Go 协程

概述

goroutine 可能切换的点

• 非强占式

• I/O ,select

• channel

• 等待锁

• 调用函数

• runtime.Gosched()

• 只是参考，不能保证切换

代码channel

package main
 
import (
	"fmt"
	"time"
)
 
func worker(id int, c chan int) {
	for n := range c {
		fmt.Printf("Worker %d received %c\n",
			id, n)
	}
}
 
func createWorker(id int) chan<- int {
	c := make(chan int)
	go worker(id, c)
	return c
}
 
func chanDemo() {
	var channels [10]chan<- int
	for i := 0; i < 10; i++ {
		channels[i] = createWorker(i)
	}
 
	for i := 0; i < 10; i++ {
		channels[i] <- 'a' + i
	}
 
	for i := 0; i < 10; i++ {
		channels[i] <- 'A' + i
	}
 
	time.Sleep(time.Millisecond)
}
 
func bufferedChannel() {
	c := make(chan int, 3)
	go worker(0, c)
	c <- 'a'
	c <- 'b'
	c <- 'c'
	c <- 'd'
	time.Sleep(time.Millisecond)
}
 
func channelClose() {
	c := make(chan int)
	go worker(0, c)
	c <- 'a'
	c <- 'b'
	c <- 'c'
	c <- 'd'
	close(c)
	time.Sleep(time.Millisecond)
}
 
func main() {
	fmt.Println("Channel as first-class citizen")
	chanDemo()
	fmt.Println("Buffered channel")
	bufferedChannel()
	fmt.Println("Channel close and range")
	channelClose()
}

select 代码

package main
 
import (
	"fmt"
	"math/rand"
	"time"
)
 
func generator() chan int {
	out := make(chan int)
	go func() {
		i := 0
		for {
			time.Sleep(
				time.Duration(rand.Intn(1500)) *
					time.Millisecond)
			out <- i
			i++
		}
	}()
	return out
}
 
func worker(id int, c chan int) {
	for n := range c {
		time.Sleep(time.Second)
		fmt.Printf("Worker %d received %d\n",
			id, n)
	}
}
 
func createWorker(id int) chan<- int {
	c := make(chan int)
	go worker(id, c)
	return c
}
 
func main() {
	var c1, c2 = generator(), generator()
	var worker = createWorker(0)
 
	var values []int
	tm := time.After(10 * time.Second)
	tick := time.Tick(time.Second)
	for {
		var activeWorker chan<- int
		var activeValue int
		if len(values) > 0 {
			activeWorker = worker
			activeValue = values[0]
		}
 
		select {
		case n := <-c1:
			values = append(values, n)
		case n := <-c2:
			values = append(values, n)
		case activeWorker <- activeValue:
			values = values[1:]
 
		case <-time.After(800 * time.Millisecond):
			fmt.Println("timeout")
		case <-tick:
			fmt.Println(
				"queue len =", len(values))
		case <-tm:
			fmt.Println("bye")
			return
		}
	}
}

done代码

package main
 
import (
	"fmt"
	"sync"
)
 
func doWork(id int,
	w worker) {
	for n := range w.in {
		fmt.Printf("Worker %d received %c\n",
			id, n)
		w.done()
	}
}
 
type worker struct {
	in   chan int
	done func()
}
 
func createWorker(
	id int, wg *sync.WaitGroup) worker {
	w := worker{
		in: make(chan int),
		done: func() {
			wg.Done()
		},
	}
	go doWork(id, w)
	return w
}
 
func chanDemo() {
	var wg sync.WaitGroup
 
	var workers [10]worker
	for i := 0; i < 10; i++ {
		workers[i] = createWorker(i, &wg)
	}
 
	wg.Add(20)
	for i, worker := range workers {
		worker.in <- 'a' + i
	}
	for i, worker := range workers {
		worker.in <- 'A' + i
	}
 
	wg.Wait()
}
 
func main() {
	chanDemo()
}

参考：

https://www.yuque.com/docs/share/347f3ea8-794b-48c2-a2cf-0bb776ca0cbb