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 // Small C++ header which defines implementation specific macros used to
34 // identify the STL implementation.
35 // - libc++: captures __config for _LIBCPP_VERSION
36 // - libstdc++: captures bits/c++config.h for __GLIBCXX__
39 #include "base/base_export.h"
40 #include "build/build_config.h"
45 typedef int32_t Atomic32;
46 #ifdef ARCH_CPU_64_BITS
47 // We need to be able to go between Atomic64 and AtomicWord implicitly. This
48 // means Atomic64 and AtomicWord should be the same type on 64-bit.
49 #if defined(__ILP32__) || defined(OS_NACL)
50 // NaCl's intptr_t is not actually 64-bits on 64-bit!
51 // http://code.google.com/p/nativeclient/issues/detail?id=1162
52 typedef int64_t Atomic64;
54 typedef intptr_t Atomic64;
58 // Use AtomicWord for a machine-sized pointer. It will use the Atomic32 or
59 // Atomic64 routines below, depending on your architecture.
60 typedef intptr_t AtomicWord;
62 // Atomically execute:
64 // if (*ptr == old_value)
68 // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value".
69 // Always return the old value of "*ptr"
71 // This routine implies no memory barriers.
72 Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
76 // Atomically store new_value into *ptr, returning the previous value held in
77 // *ptr. This routine implies no memory barriers.
78 Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value);
80 // Atomically increment *ptr by "increment". Returns the new value of
81 // *ptr with the increment applied. This routine implies no memory barriers.
82 Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment);
84 Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
87 // These following lower-level operations are typically useful only to people
88 // implementing higher-level synchronization operations like spinlocks,
89 // mutexes, and condition-variables. They combine CompareAndSwap(), a load, or
90 // a store with appropriate memory-ordering instructions. "Acquire" operations
91 // ensure that no later memory access can be reordered ahead of the operation.
92 // "Release" operations ensure that no previous memory access can be reordered
93 // after the operation. "Barrier" operations have both "Acquire" and "Release"
95 Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
98 Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
102 void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value);
103 void Acquire_Store(volatile Atomic32* ptr, Atomic32 value);
104 void Release_Store(volatile Atomic32* ptr, Atomic32 value);
106 Atomic32 NoBarrier_Load(volatile const Atomic32* ptr);
107 Atomic32 Acquire_Load(volatile const Atomic32* ptr);
108 Atomic32 Release_Load(volatile const Atomic32* ptr);
110 // 64-bit atomic operations (only available on 64-bit processors).
111 #ifdef ARCH_CPU_64_BITS
112 Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
115 Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value);
116 Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
117 Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
119 Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
122 Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
125 void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value);
126 void Acquire_Store(volatile Atomic64* ptr, Atomic64 value);
127 void Release_Store(volatile Atomic64* ptr, Atomic64 value);
128 Atomic64 NoBarrier_Load(volatile const Atomic64* ptr);
129 Atomic64 Acquire_Load(volatile const Atomic64* ptr);
130 Atomic64 Release_Load(volatile const Atomic64* ptr);
131 #endif // ARCH_CPU_64_BITS
133 } // namespace subtle
136 #if defined(OS_WIN) && defined(ARCH_CPU_X86_FAMILY)
137 // TODO(jfb): Try to use base/atomicops_internals_portable.h everywhere.
138 // https://crbug.com/559247.
139 # include "base/atomicops_internals_x86_msvc.h"
141 # include "base/atomicops_internals_portable.h"
144 // On some platforms we need additional declarations to make
145 // AtomicWord compatible with our other Atomic* types.
146 #if defined(OS_MACOSX) || defined(OS_OPENBSD)
147 #include "base/atomicops_internals_atomicword_compat.h"
150 #endif // BASE_ATOMICOPS_H_