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.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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24
25 #ifndef SHARE_VM_MEMORY_PADDED_HPP
26 #define SHARE_VM_MEMORY_PADDED_HPP
27
28 #include "memory/allocation.hpp"
29 #include "utilities/align.hpp"
30 #include "utilities/globalDefinitions.hpp"
31
32 // Bytes needed to pad type to avoid cache-line sharing; alignment should be the
33 // expected cache line size (a power of two). The first addend avoids sharing
34 // when the start address is not a multiple of alignment; the second maintains
35 // alignment of starting addresses that happen to be a multiple.
36 #define PADDING_SIZE(type, alignment) \
37 ((alignment) + align_up_(sizeof(type), (alignment)))
38
39 // Templates to create a subclass padded to avoid cache line sharing. These are
40 // effective only when applied to derived-most (leaf) classes.
41
42 // When no args are passed to the base ctor.
43 template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
44 class Padded : public T {
45 private:
46 char _pad_buf_[PADDING_SIZE(T, alignment)];
47 };
48
49 // When either 0 or 1 args may be passed to the base ctor.
50 template <class T, typename Arg1T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
51 class Padded01 : public T {
52 public:
53 Padded01(): T() { }
54 Padded01(Arg1T arg1): T(arg1) { }
55 private:
56 char _pad_buf_[PADDING_SIZE(T, alignment)];
57 };
58
59 // Super class of PaddedEnd when pad_size != 0.
60 template <class T, size_t pad_size>
61 class PaddedEndImpl : public T {
62 private:
63 char _pad_buf[pad_size];
64 };
65
66 // Super class of PaddedEnd when pad_size == 0.
67 template <class T>
68 class PaddedEndImpl<T, /*pad_size*/ 0> : public T {
69 // No padding.
70 };
71
72 #define PADDED_END_SIZE(type, alignment) (align_up_(sizeof(type), (alignment)) - sizeof(type))
73
74 // More memory conservative implementation of Padded. The subclass adds the
75 // minimal amount of padding needed to make the size of the objects be aligned.
76 // This will help reducing false sharing,
77 // if the start address is a multiple of alignment.
78 template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
79 class PaddedEnd : public PaddedEndImpl<T, PADDED_END_SIZE(T, alignment)> {
80 // C++ doesn't allow zero-length arrays. The padding is put in a
81 // super class that is specialized for the pad_size == 0 case.
82 };
83
84 // Similar to PaddedEnd, this macro defines a _pad_buf#id field
85 // that is (alignment - size) bytes in size. This macro is used
86 // to add padding in between non-class fields in a class or struct.
87 #define DEFINE_PAD_MINUS_SIZE(id, alignment, size) \
88 char _pad_buf##id[(alignment) - (size)]
89
90 // Helper class to create an array of PaddedEnd<T> objects. All elements will
91 // start at a multiple of alignment and the size will be aligned to alignment.
92 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
93 class PaddedArray {
94 public:
95 // Creates an aligned padded array.
96 // The memory can't be deleted since the raw memory chunk is not returned.
97 static PaddedEnd<T>* create_unfreeable(uint length);
98 };
99
100 // Helper class to create an array of references to arrays of primitive types
101 // Both the array of references and the data arrays are aligned to the given
102 // alignment. The allocated memory is zero-filled.
103 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
104 class Padded2DArray {
105 public:
106 // Creates an aligned padded 2D array.
107 // The memory cannot be deleted since the raw memory chunk is not returned.
108 static T** create_unfreeable(uint rows, uint columns, size_t* allocation_size = NULL);
109 };
110
111 // Helper class to create an array of T objects. The array as a whole will
112 // start at a multiple of alignment and its size will be aligned to alignment.
113 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
114 class PaddedPrimitiveArray {
115 public:
116 static T* create_unfreeable(size_t length);
117 };
118
119 #endif // SHARE_VM_MEMORY_PADDED_HPP