# package atomic - sync/atomic - godocs.io

```
import "sync/atomic"
```

Package atomic provides low-level atomic memory primitives useful for implementing synchronization algorithms.

These functions require great care to be used correctly. Except for special, low-level applications, synchronization is better done with channels or the facilities of the sync package. Share memory by communicating; don't communicate by sharing memory.

The swap operation, implemented by the SwapT functions, is the atomic equivalent of:

```
old = *addr
*addr = new
return old
```

The compare-and-swap operation, implemented by the CompareAndSwapT functions, is the atomic equivalent of:

```
if *addr == old {
	*addr = new
	return true
}
return false
```

The add operation, implemented by the AddT functions, is the atomic equivalent of:

```
*addr += delta
return *addr
```

The load and store operations, implemented by the LoadT and StoreT functions, are the atomic equivalents of "return *addr" and "*addr = val".

In the terminology of the Go memory model, if the effect of an atomic operation A is observed by atomic operation B, then A “synchronizes before” B. Additionally, all the atomic operations executed in a program behave as though executed in some sequentially consistent order. This definition provides the same semantics as C++'s sequentially consistent atomics and Java's volatile variables.

## Functions

### func AddInt32
```
func AddInt32(addr *int32, delta int32) (new int32)
```
AddInt32 atomically adds delta to *addr and returns the new value. Consider using the more ergonomic and less error-prone Int32.Add instead.

### func AddInt64
```
func AddInt64(addr *int64, delta int64) (new int64)
```
AddInt64 atomically adds delta to *addr and returns the new value. Consider using the more ergonomic and less error-prone Int64.Add instead (particularly if you target 32-bit platforms; see the bugs section).

### func AddUint32
```
func AddUint32(addr *uint32, delta uint32) (new uint32)
```
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)). Consider using the more ergonomic and less error-prone Uint32.Add instead.

### func AddUint64
```
func AddUint64(addr *uint64, delta uint64) (new uint64)
```
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)). Consider using the more ergonomic and less error-prone Uint64.Add instead (particularly if you target 32-bit platforms; see the bugs section).

### func AddUintptr
```
func AddUintptr(addr *uintptr, delta uintptr) (new uintptr)
```
AddUintptr atomically adds delta to *addr and returns the new value. Consider using the more ergonomic and less error-prone Uintptr.Add instead.

### func CompareAndSwapInt32
```
func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool)
```
CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value. Consider using the more ergonomic and less error-prone Int32.CompareAndSwap instead.

### func CompareAndSwapInt64
```
func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool)
```
CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value. Consider using the more ergonomic and less error-prone Int64.CompareAndSwap instead (particularly if you target 32-bit platforms; see the bugs section).

### func CompareAndSwapPointer
```
func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool)
```
CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value. Consider using the more ergonomic and less error-prone Pointer.CompareAndSwap instead.

### func CompareAndSwapUint32
```
func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool)
```
CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value. Consider using the more ergonomic and less error-prone Uint32.CompareAndSwap instead.

### func CompareAndSwapUint64
```
func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool)
```
CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value. Consider using the more ergonomic and less error-prone Uint64.CompareAndSwap instead (particularly if you target 32-bit platforms; see the bugs section).

### func CompareAndSwapUintptr
```
func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool)
```
CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value. Consider using the more ergonomic and less error-prone Uintptr.CompareAndSwap instead.

### func LoadInt32
```
func LoadInt32(addr *int32) (val int32)
```
LoadInt32 atomically loads *addr. Consider using the more ergonomic and less error-prone Int32.Load instead.

### func LoadInt64
```
func LoadInt64(addr *int64) (val int64)
```
LoadInt64 atomically loads *addr. Consider using the more ergonomic and less error-prone Int64.Load instead (particularly if you target 32-bit platforms; see the bugs section).

### func LoadPointer
```
func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer)
```
LoadPointer atomically loads *addr. Consider using the more ergonomic and less error-prone Pointer.Load instead.

### func LoadUint32
```
func LoadUint32(addr *uint32) (val uint32)
```
LoadUint32 atomically loads *addr. Consider using the more ergonomic and less error-prone Uint32.Load instead.

