package atomic
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.
Index ¶
- func AddInt32(addr *int32, delta int32) (new int32)
- func AddInt64(addr *int64, delta int64) (new int64)
- func AddUint32(addr *uint32, delta uint32) (new uint32)
- func AddUint64(addr *uint64, delta uint64) (new uint64)
- func AddUintptr(addr *uintptr, delta uintptr) (new uintptr)
- func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool)
- func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool)
- func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool)
- func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool)
- func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool)
- func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool)
- func LoadInt32(addr *int32) (val int32)
- func LoadInt64(addr *int64) (val int64)
- func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer)
- func LoadUint32(addr *uint32) (val uint32)
- func LoadUint64(addr *uint64) (val uint64)
- func LoadUintptr(addr *uintptr) (val uintptr)
- func StoreInt32(addr *int32, val int32)
- func StoreInt64(addr *int64, val int64)
- func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer)
- func StoreUint32(addr *uint32, val uint32)
- func StoreUint64(addr *uint64, val uint64)
- func StoreUintptr(addr *uintptr, val uintptr)
- func SwapInt32(addr *int32, new int32) (old int32)
- func SwapInt64(addr *int64, new int64) (old int64)
- func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer)
- func SwapUint32(addr *uint32, new uint32) (old uint32)
- func SwapUint64(addr *uint64, new uint64) (old uint64)
- func SwapUintptr(addr *uintptr, new uintptr) (old uintptr)
- type Bool
- func (x *Bool) CompareAndSwap(old, new bool) (swapped bool)
- func (x *Bool) Load() bool
- func (x *Bool) Store(val bool)
- func (x *Bool) Swap(new bool) (old bool)
- type Int32
- func (x *Int32) Add(delta int32) (new int32)
- func (x *Int32) CompareAndSwap(old, new int32) (swapped bool)
- func (x *Int32) Load() int32
- func (x *Int32) Store(val int32)
- func (x *Int32) Swap(new int32) (old int32)
- type Int64
- func (x *Int64) Add(delta int64) (new int64)
- func (x *Int64) CompareAndSwap(old, new int64) (swapped bool)
- func (x *Int64) Load() int64
- func (x *Int64) Store(val int64)
- func (x *Int64) Swap(new int64) (old int64)
- type Pointer
- func (x *Pointer[T]) CompareAndSwap(old, new *T) (swapped bool)
- func (x *Pointer[T]) Load() *T
- func (x *Pointer[T]) Store(val *T)
- func (x *Pointer[T]) Swap(new *T) (old *T)
- type Uint32
- func (x *Uint32) Add(delta uint32) (new uint32)
- func (x *Uint32) CompareAndSwap(old, new uint32) (swapped bool)
- func (x *Uint32) Load() uint32
- func (x *Uint32) Store(val uint32)
- func (x *Uint32) Swap(new uint32) (old uint32)
- type Uint64
- func (x *Uint64) Add(delta uint64) (new uint64)
- func (x *Uint64) CompareAndSwap(old, new uint64) (swapped bool)
- func (x *Uint64) Load() uint64
- func (x *Uint64) Store(val uint64)
- func (x *Uint64) Swap(new uint64) (old uint64)
- type Uintptr
- func (x *Uintptr) Add(delta uintptr) (new uintptr)
- func (x *Uintptr) CompareAndSwap(old, new uintptr) (swapped bool)
- func (x *Uintptr) Load() uintptr
- func (x *Uintptr) Store(val uintptr)
- func (x *Uintptr) Swap(new uintptr) (old uintptr)
- type Value
- func (v *Value) CompareAndSwap(old, new any) (swapped bool)
- func (v *Value) Load() (val any)
- func (v *Value) Store(val any)
- func (v *Value) Swap(new any) (old any)
- Bugs
Examples ¶
Functions ¶
func AddInt32 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
LoadInt32 atomically loads *addr. Consider using the more ergonomic and less error-prone Int32.Load instead.
func LoadInt64 ¶
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 ¶
LoadPointer atomically loads *addr. Consider using the more ergonomic and less error-prone Pointer.Load instead.
func LoadUint32 ¶
LoadUint32 atomically loads *addr. Consider using the more ergonomic and less error-prone Uint32.Load instead.
func LoadUint64 ¶
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 ¶
LoadUintptr atomically loads *addr. Consider using the more ergonomic and less error-prone Uintptr.Load instead.
func StoreInt32 ¶
StoreInt32 atomically stores val into *addr. Consider using the more ergonomic and less error-prone Int32.Store instead.
func StoreInt64 ¶
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 ¶
StorePointer atomically stores val into *addr. Consider using the more ergonomic and less error-prone Pointer.Store instead.
func StoreUint32 ¶
StoreUint32 atomically stores val into *addr. Consider using the more ergonomic and less error-prone Uint32.Store instead.
func StoreUint64 ¶
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 ¶
StoreUintptr atomically stores val into *addr. Consider using the more ergonomic and less error-prone Uintptr.Store instead.
func SwapInt32 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
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 ¶
CompareAndSwap executes the compare-and-swap operation for the boolean value x.
func (*Bool) Load ¶
Load atomically loads and returns the value stored in x.
func (*Bool) Store ¶
Store atomically stores val into x.
func (*Bool) Swap ¶
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 ¶
Add atomically adds delta to x and returns the new value.
func (*Int32) CompareAndSwap ¶
CompareAndSwap executes the compare-and-swap operation for x.
func (*Int32) Load ¶
Load atomically loads and returns the value stored in x.
func (*Int32) Store ¶
Store atomically stores val into x.
func (*Int32) Swap ¶
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 ¶
Add atomically adds delta to x and returns the new value.
func (*Int64) CompareAndSwap ¶
CompareAndSwap executes the compare-and-swap operation for x.
func (*Int64) Load ¶
Load atomically loads and returns the value stored in x.
func (*Int64) Store ¶
Store atomically stores val into x.
func (*Int64) Swap ¶
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 ¶
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 ¶
Add atomically adds delta to x and returns the new value.
func (*Uint32) CompareAndSwap ¶
CompareAndSwap executes the compare-and-swap operation for x.
func (*Uint32) Load ¶
Load atomically loads and returns the value stored in x.
func (*Uint32) Store ¶
Store atomically stores val into x.
func (*Uint32) Swap ¶
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 ¶
Add atomically adds delta to x and returns the new value.
func (*Uint64) CompareAndSwap ¶
CompareAndSwap executes the compare-and-swap operation for x.
func (*Uint64) Load ¶
Load atomically loads and returns the value stored in x.
func (*Uint64) Store ¶
Store atomically stores val into x.
func (*Uint64) Swap ¶
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 ¶
Add atomically adds delta to x and returns the new value.
func (*Uintptr) CompareAndSwap ¶
CompareAndSwap executes the compare-and-swap operation for x.
func (*Uintptr) Load ¶
Load atomically loads and returns the value stored in x.
func (*Uintptr) Store ¶
Store atomically stores val into x.
func (*Uintptr) Swap ¶
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:play
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:play
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 ¶
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 ¶
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 ¶
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 ¶
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.
Source Files ¶
- Version
- v1.21.8
- Published
- Feb 29, 2024
- Platform
- js/wasm
- Imports
- 1 packages
- Last checked
- 3 minutes ago –
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