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 /*

  * Copyright (c) 2013, 2014, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 #ifndef SHARE_VM_MEMORY_PADDED_HPP

 #define SHARE_VM_MEMORY_PADDED_HPP

 #include "memory/allocation.hpp"

 #include "utilities/globalDefinitions.hpp"

 // Bytes needed to pad type to avoid cache-line sharing; alignment should be the

 // expected cache line size (a power of two).  The first addend avoids sharing

 // when the start address is not a multiple of alignment; the second maintains

 // alignment of starting addresses that happen to be a multiple.

 #define PADDING_SIZE(type, alignment)                           \

   ((alignment) + align_size_up_(sizeof(type), alignment))

 // Templates to create a subclass padded to avoid cache line sharing.  These are

 // effective only when applied to derived-most (leaf) classes.

 // When no args are passed to the base ctor.

 template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>

 class Padded : public T {

  private:

   char _pad_buf_[PADDING_SIZE(T, alignment)];

 };

 // When either 0 or 1 args may be passed to the base ctor.

 template <class T, typename Arg1T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>

 class Padded01 : public T {

  public:

   Padded01(): T() { }

   Padded01(Arg1T arg1): T(arg1) { }

  private:

   char _pad_buf_[PADDING_SIZE(T, alignment)];

 };

 // Super class of PaddedEnd when pad_size != 0.

 template <class T, size_t pad_size>

 class PaddedEndImpl : public T {

  private:

   char _pad_buf[pad_size];

 };

 // Super class of PaddedEnd when pad_size == 0.

 template <class T>

 class PaddedEndImpl<T, /*pad_size*/ 0> : public T {

   // No padding.

 };

 #define PADDED_END_SIZE(type, alignment) (align_size_up_(sizeof(type), alignment) - sizeof(type))

 // More memory conservative implementation of Padded. The subclass adds the

 // minimal amount of padding needed to make the size of the objects be aligned.

 // This will help reducing false sharing,

 // if the start address is a multiple of alignment.

 template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>

 class PaddedEnd : public PaddedEndImpl<T, PADDED_END_SIZE(T, alignment)> {

   // C++ don't allow zero-length arrays. The padding is put in a

   // super class that is specialized for the pad_size == 0 case.

 };

 // Helper class to create an array of PaddedEnd<T> objects. All elements will

 // start at a multiple of alignment and the size will be aligned to alignment.

 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>

 class PaddedArray {

  public:

   // Creates an aligned padded array.

   // The memory can't be deleted since the raw memory chunk is not returned.

   static PaddedEnd<T>* create_unfreeable(uint length);

 };

 // Helper class to create an array of references to arrays of primitive types

 // Both the array of references and the data arrays are aligned to the given

 // alignment. The allocated memory is zero-filled.

 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>

 class Padded2DArray {

  public:

   // Creates an aligned padded 2D array.

   // The memory cannot be deleted since the raw memory chunk is not returned.

   static T** create_unfreeable(uint rows, uint columns, size_t* allocation_size = NULL);

 };

 // Helper class to create an array of T objects. The array as a whole will

 // start at a multiple of alignment and its size will be aligned to alignment.

 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>

 class PaddedPrimitiveArray {

  public:

   static T* create_unfreeable(size_t length);

 };

 #endif // SHARE_VM_MEMORY_PADDED_HPP