### func LoadUint64
```
func LoadUint64(addr *uint64) (val uint64)
```
LoadUint64 atomically loads *addr. Consider using the more ergonomic and less error-prone Uint64.Load instead (particularly if you target 32-bit platforms; see the bugs section).

### func LoadUintptr
```
func LoadUintptr(addr *uintptr) (val uintptr)
```
LoadUintptr atomically loads *addr. Consider using the more ergonomic and less error-prone Uintptr.Load instead.

### func StoreInt32
```
func StoreInt32(addr *int32, val int32)
```
StoreInt32 atomically stores val into *addr. Consider using the more ergonomic and less error-prone Int32.Store instead.

### func StoreInt64
```
func StoreInt64(addr *int64, val int64)
```
StoreInt64 atomically stores val into *addr. Consider using the more ergonomic and less error-prone Int64.Store instead (particularly if you target 32-bit platforms; see the bugs section).

### func StorePointer
```
func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer)
```
StorePointer atomically stores val into *addr. Consider using the more ergonomic and less error-prone Pointer.Store instead.

### func StoreUint32
```
func StoreUint32(addr *uint32, val uint32)
```
StoreUint32 atomically stores val into *addr. Consider using the more ergonomic and less error-prone Uint32.Store instead.

### func StoreUint64
```
func StoreUint64(addr *uint64, val uint64)
```
StoreUint64 atomically stores val into *addr. Consider using the more ergonomic and less error-prone Uint64.Store instead (particularly if you target 32-bit platforms; see the bugs section).

### func StoreUintptr
```
func StoreUintptr(addr *uintptr, val uintptr)
```
StoreUintptr atomically stores val into *addr. Consider using the more ergonomic and less error-prone Uintptr.Store instead.

### func SwapInt32
```
func SwapInt32(addr *int32, new int32) (old int32)
```
SwapInt32 atomically stores new into *addr and returns the previous *addr value. Consider using the more ergonomic and less error-prone Int32.Swap instead.

### func SwapInt64
```
func SwapInt64(addr *int64, new int64) (old int64)
```
SwapInt64 atomically stores new into *addr and returns the previous *addr value. Consider using the more ergonomic and less error-prone Int64.Swap instead (particularly if you target 32-bit platforms; see the bugs section).

### func SwapPointer
```
func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer)
```
SwapPointer atomically stores new into *addr and returns the previous *addr value. Consider using the more ergonomic and less error-prone Pointer.Swap instead.

### func SwapUint32
```
func SwapUint32(addr *uint32, new uint32) (old uint32)
```
SwapUint32 atomically stores new into *addr and returns the previous *addr value. Consider using the more ergonomic and less error-prone Uint32.Swap instead.

### func SwapUint64
```
func SwapUint64(addr *uint64, new uint64) (old uint64)
```
SwapUint64 atomically stores new into *addr and returns the previous *addr value. Consider using the more ergonomic and less error-prone Uint64.Swap instead (particularly if you target 32-bit platforms; see the bugs section).

### func SwapUintptr
```
func SwapUintptr(addr *uintptr, new uintptr) (old uintptr)
```
SwapUintptr atomically stores new into *addr and returns the previous *addr value. Consider using the more ergonomic and less error-prone Uintptr.Swap instead.

## Types

### type Bool
```
type Bool struct {
	// contains filtered or unexported fields
}
```
A Bool is an atomic boolean value. The zero value is false.

### func (*Bool) CompareAndSwap
```
func (x *Bool) CompareAndSwap(old, new bool) (swapped bool)
```
CompareAndSwap executes the compare-and-swap operation for the boolean value x.

### func (*Bool) Load
```
func (x *Bool) Load() bool
```
Load atomically loads and returns the value stored in x.

### func (*Bool) Store
```
func (x *Bool) Store(val bool)
```
Store atomically stores val into x.

### func (*Bool) Swap
```
func (x *Bool) Swap(new bool) (old bool)
```
Swap atomically stores new into x and returns the previous value.

### type Int32
```
type Int32 struct {
	// contains filtered or unexported fields
}
```
An Int32 is an atomic int32. The zero value is zero.

