1 // Copyright (c) 2012 The Chromium 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.
5 // For atomic operations on reference counts, see atomic_refcount.h.
6 // For atomic operations on sequence numbers, see atomic_sequence_num.h.
8 // The routines exported by this module are subtle. If you use them, even if
9 // you get the code right, it will depend on careful reasoning about atomicity
10 // and memory ordering; it will be less readable, and harder to maintain. If
11 // you plan to use these routines, you should have a good reason, such as solid
12 // evidence that performance would otherwise suffer, or there being no
13 // alternative. You should assume only properties explicitly guaranteed by the
14 // specifications in this file. You are almost certainly _not_ writing code
15 // just for the x86; if you assume x86 semantics, x86 hardware bugs and
16 // implementations on other archtectures will cause your code to break. If you
17 // do not know what you are doing, avoid these routines, and use a Mutex.
19 // It is incorrect to make direct assignments to/from an atomic variable.
20 // You should use one of the Load or Store routines. The NoBarrier
21 // versions are provided when no barriers are needed:
24 // Although there are currently no compiler enforcement, you are encouraged
28 #ifndef BASE_ATOMICOPS_H_
29 #define BASE_ATOMICOPS_H_
33 #include "build/build_config.h"
35 #if defined(OS_WIN) && defined(ARCH_CPU_64_BITS)
36 // windows.h #defines this (only on x64). This causes problems because the
37 // public API also uses MemoryBarrier at the public name for this fence. So, on
38 // X64, undef it, and call its documented
39 // (http://msdn.microsoft.com/en-us/library/windows/desktop/ms684208.aspx)
40 // implementation directly.
47 typedef int32_t Atomic32;
48 #ifdef ARCH_CPU_64_BITS
49 // We need to be able to go between Atomic64 and AtomicWord implicitly. This
50 // means Atomic64 and AtomicWord should be the same type on 64-bit.
51 #if defined(__ILP32__) || defined(OS_NACL)
52 // NaCl's intptr_t is not actually 64-bits on 64-bit!
53 // http://code.google.com/p/nativeclient/issues/detail?id=1162
54 typedef int64_t Atomic64;
56 typedef intptr_t Atomic64;
60 // Use AtomicWord for a machine-sized pointer. It will use the Atomic32 or
61 // Atomic64 routines below, depending on your architecture.
62 typedef intptr_t AtomicWord;
64 // Atomically execute:
66 // if (*ptr == old_value)
70 // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value".
71 // Always return the old value of "*ptr"
73 // This routine implies no memory barriers.
74 Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
78 // Atomically store new_value into *ptr, returning the previous value held in
79 // *ptr. This routine implies no memory barriers.
80 Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value);
82 // Atomically increment *ptr by "increment". Returns the new value of
83 // *ptr with the increment applied. This routine implies no memory barriers.
84 Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment);
86 Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
89 // These following lower-level operations are typically useful only to people
90 // implementing higher-level synchronization operations like spinlocks,
91 // mutexes, and condition-variables. They combine CompareAndSwap(), a load, or
92 // a store with appropriate memory-ordering instructions. "Acquire" operations
93 // ensure that no later memory access can be reordered ahead of the operation.
94 // "Release" operations ensure that no previous memory access can be reordered
95 // after the operation. "Barrier" operations have both "Acquire" and "Release"
96 // semantics. A MemoryBarrier() has "Barrier" semantics, but does no memory
98 Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
101 Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
105 void MemoryBarrier();
106 void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value);
107 void Acquire_Store(volatile Atomic32* ptr, Atomic32 value);
108 void Release_Store(volatile Atomic32* ptr, Atomic32 value);
110 Atomic32 NoBarrier_Load(volatile const Atomic32* ptr);
111 Atomic32 Acquire_Load(volatile const Atomic32* ptr);
112 Atomic32 Release_Load(volatile const Atomic32* ptr);
114 // 64-bit atomic operations (only available on 64-bit processors).
115 #ifdef ARCH_CPU_64_BITS
116 Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
119 Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value);
120 Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
121 Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
123 Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
126 Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
129 void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value);
130 void Acquire_Store(volatile Atomic64* ptr, Atomic64 value);
131 void Release_Store(volatile Atomic64* ptr, Atomic64 value);
132 Atomic64 NoBarrier_Load(volatile const Atomic64* ptr);
133 Atomic64 Acquire_Load(volatile const Atomic64* ptr);
134 Atomic64 Release_Load(volatile const Atomic64* ptr);
135 #endif // ARCH_CPU_64_BITS
137 } // namespace base::subtle
140 // Include our platform specific implementation.
141 #if defined(THREAD_SANITIZER)
142 #include "base/atomicops_internals_tsan.h"
143 #elif defined(OS_WIN) && defined(COMPILER_MSVC) && defined(ARCH_CPU_X86_FAMILY)
144 #include "base/atomicops_internals_x86_msvc.h"
145 #elif defined(OS_MACOSX)
146 #include "base/atomicops_internals_mac.h"
147 #elif defined(OS_NACL)
148 #include "base/atomicops_internals_gcc.h"
149 #elif defined(COMPILER_GCC) && defined(ARCH_CPU_ARM_FAMILY)
150 #include "base/atomicops_internals_arm_gcc.h"
151 #elif defined(COMPILER_GCC) && defined(ARCH_CPU_X86_FAMILY)
152 #include "base/atomicops_internals_x86_gcc.h"
153 #elif defined(COMPILER_GCC) && defined(ARCH_CPU_MIPS_FAMILY)
154 #include "base/atomicops_internals_mips_gcc.h"
156 #error "Atomic operations are not supported on your platform"
159 // On some platforms we need additional declarations to make
160 // AtomicWord compatible with our other Atomic* types.
161 #if defined(OS_MACOSX) || defined(OS_OPENBSD)
162 #include "base/atomicops_internals_atomicword_compat.h"
165 #endif // BASE_ATOMICOPS_H_