1 /*

     2  * Copyright (c) 2002, 2008, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 //

    26 // PrefetchQueue is a FIFO queue of variable length (currently 8).

    27 //

    28 // We need to examine the performance penalty of variable lengths.

    29 // We may also want to split this into cpu dependent bits.

    30 //

    31 

    32 const int PREFETCH_QUEUE_SIZE  = 8;

    33 

    34 class PrefetchQueue : public CHeapObj {

    35  private:

    36   void* _prefetch_queue[PREFETCH_QUEUE_SIZE];

    37   uint  _prefetch_index;

    38 

    39  public:

    40   int length() { return PREFETCH_QUEUE_SIZE; }

    41 

    42   inline void clear() {

    43     for(int i=0; i<PREFETCH_QUEUE_SIZE; i++) {

    44       _prefetch_queue[i] = NULL;

    45     }

    46     _prefetch_index = 0;

    47   }

    48 

    49   template <class T> inline void* push_and_pop(T* p) {

    50     oop o = oopDesc::load_decode_heap_oop_not_null(p);

    51     Prefetch::write(o->mark_addr(), 0);

    52     // This prefetch is intended to make sure the size field of array

    53     // oops is in cache. It assumes the the object layout is

    54     // mark -> klass -> size, and that mark and klass are heapword

    55     // sized. If this should change, this prefetch will need updating!

    56     Prefetch::write(o->mark_addr() + (HeapWordSize*2), 0);

    57     _prefetch_queue[_prefetch_index++] = p;

    58     _prefetch_index &= (PREFETCH_QUEUE_SIZE-1);

    59     return _prefetch_queue[_prefetch_index];

    60   }

    61 

    62   // Stores a NULL pointer in the pop'd location.

    63   inline void* pop() {

    64     _prefetch_queue[_prefetch_index++] = NULL;

    65     _prefetch_index &= (PREFETCH_QUEUE_SIZE-1);

    66     return _prefetch_queue[_prefetch_index];

    67   }

    68 };