• 版本
  golang -- 1.12.4

• golang协程同步

1.channel - monitor goroutine

var deposits = make(chan int) // send amount to deposit
var balances = make(chan int) // receive balance

func Deposit(amount int) { deposits <- amount }
func Balance() int       { return <-balances }

func teller() {
     var balance int // balance is confined to teller goroutine
     for {
         select {
         case amount := <-deposits:
              balance += amount
         case balances <- balance:
         }
      }
}
func init() {
     go teller() // start the monitor goroutine
}

2.channel - serial confinement

type Cake struct{ state string }

func baker(cooked chan<- *Cake) {
     for {
             cake := new(Cake)
             cake.state = "cooked"
             cooked <- cake // baker never touches this cake again
         } 
}

func icer(iced chan<- *Cake, cooked <-chan *Cake) {
      for cake := range cooked {
             cake.state = "iced"
             iced <- cake // icer never touches this cake again
      } 
}

3.mutual exclusion

import "sync"

var mu      sync.Mutex // guards balance
var balance int

func Deposit(amount int) {
         mu.Lock()
         balance = balance + amount
         mu.Unlock()
}

func Balance() int {
         mu.Lock()
         defer mu.Unlock()
         return balance
}

4.mutual exclusion - RWMutex

import "sync"

var mu      sync.RWMutex // guards balance
var balance int

func Deposit(amount int) {
         mu.Lock()
         balance = balance + amount
         mu.Unlock()
}

func Balance() int {
         mu.RLock() //readers lock
         defer mu.RUnlock()
         return balance
}

RLock允许读取并行，写入和读取完全互斥，多次读取，一次写入

5.Lazy Initialization - sync.Once

var loadIconsOnce sync.Once
var icons map[string]image.Image
// Concurrency-safe.
func Icon(name string) image.Image {
     loadIconsOnce.Do(loadIcons)
     return icons[name]
}