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atomic
atomic 操作的对象是一个地址，你须要把可寻址的变量的地址作为参数传递给办法，而不是把变量的值传递给办法。
Add
// AddInt32 atomically adds delta to *addr and returns the new value.
// AddInt32 以原子形式将 delta 增加到 *addr 并返回新值。func AddInt32(addr *int32, delta int32) (new int32)
// AddUint32 atomically adds delta to *addr and returns the new value.
// To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)).
// In particular, to decrement x, do AddUint32(&x, ^uint32(0)).
// AddUint32 以原子形式将 delta 增加到 *addr 并返回新值。// 要从 x 中减去一个有符号的失常数值 c，请执行 AddUint32(&x, ^uint32(c-1))。// 特地是，要减 1，请执行 AddUint32(&x, ^uint32(0))
// AddInt64 atomically adds delta to *addr and returns the new value.
func AddInt64(addr *int64, delta int64) (new int64)
// AddUint64 atomically adds delta to *addr and returns the new value.
// To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)).
// In particular, to decrement x, do AddUint64(&x, ^uint64(0)).
func AddUint64(addr *uint64, delta uint64) (new uint64)
// AddUintptr atomically adds delta to *addr and returns the new value.
func AddUintptr(addr *uintptr, delta uintptr) (new uintptr)CAS
// CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value.
func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool)
// CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value.
func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool)
// CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value.
// CompareAndSwapInt32 对 int32 值执行比拟和替换操作。func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool)
// CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value.
func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool)
// CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value.
func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool)
// CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value.
func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool)比拟以后 addr 地址里的值是不是 old，如果不等于 old，就返回 false；如果等于 old，就把此地址的值替换成 new 值，返回 true。
Swap
如果不须要比拟旧值，只是比拟粗犷地替换的话，就能够应用 Swap 办法，它替换后还可
以返回旧值
// SwapInt32 atomically stores new into *addr and returns the previous *addr value.
func SwapInt32(addr *int32, new int32) (old int32)
// SwapInt64 atomically stores new into *addr and returns the previous *addr value.
// SwapInt32 以原子形式将 new 存储到 *addr 并返回之前的 *addr 值。func SwapInt64(addr *int64, new int64) (old int64)
// SwapUint32 atomically stores new into *addr and returns the previous *addr value.
func SwapUint32(addr *uint32, new uint32) (old uint32)
// SwapUint64 atomically stores new into *addr and returns the previous *addr value.
func SwapUint64(addr *uint64, new uint64) (old uint64)
// SwapUintptr atomically stores new into *addr and returns the previous *addr value.
func SwapUintptr(addr *uintptr, new uintptr) (old uintptr)
// SwapPointer atomically stores new into *addr and returns the previous *addr value.
func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer)Load
// LoadInt32 atomically loads *addr.
// LoadInt32 以原子形式加载 *addr。func LoadInt32(addr *int32) (val int32)
// LoadInt64 atomically loads *addr.
func LoadInt64(addr *int64) (val int64)
// LoadUint32 atomically loads *addr.
func LoadUint32(addr *uint32) (val uint32)
// LoadUint64 atomically loads *addr.
func LoadUint64(addr *uint64) (val uint64)
// LoadUintptr atomically loads *addr.
func LoadUintptr(addr *uintptr) (val uintptr)
// LoadPointer atomically loads *addr.
func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer)Store
// StoreInt32 atomically stores val into *addr.
// StoreInt32 以原子形式将 val 存储到 *addr。func StoreInt32(addr *int32, val int32)
// StoreInt64 atomically stores val into *addr.
func StoreInt64(addr *int64, val int64)
// StoreUint32 atomically stores val into *addr.
func StoreUint32(addr *uint32, val uint32)
// StoreUint64 atomically stores val into *addr.
func StoreUint64(addr *uint64, val uint64)
// StoreUintptr atomically stores val into *addr.
func StoreUintptr(addr *uintptr, val uintptr)
// StorePointer atomically stores val into *addr.
func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer)Value 类型
原子地存取对象类型，但也只能存取，不能 CAS 和 Swap，经常用在配置变更等场景
中。
// Value 提供了统一类型值的原子加载和存储。// Value 的零值从 Load 返回 nil。// 调用 Store 后，不得复制 Value。//
// 首次应用后不得复制 Value。type Value struct {v any}
// ifaceWords is interface{} internal representation.
