30_closing_channels.go

package gobyexample

import "fmt"

// ClosingChannelsDemo - demonstrates closing channels
func ClosingChannelsDemo() {
	// Closing a channel indicates that no more values will be sent on it.
	// This can be useful to communicate completion to the channel's receivers.

	// In this example we'll use a `jobs` channel to communicate work to be done
	// from the main goroutine to a worker goroutine. When we have no more jobs
	// for the worker we'll `close` the `jobs` channel.

	jobs := make(chan int, 5)
	done := make(chan bool)

	// Here's the worker goroutine. It repeatedly receives from `jobs` with
	// `j more := <-jobs`. In this special 2-value form of receive, the `more`
	// value will be false if `jobs` has been closed and all values in the channel
	// have already been received. We use this to notify on `done` when we've worked
	// all our jobs.
	go func() {
		for {
			j, more := <-jobs
			if more {
				fmt.Println("received job", j)
			} else {
				fmt.Println("received all jobs")
				done <- true
				return
			}
		}
	}()

	// This sends 3 jobs to the worker over the `jobs` channel,
	// then closes it.
	for j := 1; j <= 3; j++ {
		jobs <- j
		fmt.Println("sent job", j)
	}
	close(jobs)
	fmt.Println("sent all jobs")

	// We await the worker using the synchronization approach
	// we saw earlier.
	<-done
}