Source file src/sync/atomic/doc.go
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 // 48 // [the Go memory model]: https://go.dev/ref/mem 49 package atomic 50 51 import ( 52 "unsafe" 53 ) 54 55 // BUG(rsc): On 386, the 64-bit functions use instructions unavailable before the Pentium MMX. 56 // 57 // On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core. 58 // 59 // On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange 60 // for 64-bit alignment of 64-bit words accessed atomically via the primitive 61 // atomic functions (types [Int64] and [Uint64] are automatically aligned). 62 // The first word in an allocated struct, array, or slice; in a global 63 // variable; or in a local variable (because the subject of all atomic operations 64 // will escape to the heap) can be relied upon to be 64-bit aligned. 65 66 // SwapInt32 atomically stores new into *addr and returns the previous *addr value. 67 // Consider using the more ergonomic and less error-prone [Int32.Swap] instead. 68 func SwapInt32(addr *int32, new int32) (old int32) 69 70 // SwapInt64 atomically stores new into *addr and returns the previous *addr value. 71 // Consider using the more ergonomic and less error-prone [Int64.Swap] instead 72 // (particularly if you target 32-bit platforms; see the bugs section). 73 func SwapInt64(addr *int64, new int64) (old int64) 74 75 // SwapUint32 atomically stores new into *addr and returns the previous *addr value. 76 // Consider using the more ergonomic and less error-prone [Uint32.Swap] instead. 77 func SwapUint32(addr *uint32, new uint32) (old uint32) 78 79 // SwapUint64 atomically stores new into *addr and returns the previous *addr value. 80 // Consider using the more ergonomic and less error-prone [Uint64.Swap] instead 81 // (particularly if you target 32-bit platforms; see the bugs section). 82 func SwapUint64(addr *uint64, new uint64) (old uint64) 83 84 // SwapUintptr atomically stores new into *addr and returns the previous *addr value. 85 // Consider using the more ergonomic and less error-prone [Uintptr.Swap] instead. 86 func SwapUintptr(addr *uintptr, new uintptr) (old uintptr) 87 88 // SwapPointer atomically stores new into *addr and returns the previous *addr value. 89 // Consider using the more ergonomic and less error-prone [Pointer.Swap] instead. 90 func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer) 91 92 // CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value. 93 // Consider using the more ergonomic and less error-prone [Int32.CompareAndSwap] instead. 94 func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool) 95 96 // CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value. 97 // Consider using the more ergonomic and less error-prone [Int64.CompareAndSwap] instead 98 // (particularly if you target 32-bit platforms; see the bugs section). 99 func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool) 100 101 // CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value. 102 // Consider using the more ergonomic and less error-prone [Uint32.CompareAndSwap] instead. 103 func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool) 104 105 // CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value. 106 // Consider using the more ergonomic and less error-prone [Uint64.CompareAndSwap] instead 107 // (particularly if you target 32-bit platforms; see the bugs section). 108 func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool) 109 110 // CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value. 111 // Consider using the more ergonomic and less error-prone [Uintptr.CompareAndSwap] instead. 112 func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool) 113 114 // CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value. 115 // Consider using the more ergonomic and less error-prone [Pointer.CompareAndSwap] instead. 116 func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool) 117 118 // AddInt32 atomically adds delta to *addr and returns the new value. 119 // Consider using the more ergonomic and less error-prone [Int32.Add] instead. 120 func AddInt32(addr *int32, delta int32) (new int32) 121 122 // AddUint32 atomically adds delta to *addr and returns the new value. 123 // To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)). 124 // In particular, to decrement x, do AddUint32(&x, ^uint32(0)). 125 // Consider using the more ergonomic and less error-prone [Uint32.Add] instead. 126 func AddUint32(addr *uint32, delta uint32) (new uint32) 127 128 // AddInt64 atomically adds delta to *addr and returns the new value. 129 // Consider using the more ergonomic and less error-prone [Int64.Add] instead 130 // (particularly if you target 32-bit platforms; see the bugs section). 131 func AddInt64(addr *int64, delta int64) (new int64) 132 133 // AddUint64 atomically adds delta to *addr and returns the new value. 134 // To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)). 135 // In particular, to decrement x, do AddUint64(&x, ^uint64(0)). 136 // Consider using the more ergonomic and less error-prone [Uint64.Add] instead 137 // (particularly if you target 32-bit platforms; see the bugs section). 138 func AddUint64(addr *uint64, delta uint64) (new uint64) 139 140 // AddUintptr atomically adds delta to *addr and returns the new value. 