// //ifaceWords 是 interface{} 外部示意。type ifaceWords struct {
typ unsafe.Pointer
data unsafe.Pointer
}Load
//Load 返回最近的 Store 设置的值。// 如果没有为此 value 调用 Store，则返回 nil。// Load returns the value set by the most recent Store.
// It returns nil if there has been no call to Store for this Value.
func (v *Value) Load() (val any) {vp := (*ifaceWords)(unsafe.Pointer(v))
typ := LoadPointer(&vp.typ)
if typ == nil || typ == unsafe.Pointer(&firstStoreInProgress) {
// First store not yet completed.
return nil
}
data := LoadPointer(&vp.data)
vlp := (*ifaceWords)(unsafe.Pointer(&val))
vlp.typ = typ
vlp.data = data
return
}store
var firstStoreInProgress byte
// Store sets the value of the Value to x.
// All calls to Store for a given Value must use values of the same concrete type.
// Store of an inconsistent type panics, as does Store(nil).
func (v *Value) Store(val any) {
if val == nil {panic("sync/atomic: store of nil value into Value")
}
vp := (*ifaceWords)(unsafe.Pointer(v))
vlp := (*ifaceWords)(unsafe.Pointer(&val))
for {typ := LoadPointer(&vp.typ)
if typ == nil {
// Attempt to start first store.
// Disable preemption so that other goroutines can use
// active spin wait to wait for completion.
runtime_procPin()
if !CompareAndSwapPointer(&vp.typ, nil, unsafe.Pointer(&firstStoreInProgress)) {runtime_procUnpin()
continue
}
// Complete first store.
StorePointer(&vp.data, vlp.data)
StorePointer(&vp.typ, vlp.typ)
runtime_procUnpin()
return
}
if typ == unsafe.Pointer(&firstStoreInProgress) {
// First store in progress. Wait.
// Since we disable preemption around the first store,
// we can wait with active spinning.
continue
}
// First store completed. Check type and overwrite data.
if typ != vlp.typ {panic("sync/atomic: store of inconsistently typed value into Value")
}
StorePointer(&vp.data, vlp.data)
return
}
}swap
// Swap stores new into Value and returns the previous value. It returns nil if
// the Value is empty.
//
// All calls to Swap for a given Value must use values of the same concrete
// type. Swap of an inconsistent type panics, as does Swap(nil).
func (v *Value) Swap(new any) (old any) {
if new == nil {panic("sync/atomic: swap of nil value into Value")
}
vp := (*ifaceWords)(unsafe.Pointer(v))
np := (*ifaceWords)(unsafe.Pointer(&new))
for {typ := LoadPointer(&vp.typ)
if typ == nil {
// Attempt to start first store.
// Disable preemption so that other goroutines can use
// active spin wait to wait for completion; and so that
// GC does not see the fake type accidentally.
runtime_procPin()
if !CompareAndSwapPointer(&vp.typ, nil, unsafe.Pointer(&firstStoreInProgress)) {runtime_procUnpin()
continue
}
// Complete first store.
StorePointer(&vp.data, np.data)
StorePointer(&vp.typ, np.typ)
runtime_procUnpin()
return nil
}
if typ == unsafe.Pointer(&firstStoreInProgress) {
// First store in progress. Wait.
// Since we disable preemption around the first store,
// we can wait with active spinning.
continue
}
// First store completed. Check type and overwrite data.
if typ != np.typ {panic("sync/atomic: swap of inconsistently typed value into Value")
}
op := (*ifaceWords)(unsafe.Pointer(&old))
op.typ, op.data = np.typ, SwapPointer(&vp.data, np.data)
return old
}
}cas
// CompareAndSwap executes the compare-and-swap operation for the Value.
//
// All calls to CompareAndSwap for a given Value must use values of the same
// concrete type. CompareAndSwap of an inconsistent type panics, as does
// CompareAndSwap(old, nil).
func (v *Value) CompareAndSwap(old, new any) (swapped bool) {
if new == nil {panic("sync/atomic: compare and swap of nil value into Value")
}
vp := (*ifaceWords)(unsafe.Pointer(v))
np := (*ifaceWords)(unsafe.Pointer(&new))
op := (*ifaceWords)(unsafe.Pointer(&old))
if op.typ != nil && np.typ != op.typ {panic("sync/atomic: compare and swap of inconsistently typed values")
}
for {typ := LoadPointer(&vp.typ)
if typ == nil {
if old != nil {return false}
// Attempt to start first store.
