为什么我的代码会死锁以及如何解决它

Question

Why does my code deadlock (followed by crash) on read from channel, I would expect it to block on read after the channel is read completely, but not crash. I understand it is a deadlock state as no one is writing to the channel and read blocks on it.

How can I change the code to read all the channel content and then exit from main instead of crash.

Go playground: https://play.golang.org/p/rjXZZOx1FFZ

package main

import (
    "fmt"
    "sync"
)

func main() {
    var wg sync.WaitGroup
    news := make(chan int, 10)

    wg.Add(1)

    go foo(&wg, news) 

    wg.Wait()   

    for {
        fmt.Printf("reading: %v
", <-news) 
        //crashes here after printing 0-9
    }

}

func foo(wg *sync.WaitGroup, news chan int) {
    for i:=0; i<10;i++ {
        fmt.Printf("Writing
")
        news <- i
    }
    (*wg).Done()
}

Answer 1

The program deadlocks because main blocks on channel receive and there are no other goroutines that will send to that channel.

Use this approach to read all the channel content and then exit from main: main reads the channel until closed; foo writes all values and closes the channel.

func main() {
    news := make(chan int, 10)
    go foo(news)
    // range breaks when the channel is closed
    for v := range news { 

        fmt.Printf("reading: %v
", v)
    }

}

func foo(news chan int) {
    for i := 0; i < 10; i++ {
        fmt.Printf("Writing
")
        news <- i
    }
    // close channel to indicate that no more values will be sent.
    close(news) 
}

Run it on the Playground.