### func (*Int32) Add
```
func (x *Int32) Add(delta int32) (new int32)
```
Add atomically adds delta to x and returns the new value.

### func (*Int32) CompareAndSwap
```
func (x *Int32) CompareAndSwap(old, new int32) (swapped bool)
```
CompareAndSwap executes the compare-and-swap operation for x.

### func (*Int32) Load
```
func (x *Int32) Load() int32
```
Load atomically loads and returns the value stored in x.

### func (*Int32) Store
```
func (x *Int32) Store(val int32)
```
Store atomically stores val into x.

### func (*Int32) Swap
```
func (x *Int32) Swap(new int32) (old int32)
```
Swap atomically stores new into x and returns the previous value.

### type Int64
```
type Int64 struct {
	// contains filtered or unexported fields
}
```
An Int64 is an atomic int64. The zero value is zero.

### func (*Int64) Add
```
func (x *Int64) Add(delta int64) (new int64)
```
Add atomically adds delta to x and returns the new value.

### func (*Int64) CompareAndSwap
```
func (x *Int64) CompareAndSwap(old, new int64) (swapped bool)
```
CompareAndSwap executes the compare-and-swap operation for x.

### func (*Int64) Load
```
func (x *Int64) Load() int64
```
Load atomically loads and returns the value stored in x.

### func (*Int64) Store
```
func (x *Int64) Store(val int64)
```
Store atomically stores val into x.

### func (*Int64) Swap
```
func (x *Int64) Swap(new int64) (old int64)
```
Swap atomically stores new into x and returns the previous value.

### type Pointer
```
type Pointer[T any] struct {
	// contains filtered or unexported fields
}
```
A Pointer is an atomic pointer of type *T. The zero value is a nil *T.

### func (*Pointer[T]) CompareAndSwap
```
func (x *Pointer[T]) CompareAndSwap(old, new *T) (swapped bool)
```
CompareAndSwap executes the compare-and-swap operation for x.

### func (*Pointer[T]) Load
```
func (x *Pointer[T]) Load() *T
```
Load atomically loads and returns the value stored in x.

### func (*Pointer[T]) Store
```
func (x *Pointer[T]) Store(val *T)
```
Store atomically stores val into x.

### func (*Pointer[T]) Swap
```
func (x *Pointer[T]) Swap(new *T) (old *T)
```
Swap atomically stores new into x and returns the previous value.

### type Uint32
```
type Uint32 struct {
	// contains filtered or unexported fields
}
```
A Uint32 is an atomic uint32. The zero value is zero.

### func (*Uint32) Add
```
func (x *Uint32) Add(delta uint32) (new uint32)
```
Add atomically adds delta to x and returns the new value.

### func (*Uint32) CompareAndSwap
```
func (x *Uint32) CompareAndSwap(old, new uint32) (swapped bool)
```
CompareAndSwap executes the compare-and-swap operation for x.

### func (*Uint32) Load
```
func (x *Uint32) Load() uint32
```
Load atomically loads and returns the value stored in x.

### func (*Uint32) Store
```
func (x *Uint32) Store(val uint32)
```
Store atomically stores val into x.

### func (*Uint32) Swap
```
func (x *Uint32) Swap(new uint32) (old uint32)
```
Swap atomically stores new into x and returns the previous value.

### type Uint64
```
type Uint64 struct {
	// contains filtered or unexported fields
}
```
A Uint64 is an atomic uint64. The zero value is zero.

### func (*Uint64) Add
```
func (x *Uint64) Add(delta uint64) (new uint64)
```
Add atomically adds delta to x and returns the new value.

### func (*Uint64) CompareAndSwap
```
func (x *Uint64) CompareAndSwap(old, new uint64) (swapped bool)
```
CompareAndSwap executes the compare-and-swap operation for x.

### func (*Uint64) Load
```
func (x *Uint64) Load() uint64
```
Load atomically loads and returns the value stored in x.

### func (*Uint64) Store
```
func (x *Uint64) Store(val uint64)
```
Store atomically stores val into x.

### func (*Uint64) Swap
```
func (x *Uint64) Swap(new uint64) (old uint64)
```
Swap atomically stores new into x and returns the previous value.

