proper way of waiting for a go routine to finish

问题

I wish to know what is the proper way of waiting for a go routine to finish before exiting the program. Reading some other answers it seems that a bool chan will do the trick, as in Playground link

func do_stuff(done chan bool) {
    fmt.Println("Doing stuff")
    done <- true
}

func main() {
    fmt.Println("Main")
    done := make(chan bool)
    go do_stuff(done)
    <-done
    //<-done
}

I have two questions here:

why the <- done works at all?
what happens if I uncomment the last line? I have a deadlock error. Is this because the channel is empty and there is no other function sending values to it?

回答1:

Why the <- done works at all?

It works because the runtime detects that you're writing something to the channel somewhere else.

what happens if I uncomment the last line?

The runtime is smart enough to know that there's nothing else being written and it deadlocks.

Bonus, if you're extremely limited on memory, you can use done := make(chan struct{}) and done <- struct{}{}, struct{} is guaranteed to use 0 memory.

回答2:

Listening to channel <- done, is a blocking operation, so your program won't continue until true or false is sent i.e. done <- true.

Your question can have a few different answers depending on the circumstance.

For instance, suppose you wanted to parallelize a series of function calls that take a long time.

I would use the sync package for this

package main

import (
    "fmt"
    "sync"
    "time"
)

func main() {
    var wg sync.WaitGroup
    for i := 0; i < 10; i++ {
        wg.Add(1)
        go func() {
            longOp()
            wg.Done()
        }()
    }
    // will wait until wg.Done is called 10 times
    // since we made wg.Add(1) call 10 times
    wg.Wait()
}

func longOp() {
    time.Sleep(time.Second * 2)
    fmt.Println("long op done")
}

来源：https://stackoverflow.com/questions/25954481/proper-way-of-waiting-for-a-go-routine-to-finish

标签

channel

goroutine