operate on */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_prefix_clear)
+
+    /* check arguments */
+    HDassert(prfx);
+
+    /* Mark heap prefix as clean */
+    prfx->cache_info.is_dirty = FALSE;
+
+    if(destroy)
+        if(H5HL_prfx_dest(prfx) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy local heap prefix")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HL_prefix_clear() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HL_prefix_size
+ *
+ * Purpose:	Compute the size in bytes of the heap prefix on disk,
+ *              and return it in *len_ptr.  On failure, the value of *len_ptr
+ *              is undefined.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	John Mainzer
+ *		5/13/04
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HL_prefix_size(const H5F_t UNUSED *f, const void *thing, size_t *size_ptr)
+{
+    const H5HL_prfx_t *prfx = (const H5HL_prfx_t *)thing;   /* Pointer to local heap prefix to query */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HL_prefix_size)
+
+    /* check arguments */
+    HDassert(prfx);
+    HDassert(prfx->heap);
+    HDassert(size_ptr);
+
+    /* Calculate size of prefix in cache */
+    *size_ptr = prfx->heap->prfx_size;
+
+    /* If the heap is stored as a single object, add in the data block size also */
+    if(prfx->heap->single_cache_obj)
+        *size_ptr += prfx->heap->dblk_size;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* H5HL_prefix_size() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HL_datablock_load
+ *
+ * Purpose:	Loads a local heap data block from disk.
+ *
+ * Return:	Success:	Ptr to a local heap data block memory data structure.
+ *		Failure:	NULL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Jan  5 2010
+ *
+ *-------------------------------------------------------------------------
+ */
+static void *
+H5HL_datablock_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void *udata1,
+    void *_udata)
+{
+    H5HL_dblk_t         *dblk = NULL; /* Heap data block deserialized */
+    H5HL_cache_dblk_ud_t *udata = (H5HL_cache_dblk_ud_t *)_udata; /* User data for protecting local heap data block */
+    void                *ret_value; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_datablock_load)
+
+    /* check arguments */
+    HDassert(f);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(!udata1);
+    HDassert(udata);
+    HDassert(udata->heap);
+    HDassert(!udata->heap->single_cache_obj);
+
+    /* Allocate space in memory for the heap data block */
+    if(NULL == (dblk = H5HL_dblk_new(udata->heap)))
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "memory allocation failed")
+
+    /* Check for heap still retaining image */
+    if(NULL == udata->heap->dblk_image) {
+        /* Allocate space for the heap data image */
+        if(NULL == (udata->heap->dblk_image = H5FL_BLK_MALLOC(lheap_chunk, udata->heap->dblk_size)))
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, NULL, "can't allocate data block image buffer")
+
+        /* Read local heap data block */
+        if(H5F_block_read(f, H5FD_MEM_LHEAP, udata->heap->dblk_addr, udata->heap->dblk_size, dxpl_id, udata->heap->dblk_image) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_READERROR, NULL, "unable to read local heap data block")
+
+        /* Build free list */
+        if(H5HL_fl_deserialize(udata->heap, udata->free_block) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTINIT, NULL, "can't initialize free list")
+    } /* end if */
+
+    /* Set flag to indicate data block from loaded from file */
+    udata->loaded = TRUE;
+
+    /* Set return value */
+    ret_value = dblk;
+
+done:
+    /* Release the [possibly partially initialized] local heap on errors */
+    if(!ret_value && dblk)
+        if(H5HL_dblk_dest(f, dblk) < 0)
+	    HDONE_ERROR(H5E_HEAP, H5E_CANTRELEASE, NULL, "unable to destroy local heap data block")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HL_datablock_load() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HL_datablock_flush
+ *
+ * Purpose:	Flushes a heap's data block from memory to disk if it's dirty.
+ *              Optionally deletes the heap data block from memory.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Robb Matzke
+ *		matzke@llnl.gov
+ *		Jul 17 1997
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HL_datablock_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr,
+    void *_thing, unsigned UNUSED * flags_ptr)
+{
+    H5HL_dblk_t *dblk = (H5HL_dblk_t *)_thing; /* Pointer to the local heap data block */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_datablock_flush)
+
+    /* check arguments */
+    HDassert(f);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(dblk);
+    HDassert(dblk->heap);
+    HDassert(!dblk->heap->single_cache_obj);
+
+    if(dblk->cache_info.is_dirty) {
+        H5HL_t *heap = dblk->heap;      /* Pointer to the local heap */
+
+        /* Serialize the free list into the heap data's image */
+        H5HL_fl_serialize(heap);
+
+        /* Write the data block to the file */
+        if(H5F_block_write(f, H5FD_MEM_LHEAP, heap->dblk_addr, heap->dblk_size, dxpl_id, heap->dblk_image) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_WRITEERROR, FAIL, "unable to write heap data block to file")
+
+	dblk->cache_info.is_dirty = FALSE;
     } /* end if */
 
