go chan deadlock

package main

import (
	"fmt"
)

func main() {

	done := make(chan struct{}, 4)
	exit := make(chan struct{})

	go func () {
		//defer close exit 依然会deadlock
		//done 通道只有1次write，有2次read
		//done 则在exit close前先产生deadlock
		defer close(exit)
		fmt.Println("Goroutine start.")
		fmt.Println("len cap",len(done), cap(done))
		d, ok := <-done
		if !ok {
			fmt.Println("done closed")
		} else {
			fmt.Println("done not closed", d, done)
		}
		//此处close 则当前goroutine立即停止执行
		//因为done 在主goroutine 有 1次write 1次read，main底部的exit不再阻塞
		//主 goroutine 提前退出
		//close(exit)
		_, ok = <-done
		if !ok {
			fmt.Println("done closed 1")
		}

		fmt.Println("Goroutine emptyChan finished")
	}()

	done <- struct{}{}

	<-exit
	fmt.Println("main done")
}


func closeNoDeadLock() {


	done := make(chan struct{})
	c := make(chan int)

	go func () {
		defer close(done)
		fmt.Println("goroutine start")
		for {
			select{
			case v, ok := <-c:
				if !ok {
					fmt.Println("c closed", v,ok)
					return
				}

				fmt.Println("c not closed", v,ok)
			}
		}

		fmt.Println("goroutine emptyChan finished")
	}()
	c <- 11
	close(c)
	<-done
	fmt.Println("main done")
}