### type Uintptr
```
type Uintptr struct {
	// contains filtered or unexported fields
}
```
A Uintptr is an atomic uintptr. The zero value is zero.

### func (*Uintptr) Add
```
func (x *Uintptr) Add(delta uintptr) (new uintptr)
```
Add atomically adds delta to x and returns the new value.

### func (*Uintptr) CompareAndSwap
```
func (x *Uintptr) CompareAndSwap(old, new uintptr) (swapped bool)
```
CompareAndSwap executes the compare-and-swap operation for x.

### func (*Uintptr) Load
```
func (x *Uintptr) Load() uintptr
```
Load atomically loads and returns the value stored in x.

### func (*Uintptr) Store
```
func (x *Uintptr) Store(val uintptr)
```
Store atomically stores val into x.

### func (*Uintptr) Swap
```
func (x *Uintptr) Swap(new uintptr) (old uintptr)
```
Swap atomically stores new into x and returns the previous value.

### type Value
```
type Value struct {
	// contains filtered or unexported fields
}
```
A Value provides an atomic load and store of a consistently typed value. The zero value for a Value returns nil from Load. Once Store has been called, a Value must not be copied.

A Value must not be copied after first use.

### Example (Config)

The following example shows how to use Value for periodic program config updates and propagation of the changes to worker goroutines.

Code:
```
package main

import (
	"sync/atomic"
	"time"
)

func loadConfig() map[string]string {
	return make(map[string]string)
}

func requests() chan int {
	return make(chan int)
}

func main() {
	var config atomic.Value // holds current server configuration
	// Create initial config value and store into config.
	config.Store(loadConfig())
	go func() {
		// Reload config every 10 seconds
		// and update config value with the new version.
		for {
			time.Sleep(10 * time.Second)
			config.Store(loadConfig())
		}
	}()
	// Create worker goroutines that handle incoming requests
	// using the latest config value.
	for i := 0; i < 10; i++ {
		go func() {
			for r := range requests() {
				c := config.Load()
				// Handle request r using config c.
				_, _ = r, c
			}
		}()
	}
}

```

### Example (ReadMostly)

The following example shows how to maintain a scalable frequently read, but infrequently updated data structure using copy-on-write idiom.

Code:
```
package main

import (
	"sync"
	"sync/atomic"
)

func main() {
	type Map map[string]string
	var m atomic.Value
	m.Store(make(Map))
	var mu sync.Mutex // used only by writers
	// read function can be used to read the data without further synchronization
	read := func(key string) (val string) {
		m1 := m.Load().(Map)
		return m1[key]
	}
	// insert function can be used to update the data without further synchronization
	insert := func(key, val string) {
		mu.Lock() // synchronize with other potential writers
		defer mu.Unlock()
		m1 := m.Load().(Map) // load current value of the data structure
		m2 := make(Map)      // create a new value
		for k, v := range m1 {
			m2[k] = v // copy all data from the current object to the new one
		}
		m2[key] = val // do the update that we need
		m.Store(m2)   // atomically replace the current object with the new one
		// At this point all new readers start working with the new version.
		// The old version will be garbage collected once the existing readers
		// (if any) are done with it.
	}
	_, _ = read, insert
}

```

### func (*Value) CompareAndSwap
```
func (v *Value) CompareAndSwap(old, new any) (swapped bool)
```
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 (*Value) Load
```
func (v *Value) Load() (val any)
```
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 (*Value) Store
```
func (v *Value) Store(val any)
```
Store sets the value of the Value v to val. 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 (*Value) Swap
```
func (v *Value) Swap(new any) (old any)
```
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).

## Bugs

* On 386, the 64-bit functions use instructions unavailable before the Pentium MMX.

On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core.

On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
for 64-bit alignment of 64-bit words accessed atomically via the primitive
atomic functions (types [Int64] and [Uint64] are automatically aligned).
The first word in an allocated struct, array, or slice; in a global
variable; or in a local variable (because the subject of all atomic operations
will escape to the heap) can be relied upon to be 64-bit aligned.


## Details
=> ?view=versions Version: v1.22.5 (latest)
* Published: Jun 27, 2024
=> ?view=platforms Platform: linux/amd64
=> ?view=imports Imports: 1 packages
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