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Java example source code file (padded.hpp)

This example Java source code file (padded.hpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

arg1t, default_cache_line_size, memflags, padded01, padded_end_size, paddedarray, paddedendimpl, padding_size, share_vm_memory_padded_hpp

The padded.hpp Java example source code

/*
 * Copyright (c) 2013, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#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

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