// Disable preemption so that other goroutines can use
// active spin wait to wait for completion; and so that
// GC does not see the fake type accidentally.
runtime_procPin()
if !CompareAndSwapPointer(&vp.typ, nil, unsafe.Pointer(&firstStoreInProgress)) {runtime_procUnpin()
continue
}
// Complete first store.
StorePointer(&vp.data, np.data)
StorePointer(&vp.typ, np.typ)
runtime_procUnpin()
return true
}
if typ == unsafe.Pointer(&firstStoreInProgress) {
// First store in progress. Wait.
// Since we disable preemption around the first store,
// we can wait with active spinning.
continue
}
// First store completed. Check type and overwrite data.
if typ != np.typ {panic("sync/atomic: compare and swap of inconsistently typed value into Value")
}
// Compare old and current via runtime equality check.
// This allows value types to be compared, something
// not offered by the package functions.
// CompareAndSwapPointer below only ensures vp.data
// has not changed since LoadPointer.
data := LoadPointer(&vp.data)
var i any
(*ifaceWords)(unsafe.Pointer(&i)).typ = typ
(*ifaceWords)(unsafe.Pointer(&i)).data = data
if i != old {return false}
return CompareAndSwapPointer(&vp.data, data, np.data)
}
}type
Go1.19 新增的类型，应用 ayomic 类型能够保障平安。新增了 Uintptr，反对了对范型的反对。
// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package atomic
import "unsafe"
// A Bool is an atomic boolean value.
// The zero value is false.
type Bool struct {
_ noCopy
v uint32
}
// Load atomically loads and returns the value stored in x.
func (x *Bool) Load() bool { return LoadUint32(&x.v) != 0 }
// Store atomically stores val into x.
func (x *Bool) Store(val bool) {StoreUint32(&x.v, b32(val)) }
// Swap atomically stores new into x and returns the previous value.
func (x *Bool) Swap(new bool) (old bool) {return SwapUint32(&x.v, b32(new)) != 0 }
// CompareAndSwap executes the compare-and-swap operation for the boolean value x.
func (x *Bool) CompareAndSwap(old, new bool) (swapped bool) {return CompareAndSwapUint32(&x.v, b32(old), b32(new))
}
// b32 returns a uint32 0 or 1 representing b.
func b32(b bool) uint32 {
if b {return 1}
return 0
}
// A Pointer is an atomic pointer of type *T. The zero value is a nil *T.
type Pointer[T any] struct {
_ noCopy
v unsafe.Pointer
}
// Load atomically loads and returns the value stored in x.
func (x *Pointer[T]) Load() *T { return (*T)(LoadPointer(&x.v)) }
// Store atomically stores val into x.
func (x *Pointer[T]) Store(val *T) {StorePointer(&x.v, unsafe.Pointer(val)) }
// Swap atomically stores new into x and returns the previous value.
func (x *Pointer[T]) Swap(new *T) (old *T) {return (*T)(SwapPointer(&x.v, unsafe.Pointer(new))) }
// CompareAndSwap executes the compare-and-swap operation for x.
func (x *Pointer[T]) CompareAndSwap(old, new *T) (swapped bool) {return CompareAndSwapPointer(&x.v, unsafe.Pointer(old), unsafe.Pointer(new))
}
// An Int32 is an atomic int32. The zero value is zero.
type Int32 struct {
_ noCopy
v int32
}
// Load atomically loads and returns the value stored in x.
func (x *Int32) Load() int32 { return LoadInt32(&x.v) }
// Store atomically stores val into x.
func (x *Int32) Store(val int32) {StoreInt32(&x.v, val) }
// Swap atomically stores new into x and returns the previous value.
func (x *Int32) Swap(new int32) (old int32) {return SwapInt32(&x.v, new) }
// CompareAndSwap executes the compare-and-swap operation for x.
func (x *Int32) CompareAndSwap(old, new int32) (swapped bool) {return CompareAndSwapInt32(&x.v, old, new)
}
// Add atomically adds delta to x and returns the new value.
