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 Relaxed versions 18 // are provided when no fences are needed: 19 // Relaxed_Store() 20 // Relaxed_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 namespace v8 { 40 namespace base { 41 42 typedef char Atomic8; 43 typedef int32_t Atomic32; 44 #if defined(V8_HOST_ARCH_64_BIT) 45 // We need to be able to go between Atomic64 and AtomicWord implicitly. This 46 // means Atomic64 and AtomicWord should be the same type on 64-bit. 47 #if defined(__ILP32__) 48 typedef int64_t Atomic64; 49 #else 50 typedef intptr_t Atomic64; 51 #endif // defined(__ILP32__) 52 #endif // defined(V8_HOST_ARCH_64_BIT) 53 54 // Use AtomicWord for a machine-sized pointer. It will use the Atomic32 or 55 // Atomic64 routines below, depending on your architecture. 56 typedef intptr_t AtomicWord; 57 58 // Atomically execute: 59 // result = *ptr; 60 // if (*ptr == old_value) 61 // *ptr = new_value; 62 // return result; 63 // 64 // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value". 65 // Always return the old value of "*ptr" 66 // 67 // This routine implies no memory barriers. 68 Atomic32 Relaxed_CompareAndSwap(volatile Atomic32* ptr, Atomic32 old_value, 69 Atomic32 new_value); 70 71 // Atomically store new_value into *ptr, returning the previous value held in 72 // *ptr. This routine implies no memory barriers. 73 Atomic32 Relaxed_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value); 74 75 // Atomically increment *ptr by "increment". Returns the new value of 76 // *ptr with the increment applied. This routine implies no memory barriers. 77 Atomic32 Relaxed_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment); 78 79 Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr, 80 Atomic32 increment); 81 82 // These following lower-level operations are typically useful only to people 83 // implementing higher-level synchronization operations like spinlocks, 84 // mutexes, and condition-variables. They combine CompareAndSwap(), a load, 85 // or a store with appropriate memory-ordering instructions. "Acquire" 86 // operations ensure that no later memory access can be reordered ahead of the 87 // operation. "Release" operations ensure that no previous memory access can 88 // be reordered after the operation. "Fence" operations have both "Acquire" 89 // and "Release" semantics. A SeqCst_MemoryFence() has "Fence" semantics, but 90 // does no memory access. 91 Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr, 92 Atomic32 old_value, 93 Atomic32 new_value); 94 Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr, 95 Atomic32 old_value, 96 Atomic32 new_value); 97 98 void SeqCst_MemoryFence(); 99 void Relaxed_Store(volatile Atomic8* ptr, Atomic8 value); 100 void Relaxed_Store(volatile Atomic32* ptr, Atomic32 value); 101 void Release_Store(volatile Atomic32* ptr, Atomic32 value); 102 103 Atomic8 Relaxed_Load(volatile const Atomic8* ptr); 104 Atomic32 Relaxed_Load(volatile const Atomic32* ptr); 105 Atomic32 Acquire_Load(volatile const Atomic32* ptr); 106 107 // 64-bit atomic operations (only available on 64-bit processors). 108 #ifdef V8_HOST_ARCH_64_BIT 109 Atomic64 Relaxed_CompareAndSwap(volatile Atomic64* ptr, Atomic64 old_value, 110 Atomic64 new_value); 111 Atomic64 Relaxed_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value); 112 Atomic64 Relaxed_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment); 113 Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment); 114 115 Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr, 116 Atomic64 old_value, 117 Atomic64 new_value); 118 Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr, 119 Atomic64 old_value, 120 Atomic64 new_value); 121 void Relaxed_Store(volatile Atomic64* ptr, Atomic64 value); 122 void Release_Store(volatile Atomic64* ptr, Atomic64 value); 123 Atomic64 Relaxed_Load(volatile const Atomic64* ptr); 124 Atomic64 Acquire_Load(volatile const Atomic64* ptr); 125 #endif // V8_HOST_ARCH_64_BIT 126 127 } // namespace base 128 } // namespace v8 129 130 #if defined(V8_OS_WIN) 131 #include "src/base/atomicops_internals_std.h" 132 #else 133 // TODO(ulan): Switch to std version after performance regression with Wheezy 134 // sysroot is no longer relevant. Debian Wheezy LTS ends on 31st of May 2018. 135 #include "src/base/atomicops_internals_portable.h" 136 #endif 137 138 // On some platforms we need additional declarations to make 139 // AtomicWord compatible with our other Atomic* types. 140 #if defined(V8_OS_MACOSX) || defined(V8_OS_OPENBSD) || defined(V8_OS_AIX) 141 #include "src/base/atomicops_internals_atomicword_compat.h" 142 #endif 143 144 #endif // V8_BASE_ATOMICOPS_H_ 145
