长时间运行的 go 例程完成时发出信号

Question

In this code I have a loop that will run until a certain amount of time has passed. During this time I send a random amount of numbers to a channel to be processed by a longer running go routine. The problem is the go routines still need to finish doing some kind of task (just sleeping in this example). How do I make sure all of the items sent to the numbers channel are completed running and all of the items sent to the messages channel are read?

When I run the code I see 66 numbers should have run and been read. But the output only shows 6 out of 66 were run and then read out.

0s
10ms
20ms
30ms
40ms
50ms
60ms
70ms
80ms
90ms
Ran 3
Ran 5
Ran 1
Ran 0
100ms
Ran 4
Ran 2
110ms
DONE 66

Go Playground

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func DoStuff(n int, messages chan string) {
    time.Sleep(time.Duration(100) * time.Millisecond)
    messages <- fmt.Sprintf("Ran %d", n)
}

func Read(messages chan string) {
    for m := range messages {
        fmt.Println(m)
    }
}

func Run(numbers chan int, messages chan string) {
    for n := range numbers {
            go DoStuff(n, messages)
        }   
}

func main() {
    var min = 1
    var max = 10

    var numbers = make(chan int)
    var messages = make(chan string)

    go Read(messages)
    go Run(numbers, messages)

    var n = 0
    for start := time.Now(); ; {
        elapsedTime := time.Since(start)
        fmt.Println(elapsedTime)
        if elapsedTime > time.Duration(100) * time.Millisecond {
            break
        }
        var random = rand.Intn(max - min) + min
        for i := 0; i < random; i++ {
            n++
            numbers <- i
        }
        time.Sleep(time.Duration(10) * time.Millisecond)
    }

    fmt.Println("DONE", n)
}

Answer 1

Use a WaitGroup. Since numbers represent the incoming work, when you send something to numbers , you can add one to the waitgroup:

wg.Add(1)
numbers <- i

And as you read from messages, mark that work as done:

func Read(messages chan string, wg *sync.WaitGroup) {
    for m := range messages {
        wg.Done()
        fmt.Println(m)
    }
}

And, wait for the waitgroup to complete in main:

wg.Wait()
fmt.Println("DONE", n)

Declare your waitgroup where you can pass to goroutines:

wg:=sync.WaitGroup{}
go Read(messages,&wg)