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 package atomic 41 42 import ( 43 "unsafe" 44 ) 45 46 // BUG(rsc): On x86-32, the 64-bit functions use instructions unavailable before the Pentium MMX. 47 // 48 // On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core. 49 // 50 // On both ARM and x86-32, it is the caller's responsibility to arrange for 64-bit 51 // alignment of 64-bit words accessed atomically. The first word in a global 52 // variable or in an allocated struct or slice can be relied upon to be 53 // 64-bit aligned. 54 55 // SwapInt32 atomically stores new into *addr and returns the previous *addr value. 56 func SwapInt32(addr *int32, new int32) (old int32) 57 58 // SwapInt64 atomically stores new into *addr and returns the previous *addr value. 59 func SwapInt64(addr *int64, new int64) (old int64) 60 61 // SwapUint32 atomically stores new into *addr and returns the previous *addr value. 62 func SwapUint32(addr *uint32, new uint32) (old uint32) 63 64 // SwapUint64 atomically stores new into *addr and returns the previous *addr value. 65 func SwapUint64(addr *uint64, new uint64) (old uint64) 66 67 // SwapUintptr atomically stores new into *addr and returns the previous *addr value. 68 func SwapUintptr(addr *uintptr, new uintptr) (old uintptr) 69 70 // SwapPointer atomically stores new into *addr and returns the previous *addr value. 71 func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer) 72 73 // CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value. 74 func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool) 75 76 // CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value. 77 func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool) 78 79 // CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value. 80 func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool) 81 82 // CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value. 83 func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool) 84 85 // CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value. 86 func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool) 87 88 // CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value. 89 func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool) 90 91 // AddInt32 atomically adds delta to *addr and returns the new value. 92 func AddInt32(addr *int32, delta int32) (new int32) 93 94 // AddUint32 atomically adds delta to *addr and returns the new value. 95 // To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)). 96 // In particular, to decrement x, do AddUint32(&x, ^uint32(0)). 97 func AddUint32(addr *uint32, delta uint32) (new uint32) 98 99 // AddInt64 atomically adds delta to *addr and returns the new value. 100 func AddInt64(addr *int64, delta int64) (new int64) 101 102 // AddUint64 atomically adds delta to *addr and returns the new value. 103 // To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)). 104 // In particular, to decrement x, do AddUint64(&x, ^uint64(0)). 105 func AddUint64(addr *uint64, delta uint64) (new uint64) 106 107 // AddUintptr atomically adds delta to *addr and returns the new value. 108 func AddUintptr(addr *uintptr, delta uintptr) (new uintptr) 109 110 // LoadInt32 atomically loads *addr. 111 func LoadInt32(addr *int32) (val int32) 112 113 // LoadInt64 atomically loads *addr. 114 func LoadInt64(addr *int64) (val int64) 115 116 // LoadUint32 atomically loads *addr. 117 func LoadUint32(addr *uint32) (val uint32) 118 119 // LoadUint64 atomically loads *addr. 120 func LoadUint64(addr *uint64) (val uint64) 121 122 // LoadUintptr atomically loads *addr. 123 func LoadUintptr(addr *uintptr) (val uintptr) 124 125 // LoadPointer atomically loads *addr. 126 func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer) 127 128 // StoreInt32 atomically stores val into *addr. 129 func StoreInt32(addr *int32, val int32) 130 131 // StoreInt64 atomically stores val into *addr. 132 func StoreInt64(addr *int64, val int64) 133 134 // StoreUint32 atomically stores val into *addr. 135 func StoreUint32(addr *uint32, val uint32) 136 137 // StoreUint64 atomically stores val into *addr. 138 func StoreUint64(addr *uint64, val uint64) 139 140 // StoreUintptr atomically stores val into *addr. 141 func StoreUintptr(addr *uintptr, val uintptr) 142 143 // StorePointer atomically stores val into *addr. 144 func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer) 145 146 // Helper for ARM. Linker will discard on other systems 147 func panic64() { 148 panic("sync/atomic: broken 64-bit atomic operations (buggy QEMU)") 149 } 150