     /* Should we destroy the memory version? */
     if(destroy)
-        if(H5HL_dest(f, heap) < 0)
-	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy local heap collection")
+        if(H5HL_dblk_dest(f, dblk) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy local heap data block")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5HL_flush() */
+} /* end H5HL_datablock_flush() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5HL_dest
+ * Function:	H5HL_datablock_dest
  *
- * Purpose:	Destroys a heap in memory.
+ * Purpose:	Destroys a local heap data block in memory.
  *
  * Return:	Non-negative on success/Negative on failure
  *
@@ -349,75 +723,48 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-herr_t
-H5HL_dest(H5F_t *f, H5HL_t *heap)
+static herr_t
+H5HL_datablock_dest(H5F_t *f, void *_thing)
 {
-    H5HL_free_t	*fl;                    /* Heap object free list */
+    H5HL_dblk_t *dblk = (H5HL_dblk_t *)_thing; /* Pointer to the local heap data block */
     herr_t ret_value = SUCCEED;         /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5HL_dest)
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_datablock_dest)
 
     /* check arguments */
-    HDassert(heap);
+    HDassert(f);
+    HDassert(dblk);
+    HDassert(dblk->heap);
+    HDassert(!dblk->heap->single_cache_obj);
+    HDassert(H5F_addr_eq(dblk->cache_info.addr, dblk->heap->dblk_addr));
 
-    /* Verify that node is clean */
-    HDassert(heap->cache_info.is_dirty == FALSE);
+    /* Verify that entry is clean */
+    HDassert(dblk->cache_info.is_dirty == FALSE);
 
     /* If we're going to free the space on disk, the address must be valid */
-    HDassert(!heap->cache_info.free_file_space_on_destroy || H5F_addr_defined(heap->cache_info.addr));
-
-    /* Check for freeing file space for local heap */
-    if(heap->cache_info.free_file_space_on_destroy) {
-        size_t sizeof_hdr;      /* H5HL header size for file */
-        haddr_t hdr_addr;       /* Address of heap header in file */
-
-        /* Compute this for later */
-        sizeof_hdr = H5HL_SIZEOF_HDR(f);
-        hdr_addr = heap->cache_info.addr;
-
-        /* Check if the heap is contiguous on disk */
-        HDassert(!H5F_addr_overflow(hdr_addr, sizeof_hdr));
-        if(H5F_addr_eq(heap->addr, hdr_addr + sizeof_hdr)) {
-            /* Free the contiguous local heap in one call */
-            /* (XXX: Nasty usage of internal DXPL value! -QAK) */
-            H5_CHECK_OVERFLOW(sizeof_hdr + heap->heap_alloc, size_t, hsize_t);
-            if(H5MF_xfree(f, H5FD_MEM_LHEAP, H5AC_dxpl_id, hdr_addr, (hsize_t)(sizeof_hdr + heap->heap_alloc)) < 0)
-                HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to free contiguous local heap")
-        } /* end if */
-        else {
-            /* Free the local heap's header */
-            /* (XXX: Nasty usage of internal DXPL value! -QAK) */
-            H5_CHECK_OVERFLOW(sizeof_hdr, size_t, hsize_t);
-            if(H5MF_xfree(f, H5FD_MEM_LHEAP, H5AC_dxpl_id, hdr_addr, (hsize_t)sizeof_hdr) < 0)
-                HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to free local heap header")
-
-            /* Free the local heap's data */
-            /* (XXX: Nasty usage of internal DXPL value! -QAK) */
-            H5_CHECK_OVERFLOW(heap->heap_alloc, size_t, hsize_t);
-            if(H5MF_xfree(f, H5FD_MEM_LHEAP, H5AC_dxpl_id, heap->addr, (hsize_t)heap->heap_alloc) < 0)
-                HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to free local heap data")
-        } /* end else */
+    HDassert(!dblk->cache_info.free_file_space_on_destroy || H5F_addr_defined(dblk->cache_info.addr));
+
+    /* Check for freeing file space for local heap data block */
+    if(dblk->cache_info.free_file_space_on_destroy) {
+        /* Free the local heap data block on disk */
+        /* (XXX: Nasty usage of internal DXPL value! -QAK) */
+        if(H5MF_xfree(f, H5FD_MEM_LHEAP, H5AC_dxpl_id, dblk->cache_info.addr, (hsize_t)dblk->heap->dblk_size) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to free local heap data block")
     } /* end if */
 
