1 /*
   2  * Copyright (c) 2013, 2014, 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 #ifndef SHARE_VM_MEMORY_PADDED_HPP
  26 #define SHARE_VM_MEMORY_PADDED_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "utilities/globalDefinitions.hpp"
  30 
  31 // Bytes needed to pad type to avoid cache-line sharing; alignment should be the
  32 // expected cache line size (a power of two).  The first addend avoids sharing
  33 // when the start address is not a multiple of alignment; the second maintains
  34 // alignment of starting addresses that happen to be a multiple.
  35 #define PADDING_SIZE(type, alignment)                           \
  36   ((alignment) + align_size_up_(sizeof(type), alignment))
  37 
  38 // Templates to create a subclass padded to avoid cache line sharing.  These are
  39 // effective only when applied to derived-most (leaf) classes.
  40 
  41 // When no args are passed to the base ctor.
  42 template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
  43 class Padded : public T {
  44  private:
  45   char _pad_buf_[PADDING_SIZE(T, alignment)];
  46 };
  47 
  48 // When either 0 or 1 args may be passed to the base ctor.
  49 template <class T, typename Arg1T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
  50 class Padded01 : public T {
  51  public:
  52   Padded01(): T() { }
  53   Padded01(Arg1T arg1): T(arg1) { }
  54  private:
  55   char _pad_buf_[PADDING_SIZE(T, alignment)];
  56 };
  57 
  58 // Super class of PaddedEnd when pad_size != 0.
  59 template <class T, size_t pad_size>
  60 class PaddedEndImpl : public T {
  61  private:
  62   char _pad_buf[pad_size];
  63 };
  64 
  65 // Super class of PaddedEnd when pad_size == 0.
  66 template <class T>
  67 class PaddedEndImpl<T, /*pad_size*/ 0> : public T {
  68   // No padding.
  69 };
  70 
  71 #define PADDED_END_SIZE(type, alignment) (align_size_up_(sizeof(type), alignment) - sizeof(type))
  72 
  73 // More memory conservative implementation of Padded. The subclass adds the
  74 // minimal amount of padding needed to make the size of the objects be aligned.
  75 // This will help reducing false sharing,
  76 // if the start address is a multiple of alignment.
  77 template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
  78 class PaddedEnd : public PaddedEndImpl<T, PADDED_END_SIZE(T, alignment)> {
  79   // C++ doesn't allow zero-length arrays. The padding is put in a
  80   // super class that is specialized for the pad_size == 0 case.
  81 };
  82 
  83 // Similar to PaddedEnd, this macro defines a _pad_buf#id field
  84 // that is (alignment - size) bytes in size. This macro is used
  85 // to add padding in between non-class fields in a class or struct.
  86 #define DEFINE_PAD_MINUS_SIZE(id, alignment, size) \
  87           char _pad_buf##id[(alignment) - (size)]
  88 
  89 // Helper class to create an array of PaddedEnd<T> objects. All elements will
  90 // start at a multiple of alignment and the size will be aligned to alignment.
  91 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
  92 class PaddedArray {
  93  public:
  94   // Creates an aligned padded array.
  95   // The memory can't be deleted since the raw memory chunk is not returned.
  96   static PaddedEnd<T>* create_unfreeable(uint length);
  97 };
  98 
  99 // Helper class to create an array of references to arrays of primitive types
 100 // Both the array of references and the data arrays are aligned to the given
 101 // alignment. The allocated memory is zero-filled.
 102 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
 103 class Padded2DArray {
 104  public:
 105   // Creates an aligned padded 2D array.
 106   // The memory cannot be deleted since the raw memory chunk is not returned.
 107   static T** create_unfreeable(uint rows, uint columns, size_t* allocation_size = NULL);
 108 };
 109 
 110 // Helper class to create an array of T objects. The array as a whole will
 111 // start at a multiple of alignment and its size will be aligned to alignment.
 112 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
 113 class PaddedPrimitiveArray {
 114  public:
 115   static T* create_unfreeable(size_t length);
 116 };
 117 
 118 #endif // SHARE_VM_MEMORY_PADDED_HPP