From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/go/sync%2Fatomic%2Findex.html | 295 ++++++++++++++++++++++++++++++++++ 1 file changed, 295 insertions(+) create mode 100644 devdocs/go/sync%2Fatomic%2Findex.html (limited to 'devdocs/go/sync%2Fatomic%2Findex.html') diff --git a/devdocs/go/sync%2Fatomic%2Findex.html b/devdocs/go/sync%2Fatomic%2Findex.html new file mode 100644 index 00000000..f5fd3ba4 --- /dev/null +++ b/devdocs/go/sync%2Fatomic%2Findex.html @@ -0,0 +1,295 @@ +

Package atomic

Overview

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

Examples

Value (Config)
Value (ReadMostly)

Package files

doc.go type.go value.go

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 1.2 

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 1.2 

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 1.2 

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 1.2 

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 1.2 

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 1.2 

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.

+

type Bool 1.19

A Bool is an atomic boolean value. The zero value is false.

+
type Bool struct {
+    // contains filtered or unexported fields
+}
+

func (*Bool) CompareAndSwap 1.19 

func (x *Bool) CompareAndSwap(old, new bool) (swapped bool)

CompareAndSwap executes the compare-and-swap operation for the boolean value x.

+

func (*Bool) Load 1.19 

func (x *Bool) Load() bool

Load atomically loads and returns the value stored in x.

+

func (*Bool) Store 1.19 

func (x *Bool) Store(val bool)

Store atomically stores val into x.

+

func (*Bool) Swap 1.19 

func (x *Bool) Swap(new bool) (old bool)

Swap atomically stores new into x and returns the previous value.

+

type Int32 1.19

An Int32 is an atomic int32. The zero value is zero.

+
type Int32 struct {
+    // contains filtered or unexported fields
+}
+

func (*Int32) Add 1.19 

func (x *Int32) Add(delta int32) (new int32)

Add atomically adds delta to x and returns the new value.

+

func (*Int32) CompareAndSwap 1.19 

func (x *Int32) CompareAndSwap(old, new int32) (swapped bool)

CompareAndSwap executes the compare-and-swap operation for x.

+

func (*Int32) Load 1.19 

func (x *Int32) Load() int32

Load atomically loads and returns the value stored in x.

+

func (*Int32) Store 1.19 

func (x *Int32) Store(val int32)

Store atomically stores val into x.

+

func (*Int32) Swap 1.19 

func (x *Int32) Swap(new int32) (old int32)

Swap atomically stores new into x and returns the previous value.

+

type Int64 1.19

An Int64 is an atomic int64. The zero value is zero.

+
type Int64 struct {
+    // contains filtered or unexported fields
+}
+

func (*Int64) Add 1.19 

func (x *Int64) Add(delta int64) (new int64)

Add atomically adds delta to x and returns the new value.

+

func (*Int64) CompareAndSwap 1.19 

func (x *Int64) CompareAndSwap(old, new int64) (swapped bool)

CompareAndSwap executes the compare-and-swap operation for x.

+

func (*Int64) Load 1.19 

func (x *Int64) Load() int64

Load atomically loads and returns the value stored in x.

+

func (*Int64) Store 1.19 

func (x *Int64) Store(val int64)

Store atomically stores val into x.

+

func (*Int64) Swap 1.19 

func (x *Int64) Swap(new int64) (old int64)

Swap atomically stores new into x and returns the previous value.

+

type Pointer

A Pointer is an atomic pointer of type *T. The zero value is a nil *T.

+
type Pointer[T any] struct {
+    // contains filtered or unexported fields
+}
+

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 1.19

A Uint32 is an atomic uint32. The zero value is zero.

+
type Uint32 struct {
+    // contains filtered or unexported fields
+}
+

func (*Uint32) Add 1.19 

func (x *Uint32) Add(delta uint32) (new uint32)

Add atomically adds delta to x and returns the new value.

+

func (*Uint32) CompareAndSwap 1.19 

func (x *Uint32) CompareAndSwap(old, new uint32) (swapped bool)

CompareAndSwap executes the compare-and-swap operation for x.

+

func (*Uint32) Load 1.19 

func (x *Uint32) Load() uint32

Load atomically loads and returns the value stored in x.

+

func (*Uint32) Store 1.19 

func (x *Uint32) Store(val uint32)

Store atomically stores val into x.

+

func (*Uint32) Swap 1.19 

func (x *Uint32) Swap(new uint32) (old uint32)

Swap atomically stores new into x and returns the previous value.

+

type Uint64 1.19

A Uint64 is an atomic uint64. The zero value is zero.

+
type Uint64 struct {
+    // contains filtered or unexported fields
+}
+

func (*Uint64) Add 1.19 

func (x *Uint64) Add(delta uint64) (new uint64)

Add atomically adds delta to x and returns the new value.

+

func (*Uint64) CompareAndSwap 1.19 

func (x *Uint64) CompareAndSwap(old, new uint64) (swapped bool)

CompareAndSwap executes the compare-and-swap operation for x.

+

func (*Uint64) Load 1.19 

func (x *Uint64) Load() uint64

Load atomically loads and returns the value stored in x.

+

func (*Uint64) Store 1.19 

func (x *Uint64) Store(val uint64)

Store atomically stores val into x.

+

func (*Uint64) Swap 1.19 

func (x *Uint64) Swap(new uint64) (old uint64)

Swap atomically stores new into x and returns the previous value.

+

type Uintptr 1.19

A Uintptr is an atomic uintptr. The zero value is zero.

+
type Uintptr struct {
+    // contains filtered or unexported fields
+}
+

func (*Uintptr) Add 1.19 

func (x *Uintptr) Add(delta uintptr) (new uintptr)

Add atomically adds delta to x and returns the new value.

+

func (*Uintptr) CompareAndSwap 1.19 

func (x *Uintptr) CompareAndSwap(old, new uintptr) (swapped bool)

CompareAndSwap executes the compare-and-swap operation for x.

+

func (*Uintptr) Load 1.19 

func (x *Uintptr) Load() uintptr

Load atomically loads and returns the value stored in x.

+

func (*Uintptr) Store 1.19 

func (x *Uintptr) Store(val uintptr)

Store atomically stores val into x.

+

func (*Uintptr) Swap 1.19 

func (x *Uintptr) Swap(new uintptr) (old uintptr)

Swap atomically stores new into x and returns the previous value.

+

type Value 1.4

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.

+
type Value struct {
+    // contains filtered or unexported fields
+}
+

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 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:

+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 1.17 

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 1.4 

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 1.4 

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 1.17 

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

+

+ © Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
+ http://golang.org/pkg/sync/atomic/ +

+
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