/*

 * Copyright 2002-2008 Sun Microsystems, Inc.  All Rights Reserved.

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

 *

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

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

 * published by the Free Software Foundation.

 *

 * This code 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 General Public License

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

 * accompanied this code).

 *

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

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

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

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 *

 */

//

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

//

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

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

//

const int PREFETCH_QUEUE_SIZE  = 8;

class PrefetchQueue : public CHeapObj {

 private:

  void* _prefetch_queue[PREFETCH_QUEUE_SIZE];

  uint  _prefetch_index;

 public:

  int length() { return PREFETCH_QUEUE_SIZE; }

  inline void clear() {

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

      _prefetch_queue[i] = NULL;

    }

    _prefetch_index = 0;

  }

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

    oop o = oopDesc::load_decode_heap_oop_not_null(p);

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

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

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

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

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

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

    _prefetch_queue[_prefetch_index++] = p;

    _prefetch_index &= (PREFETCH_QUEUE_SIZE-1);

    return _prefetch_queue[_prefetch_index];

  }

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

  inline void* pop() {

    _prefetch_queue[_prefetch_index++] = NULL;

    _prefetch_index &= (PREFETCH_QUEUE_SIZE-1);

    return _prefetch_queue[_prefetch_index];

  }

};