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".
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 Value
- Bugs
Examples ¶
Functions ¶
func AddInt32 ¶
AddInt32 atomically adds delta to *addr and returns the new value.
func AddInt64 ¶
AddInt64 atomically adds delta to *addr and returns the new value.
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)).
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)).
func AddUintptr ¶
AddUintptr atomically adds delta to *addr and returns the new value.
func CompareAndSwapInt32 ¶
CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value.
func CompareAndSwapInt64 ¶
CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value.
func CompareAndSwapPointer ¶
CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value.
func CompareAndSwapUint32 ¶
CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value.
func CompareAndSwapUint64 ¶
CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value.
func CompareAndSwapUintptr ¶
CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value.
func LoadInt32 ¶
LoadInt32 atomically loads *addr.
func LoadInt64 ¶
LoadInt64 atomically loads *addr.
func LoadPointer ¶
LoadPointer atomically loads *addr.
func LoadUint32 ¶
LoadUint32 atomically loads *addr.
func LoadUint64 ¶
LoadUint64 atomically loads *addr.
func LoadUintptr ¶
LoadUintptr atomically loads *addr.
func StoreInt32 ¶
StoreInt32 atomically stores val into *addr.
func StoreInt64 ¶
StoreInt64 atomically stores val into *addr.
func StorePointer ¶
StorePointer atomically stores val into *addr.
func StoreUint32 ¶
StoreUint32 atomically stores val into *addr.
func StoreUint64 ¶
StoreUint64 atomically stores val into *addr.
func StoreUintptr ¶
StoreUintptr atomically stores val into *addr.
func SwapInt32 ¶
SwapInt32 atomically stores new into *addr and returns the previous *addr value.
func SwapInt64 ¶
SwapInt64 atomically stores new into *addr and returns the previous *addr value.
func SwapPointer ¶
SwapPointer atomically stores new into *addr and returns the previous *addr value.
func SwapUint32 ¶
SwapUint32 atomically stores new into *addr and returns the previous *addr value.
func SwapUint64 ¶
SwapUint64 atomically stores new into *addr and returns the previous *addr value.
func SwapUintptr ¶
SwapUintptr atomically stores new into *addr and returns the previous *addr value.
Types ¶
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:
{
var config 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:
{
type Map map[string]string
var m 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) Load ¶
func (v *Value) Load() (x interface{})
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(x interface{})
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).
Bugs ¶
☞ On x86-32, 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 both ARM and x86-32, it is the caller's responsibility to arrange for 64-bit alignment of 64-bit words accessed atomically. The first word in a global variable or in an allocated struct or slice can be relied upon to be 64-bit aligned.
Source Files ¶
- Version
- v1.9.0-beta.1
- Published
- Jun 14, 2017
- Platform
- linux/amd64
- Imports
- 1 packages
- Last checked
- 47 seconds ago –
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