1 // Copyright 2010 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // The routines exported by this module are subtle. If you use them, even if 6 // you get the code right, it will depend on careful reasoning about atomicity 7 // and memory ordering; it will be less readable, and harder to maintain. If 8 // you plan to use these routines, you should have a good reason, such as solid 9 // evidence that performance would otherwise suffer, or there being no 10 // alternative. You should assume only properties explicitly guaranteed by the 11 // specifications in this file. You are almost certainly _not_ writing code 12 // just for the x86; if you assume x86 semantics, x86 hardware bugs and 13 // implementations on other archtectures will cause your code to break. If you 14 // do not know what you are doing, avoid these routines, and use a Mutex. 15 // 16 // It is incorrect to make direct assignments to/from an atomic variable. 17 // You should use one of the Load or Store routines. The NoBarrier 18 // versions are provided when no barriers are needed: 19 // NoBarrier_Store() 20 // NoBarrier_Load() 21 // Although there are currently no compiler enforcement, you are encouraged 22 // to use these. 23 // 24 25 #ifndef V8_BASE_ATOMICOPS_H_ 26 #define V8_BASE_ATOMICOPS_H_ 27 28 #include <stdint.h> 29 30 // Small C++ header which defines implementation specific macros used to 31 // identify the STL implementation. 32 // - libc++: captures __config for _LIBCPP_VERSION 33 // - libstdc++: captures bits/c++config.h for __GLIBCXX__ 34 #include <cstddef> 35 36 #include "src/base/base-export.h" 37 #include "src/base/build_config.h" 38 39 #if defined(V8_OS_WIN) && defined(V8_HOST_ARCH_64_BIT) 40 // windows.h #defines this (only on x64). This causes problems because the 41 // public API also uses MemoryBarrier at the public name for this fence. So, on 42 // X64, undef it, and call its documented 43 // (http://msdn.microsoft.com/en-us/library/windows/desktop/ms684208.aspx) 44 // implementation directly. 45 #undef MemoryBarrier 46 #endif 47 48 namespace v8 { 49 namespace base { 50 51 typedef char Atomic8; 52 typedef int32_t Atomic32; 53 #if defined(V8_HOST_ARCH_64_BIT) 54 // We need to be able to go between Atomic64 and AtomicWord implicitly. This 55 // means Atomic64 and AtomicWord should be the same type on 64-bit. 56 #if defined(__ILP32__) 57 typedef int64_t Atomic64; 58 #else 59 typedef intptr_t Atomic64; 60 #endif // defined(__ILP32__) 61 #endif // defined(V8_HOST_ARCH_64_BIT) 62 63 // Use AtomicWord for a machine-sized pointer. It will use the Atomic32 or 64 // Atomic64 routines below, depending on your architecture. 65 typedef intptr_t AtomicWord; 66 67 // Atomically execute: 68 // result = *ptr; 69 // if (*ptr == old_value) 70 // *ptr = new_value; 71 // return result; 72 // 73 // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value". 74 // Always return the old value of "*ptr" 75 // 76 // This routine implies no memory barriers. 77 Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr, 78 Atomic32 old_value, 79 Atomic32 new_value); 80 81 // Atomically store new_value into *ptr, returning the previous value held in 82 // *ptr. This routine implies no memory barriers. 83 Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value); 84 85 // Atomically increment *ptr by "increment". Returns the new value of 86 // *ptr with the increment applied. This routine implies no memory barriers. 87 Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment); 88 89 Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr, 90 Atomic32 increment); 91 92 // These following lower-level operations are typically useful only to people 93 // implementing higher-level synchronization operations like spinlocks, 94 // mutexes, and condition-variables. They combine CompareAndSwap(), a load, or 95 // a store with appropriate memory-ordering instructions. "Acquire" operations 96 // ensure that no later memory access can be reordered ahead of the operation. 97 // "Release" operations ensure that no previous memory access can be reordered 98 // after the operation. "Barrier" operations have both "Acquire" and "Release" 99 // semantics. A MemoryBarrier() has "Barrier" semantics, but does no memory 100 // access. 101 Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr, 102 Atomic32 old_value, 103 Atomic32 new_value); 104 Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr, 105 Atomic32 old_value, 106 Atomic32 new_value); 107 108 void MemoryBarrier(); 109 void NoBarrier_Store(volatile Atomic8* ptr, Atomic8 value); 110 void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value); 111 void Release_Store(volatile Atomic32* ptr, Atomic32 value); 112 113 Atomic8 NoBarrier_Load(volatile const Atomic8* ptr); 114 Atomic32 NoBarrier_Load(volatile const Atomic32* ptr); 115 Atomic32 Acquire_Load(volatile const Atomic32* ptr); 116 117 // 64-bit atomic operations (only available on 64-bit processors). 118 #ifdef V8_HOST_ARCH_64_BIT 119 Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr, 120 Atomic64 old_value, 121 Atomic64 new_value); 122 Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value); 123 Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment); 124 Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment); 125 126 Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr, 127 Atomic64 old_value, 128 Atomic64 new_value); 129 Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr, 130 Atomic64 old_value, 131 Atomic64 new_value); 132 void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value); 133 void Release_Store(volatile Atomic64* ptr, Atomic64 value); 134 Atomic64 NoBarrier_Load(volatile const Atomic64* ptr); 135 Atomic64 Acquire_Load(volatile const Atomic64* ptr); 136 #endif // V8_HOST_ARCH_64_BIT 137 138 } // namespace base 139 } // namespace v8 140 141 #if defined(V8_OS_WIN) 142 // TODO(hpayer): The MSVC header includes windows.h, which other files end up 143 // relying on. Fix this as part of crbug.com/559247. 144 #include "src/base/atomicops_internals_x86_msvc.h" 145 #else 146 #include "src/base/atomicops_internals_portable.h" 147 #endif 148 149 // On some platforms we need additional declarations to make 150 // AtomicWord compatible with our other Atomic* types. 151 #if defined(V8_OS_MACOSX) || defined(V8_OS_OPENBSD) || defined(V8_OS_AIX) 152 #include "src/base/atomicops_internals_atomicword_compat.h" 153 #endif 154 155 #endif // V8_BASE_ATOMICOPS_H_ 156
