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 ARM, x86-32, and 32-bit MIPS, 51 // it is the caller's responsibility to arrange for 64-bit 52 // alignment of 64-bit words accessed atomically. The first word in a 53 // variable or in an allocated struct, array, or slice can be relied upon to be 54 // 64-bit aligned. 55 56 // SwapInt32 atomically stores new into *addr and returns the previous *addr value. 57 func SwapInt32(addr *int32, new int32) (old int32) 58 59 // SwapInt64 atomically stores new into *addr and returns the previous *addr value. 60 func SwapInt64(addr *int64, new int64) (old int64) 61 62 // SwapUint32 atomically stores new into *addr and returns the previous *addr value. 63 func SwapUint32(addr *uint32, new uint32) (old uint32) 64 65 // SwapUint64 atomically stores new into *addr and returns the previous *addr value. 66 func SwapUint64(addr *uint64, new uint64) (old uint64) 67 68 // SwapUintptr atomically stores new into *addr and returns the previous *addr value. 69 func SwapUintptr(addr *uintptr, new uintptr) (old uintptr) 70 71 // SwapPointer atomically stores new into *addr and returns the previous *addr value. 72 func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer) 73 74 // CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value. 75 func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool) 76 77 // CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value. 78 func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool) 79 80 // CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value. 81 func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool) 82 83 // CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value. 84 func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool) 85 86 // CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value. 87 func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool) 88 89 // CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value. 90 func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool) 91 92 // AddInt32 atomically adds delta to *addr and returns the new value. 93 func AddInt32(addr *int32, delta int32) (new int32) 94 95 // AddUint32 atomically adds delta to *addr and returns the new value. 96 // To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)). 97 // In particular, to decrement x, do AddUint32(&x, ^uint32(0)). 98 func AddUint32(addr *uint32, delta uint32) (new uint32) 99 100 // AddInt64 atomically adds delta to *addr and returns the new value. 101 func AddInt64(addr *int64, delta int64) (new int64) 102 103 // AddUint64 atomically adds delta to *addr and returns the new value. 104 // To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)). 105 // In particular, to decrement x, do AddUint64(&x, ^uint64(0)). 106 func AddUint64(addr *uint64, delta uint64) (new uint64) 107 108 // AddUintptr atomically adds delta to *addr and returns the new value. 109 func AddUintptr(addr *uintptr, delta uintptr) (new uintptr) 110 111 // LoadInt32 atomically loads *addr. 112 func LoadInt32(addr *int32) (val int32) 113 114 // LoadInt64 atomically loads *addr. 115 func LoadInt64(addr *int64) (val int64) 116 117 // LoadUint32 atomically loads *addr. 118 func LoadUint32(addr *uint32) (val uint32) 119 120 // LoadUint64 atomically loads *addr. 121 func LoadUint64(addr *uint64) (val uint64) 122 123 // LoadUintptr atomically loads *addr. 124 func LoadUintptr(addr *uintptr) (val uintptr) 125 126 // LoadPointer atomically loads *addr. 127 func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer) 128 129 // StoreInt32 atomically stores val into *addr. 130 func StoreInt32(addr *int32, val int32) 131 132 // StoreInt64 atomically stores val into *addr. 133 func StoreInt64(addr *int64, val int64) 134 135 // StoreUint32 atomically stores val into *addr. 136 func StoreUint32(addr *uint32, val uint32) 137 138 // StoreUint64 atomically stores val into *addr. 139 func StoreUint64(addr *uint64, val uint64) 140 141 // StoreUintptr atomically stores val into *addr. 142 func StoreUintptr(addr *uintptr, val uintptr) 143 144 // StorePointer atomically stores val into *addr. 145 func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer) 146 147 // Helper for ARM. Linker will discard on other systems 148 func panic64() { 149 panic("sync/atomic: broken 64-bit atomic operations (buggy QEMU)") 150 } 151