141 // Consider using the more ergonomic and less error-prone [Uintptr.Add] instead. 142 func AddUintptr(addr *uintptr, delta uintptr) (new uintptr) 143 144 // AndInt32 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask 145 // and returns the old value. 146 // Consider using the more ergonomic and less error-prone [Int32.And] instead. 147 func AndInt32(addr *int32, mask int32) (old int32) 148 149 // AndUint32 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask 150 // and returns the old value. 151 // Consider using the more ergonomic and less error-prone [Uint32.And] instead. 152 func AndUint32(addr *uint32, mask uint32) (old uint32) 153 154 // AndInt64 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask 155 // and returns the old value. 156 // Consider using the more ergonomic and less error-prone [Int64.And] instead. 157 func AndInt64(addr *int64, mask int64) (old int64) 158 159 // AndUint64 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask 160 // and returns the old. 161 // Consider using the more ergonomic and less error-prone [Uint64.And] instead. 162 func AndUint64(addr *uint64, mask uint64) (old uint64) 163 164 // AndUintptr atomically performs a bitwise AND operation on *addr using the bitmask provided as mask 165 // and returns the old value. 166 // Consider using the more ergonomic and less error-prone [Uintptr.And] instead. 167 func AndUintptr(addr *uintptr, mask uintptr) (old uintptr) 168 169 // OrInt32 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask 170 // and returns the old value. 171 // Consider using the more ergonomic and less error-prone [Int32.Or] instead. 172 func OrInt32(addr *int32, mask int32) (old int32) 173 174 // OrUint32 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask 175 // and returns the old value. 176 // Consider using the more ergonomic and less error-prone [Uint32.Or] instead. 177 func OrUint32(addr *uint32, mask uint32) (old uint32) 178 179 // OrInt64 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask 180 // and returns the old value. 181 // Consider using the more ergonomic and less error-prone [Int64.Or] instead. 182 func OrInt64(addr *int64, mask int64) (old int64) 183 184 // OrUint64 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask 185 // and returns the old value. 186 // Consider using the more ergonomic and less error-prone [Uint64.Or] instead. 187 func OrUint64(addr *uint64, mask uint64) (old uint64) 188 189 // OrUintptr atomically performs a bitwise OR operation on *addr using the bitmask provided as mask 190 // and returns the old value. 191 // Consider using the more ergonomic and less error-prone [Uintptr.Or] instead. 192 func OrUintptr(addr *uintptr, mask uintptr) (old uintptr) 193 194 // LoadInt32 atomically loads *addr. 195 // Consider using the more ergonomic and less error-prone [Int32.Load] instead. 196 func LoadInt32(addr *int32) (val int32) 197 198 // LoadInt64 atomically loads *addr. 199 // Consider using the more ergonomic and less error-prone [Int64.Load] instead 200 // (particularly if you target 32-bit platforms; see the bugs section). 201 func LoadInt64(addr *int64) (val int64) 202 203 // LoadUint32 atomically loads *addr. 204 // Consider using the more ergonomic and less error-prone [Uint32.Load] instead. 205 func LoadUint32(addr *uint32) (val uint32) 206 207 // LoadUint64 atomically loads *addr. 208 // Consider using the more ergonomic and less error-prone [Uint64.Load] instead 209 // (particularly if you target 32-bit platforms; see the bugs section). 210 func LoadUint64(addr *uint64) (val uint64) 211 212 // LoadUintptr atomically loads *addr. 213 // Consider using the more ergonomic and less error-prone [Uintptr.Load] instead. 214 func LoadUintptr(addr *uintptr) (val uintptr) 215 216 // LoadPointer atomically loads *addr. 217 // Consider using the more ergonomic and less error-prone [Pointer.Load] instead. 218 func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer) 219 220 // StoreInt32 atomically stores val into *addr. 221 // Consider using the more ergonomic and less error-prone [Int32.Store] instead. 222 func StoreInt32(addr *int32, val int32) 223 224 // StoreInt64 atomically stores val into *addr. 225 // Consider using the more ergonomic and less error-prone [Int64.Store] instead 226 // (particularly if you target 32-bit platforms; see the bugs section). 227 func StoreInt64(addr *int64, val int64) 228 229 // StoreUint32 atomically stores val into *addr. 230 // Consider using the more ergonomic and less error-prone [Uint32.Store] instead. 231 func StoreUint32(addr *uint32, val uint32) 232 233 // StoreUint64 atomically stores val into *addr. 234 // Consider using the more ergonomic and less error-prone [Uint64.Store] instead 235 // (particularly if you target 32-bit platforms; see the bugs section). 236 func StoreUint64(addr *uint64, val uint64) 237 238 // StoreUintptr atomically stores val into *addr. 239 // Consider using the more ergonomic and less error-prone [Uintptr.Store] instead. 240 func StoreUintptr(addr *uintptr, val uintptr) 241 242 // StorePointer atomically stores val into *addr. 243 // Consider using the more ergonomic and less error-prone [Pointer.Store] instead. 244 func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer) 245