Understanding Chan Chan's in Go

转自老外的文章：http://tleyden.github.io/blog/2013/11/23/understanding-chan-chans-in-go/

A channel describes a transport of sorts. You can send a thing down that transport. When using a chan chan, the thing you want to send down the transport is another transport to send things back.

They are useful when you want to get a response to something, and you don’t want to setup two channels (it’s generally considered bad practice to have data moving bidirectionally on a single channel)

Visual time lapse walkthrough

Keep in mind that Goroutine C is the “real consumer” even though it will be the one which writes to the request channel.

The request channel starts out empty.

Goroutine C passes a “response channel” to go routine D via the request channel

Goroutine C starts reading from the (still empty) response channel.

Goroutine D writes a string to the response channel

Goroutine C now is able to read a value from response channel, and get’s the “wassup!” message

And now we are back to where we started

Here is some code that uses chan chan’s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

package main import "fmt" import "time" func main() { // make the request chan chan that both go-routines will be given requestChan := make(chan chan string) // start the goroutines go goroutineC(requestChan) go goroutineD(requestChan) // sleep for a second to let the goroutines complete time.Sleep(time.Second) } func goroutineC(requestChan chan chan string) { // make a new response chan responseChan := make(chan string) // send the responseChan to goRoutineD requestChan <- responseChan // read the response response := <-responseChan fmt.Printf("Response: %v\n", response) } func goroutineD(requestChan chan chan string) { // read the responseChan from the requestChan responseChan := <-requestChan // send a value down the responseChan responseChan <- "wassup!" }

This code can be run on Go playground