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

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 * 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.

 *

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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);

};

#endif // SHARE_VM_MEMORY_PADDED_HPP