1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package atomic provides low-level atomic memory primitives 6 // useful for implementing synchronization algorithms. 7 // 8 // These functions require great care to be used correctly. 9 // Except for special, low-level applications, synchronization is better 10 // done with channels or the facilities of the sync package. 11 // Share memory by communicating; 12 // don't communicate by sharing memory. 13 // 14 // The swap operation, implemented by the SwapT functions, is the atomic 15 // equivalent of: 16 // 17 // old = *addr 18 // *addr = new 19 // return old 20 // 21 // The compare-and-swap operation, implemented by the CompareAndSwapT 22 // functions, is the atomic equivalent of: 23 // 24 // if *addr == old { 25 // *addr = new 26 // return true 27 // } 28 // return false 29 // 30 // The add operation, implemented by the AddT functions, is the atomic 31 // equivalent of: 32 // 33 // *addr += delta 34 // return *addr 35 // 36 // The load and store operations, implemented by the LoadT and StoreT 37 // functions, are the atomic equivalents of "return *addr" and 38 // "*addr = val". 39 // 40 // In the terminology of the Go memory model, if the effect of 41 // an atomic operation A is observed by atomic operation B, 42 // then A “synchronizes before” B. 43 // Additionally, all the atomic operations executed in a program 44 // behave as though executed in some sequentially consistent order. 45 // This definition provides the same semantics as 46 // C++'s sequentially consistent atomics and Java's volatile variables. 47 package atomic 48 49 import ( 50 "unsafe" 51 ) 52 53 // BUG(rsc): On 386, the 64-bit functions use instructions unavailable before the Pentium MMX. 54 // 55 // On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core. 56 // 57 // On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange 58 // for 64-bit alignment of 64-bit words accessed atomically via the primitive 59 // atomic functions (types Int64 and Uint64 are automatically aligned). 60 // The first word in an allocated struct, array, or slice; in a global 61 // variable; or in a local variable (because the subject of all atomic operations 62 // will escape to the heap) can be relied upon to be 64-bit aligned. 63 64 // SwapInt32 atomically stores new into *addr and returns the previous *addr value. 65 func SwapInt32(addr *int32, new int32) (old int32) 66 67 // SwapInt64 atomically stores new into *addr and returns the previous *addr value. 68 func SwapInt64(addr *int64, new int64) (old int64) 69 70 // SwapUint32 atomically stores new into *addr and returns the previous *addr value. 71 func SwapUint32(addr *uint32, new uint32) (old uint32) 72 73 // SwapUint64 atomically stores new into *addr and returns the previous *addr value. 74 func SwapUint64(addr *uint64, new uint64) (old uint64) 75 76 // SwapUintptr atomically stores new into *addr and returns the previous *addr value. 77 func SwapUintptr(addr *uintptr, new uintptr) (old uintptr) 78 79 // SwapPointer atomically stores new into *addr and returns the previous *addr value. 80 func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer) 81 82 // CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value. 83 func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool) 84 85 // CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value. 86 func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool) 87 88 // CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value. 89 func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool) 90 91 // CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value. 92 func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool) 93 94 // CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value. 95 func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool) 96 97 // CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value. 98 func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool) 99 100 // AddInt32 atomically adds delta to *addr and returns the new value. 101 func AddInt32(addr *int32, delta int32) (new int32) 102 103 // AddUint32 atomically adds delta to *addr and returns the new value. 104 // To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)). 105 // In particular, to decrement x, do AddUint32(&x, ^uint32(0)). 106 func AddUint32(addr *uint32, delta uint32) (new uint32) 107 108 // AddInt64 atomically adds delta to *addr and returns the new value. 109 func AddInt64(addr *int64, delta int64) (new int64) 110 111 // AddUint64 atomically adds delta to *addr and returns the new value. 112 // To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)). 113 // In particular, to decrement x, do AddUint64(&x, ^uint64(0)). 114 func AddUint64(addr *uint64, delta uint64) (new uint64) 115 116 // AddUintptr atomically adds delta to *addr and returns the new value. 117 func AddUintptr(addr *uintptr, delta uintptr) (new uintptr) 118 119 // LoadInt32 atomically loads *addr. 120 func LoadInt32(addr *int32) (val int32) 121 122 // LoadInt64 atomically loads *addr. 123 func LoadInt64(addr *int64) (val int64) 124 125 // LoadUint32 atomically loads *addr. 126 func LoadUint32(addr *uint32) (val uint32) 127 128 // LoadUint64 atomically loads *addr. 129 func LoadUint64(addr *uint64) (val uint64) 130 131 // LoadUintptr atomically loads *addr. 132 func LoadUintptr(addr *uintptr) (val uintptr) 133 134 // LoadPointer atomically loads *addr. 135 func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer) 136 137 // StoreInt32 atomically stores val into *addr. 138 func StoreInt32(addr *int32, val int32) 139 140 // StoreInt64 atomically stores val into *addr. 141 func StoreInt64(addr *int64, val int64) 142 143 // StoreUint32 atomically stores val into *addr. 144 func StoreUint32(addr *uint32, val uint32) 145 146 // StoreUint64 atomically stores val into *addr. 147 func StoreUint64(addr *uint64, val uint64) 148 149 // StoreUintptr atomically stores val into *addr. 150 func StoreUintptr(addr *uintptr, val uintptr) 151 152 // StorePointer atomically stores val into *addr. 153 func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer) 154