1 /* 2 * Copyright (c) 2013, 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++ don'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 // Helper class to create an array of PaddedEnd<T> objects. All elements will 84 // start at a multiple of alignment and the size will be aligned to alignment. 85 template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE> 86 class PaddedArray { 87 public: 88 // Creates an aligned padded array. 89 // The memory can't be deleted since the raw memory chunk is not returned. 90 static PaddedEnd<T>* create_immortal(uint length); 91 }; 92 93 #endif // SHARE_VM_MEMORY_PADDED_HPP