-    /* Release resources */
-    if(heap->chunk)
-        heap->chunk = H5FL_BLK_FREE(lheap_chunk, heap->chunk);
-    while(heap->freelist) {
-        fl = heap->freelist;
-        heap->freelist = fl->next;
-        fl = H5FL_FREE(H5HL_free_t, fl);
-    } /* end while */
-    heap = H5FL_FREE(H5HL_t, heap);
+    /* Destroy local heap data block */
+    if(H5HL_dblk_dest(f, dblk) < 0)
+        HGOTO_ERROR(H5E_HEAP, H5E_CANTRELEASE, FAIL, "can't destroy local heap data block")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5HL_dest() */
+} /* end H5HL_datablock_dest() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5HL_clear
+ * Function:	H5HL_datablock_clear
  *
- * Purpose:	Mark a local heap in memory as non-dirty.
+ * Purpose:	Mark a local heap data block in memory as non-dirty.
  *
  * Return:	Non-negative on success/Negative on failure
  *
@@ -428,33 +775,35 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5HL_clear(H5F_t *f, H5HL_t *heap, hbool_t destroy)
+H5HL_datablock_clear(H5F_t *f, void *_thing, hbool_t destroy)
 {
+    H5HL_dblk_t *dblk = (H5HL_dblk_t *)_thing; /* Pointer to the local heap data block */
     herr_t ret_value = SUCCEED;         /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5HL_clear)
+    FUNC_ENTER_NOAPI_NOINIT(H5HL_datablock_clear)
 
     /* check arguments */
-    HDassert(heap);
+    HDassert(f);
+    HDassert(dblk);
 
-    /* Mark heap as clean */
-    heap->cache_info.is_dirty = FALSE;
+    /* Mark local heap data block as clean */
+    dblk->cache_info.is_dirty = FALSE;
 
     if(destroy)
-        if(H5HL_dest(f, heap) < 0)
-	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy local heap collection")
+        if(H5HL_dblk_dest(f, dblk) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy local heap data block")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5HL_clear() */
+} /* end H5HL_datablock_clear() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5HL_size
+ * Function:	H5HL_datablock_size
  *
- * Purpose:	Compute the size in bytes of the specified instance of
- *              H5HL_t on disk, and return it in *len_ptr.  On failure,
- *              the value of *len_ptr is undefined.
+ * Purpose:	Compute the size in bytes of the local heap data block on disk,
+ *              and return it in *len_ptr.  On failure, the value of *len_ptr
+ *              is undefined.
  *
  * Return:	Non-negative on success/Negative on failure
  *
@@ -463,18 +812,21 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-herr_t
-H5HL_size(const H5F_t *f, const H5HL_t *heap, size_t *size_ptr)
+static herr_t
+H5HL_datablock_size(const H5F_t UNUSED *f, const void *_thing, size_t *size_ptr)
 {
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HL_size)
+    const H5HL_dblk_t *dblk = (const H5HL_dblk_t *)_thing; /* Pointer to the local heap data block */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HL_datablock_size)
 
     /* check arguments */
-    HDassert(f);
-    HDassert(heap);
+    HDassert(dblk);
+    HDassert(dblk->heap);
     HDassert(size_ptr);
 
-    *size_ptr = H5HL_SIZEOF_HDR(f) + heap->heap_alloc;
+    /* Set size of data block in cache */
+    *size_ptr = dblk->heap->dblk_size;
 
     FUNC_LEAVE_NOAPI(SUCCEED)
-} /* H5HL_size() */
+} /* H5HL_datablock_size() */