func (x *Int32) Add(delta int32) (new int32) {return AddInt32(&x.v, delta) }
// An Int64 is an atomic int64. The zero value is zero.
type Int64 struct {
_ noCopy
_ align64
v int64
}
// Load atomically loads and returns the value stored in x.
func (x *Int64) Load() int64 { return LoadInt64(&x.v) }
// Store atomically stores val into x.
func (x *Int64) Store(val int64) {StoreInt64(&x.v, val) }
// Swap atomically stores new into x and returns the previous value.
func (x *Int64) Swap(new int64) (old int64) {return SwapInt64(&x.v, new) }
// CompareAndSwap executes the compare-and-swap operation for x.
func (x *Int64) CompareAndSwap(old, new int64) (swapped bool) {return CompareAndSwapInt64(&x.v, old, new)
}
// Add atomically adds delta to x and returns the new value.
func (x *Int64) Add(delta int64) (new int64) {return AddInt64(&x.v, delta) }
// An Uint32 is an atomic uint32. The zero value is zero.
type Uint32 struct {
_ noCopy
v uint32
}
// Load atomically loads and returns the value stored in x.
func (x *Uint32) Load() uint32 { return LoadUint32(&x.v) }
// Store atomically stores val into x.
func (x *Uint32) Store(val uint32) {StoreUint32(&x.v, val) }
// Swap atomically stores new into x and returns the previous value.
func (x *Uint32) Swap(new uint32) (old uint32) {return SwapUint32(&x.v, new) }
// CompareAndSwap executes the compare-and-swap operation for x.
func (x *Uint32) CompareAndSwap(old, new uint32) (swapped bool) {return CompareAndSwapUint32(&x.v, old, new)
}
// Add atomically adds delta to x and returns the new value.
func (x *Uint32) Add(delta uint32) (new uint32) {return AddUint32(&x.v, delta) }
// An Uint64 is an atomic uint64. The zero value is zero.
type Uint64 struct {
_ noCopy
_ align64
v uint64
}
// Load atomically loads and returns the value stored in x.
func (x *Uint64) Load() uint64 { return LoadUint64(&x.v) }
// Store atomically stores val into x.
func (x *Uint64) Store(val uint64) {StoreUint64(&x.v, val) }
// Swap atomically stores new into x and returns the previous value.
func (x *Uint64) Swap(new uint64) (old uint64) {return SwapUint64(&x.v, new) }
// CompareAndSwap executes the compare-and-swap operation for x.
func (x *Uint64) CompareAndSwap(old, new uint64) (swapped bool) {return CompareAndSwapUint64(&x.v, old, new)
}
// Add atomically adds delta to x and returns the new value.
func (x *Uint64) Add(delta uint64) (new uint64) {return AddUint64(&x.v, delta) }
// An Uintptr is an atomic uintptr. The zero value is zero.
type Uintptr struct {
_ noCopy
v uintptr
}
// Load atomically loads and returns the value stored in x.
func (x *Uintptr) Load() uintptr { return LoadUintptr(&x.v) }
// Store atomically stores val into x.
func (x *Uintptr) Store(val uintptr) {StoreUintptr(&x.v, val) }
// Swap atomically stores new into x and returns the previous value.
func (x *Uintptr) Swap(new uintptr) (old uintptr) {return SwapUintptr(&x.v, new) }
// CompareAndSwap executes the compare-and-swap operation for x.
func (x *Uintptr) CompareAndSwap(old, new uintptr) (swapped bool) {return CompareAndSwapUintptr(&x.v, old, new)
}
// Add atomically adds delta to x and returns the new value.
func (x *Uintptr) Add(delta uintptr) (new uintptr) {return AddUintptr(&x.v, delta) }
// noCopy may be added to structs which must not be copied
// after the first use.
//
// See https://golang.org/issues/8005#issuecomment-190753527
// for details.
//
// Note that it must not be embedded, due to the Lock and Unlock methods.
type noCopy struct{}
// Lock is a no-op used by -copylocks checker from `go vet`.
func (*noCopy) Lock() {}
func (*noCopy) Unlock() {}
// align64 may be added to structs that must be 64-bit aligned.
// This struct is recognized by a special case in the compiler
// and will not work if copied to any other package.
type align64 struct{}
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