How to make goroutines talk to each other using Channels

Question

I am new to Golang and am trying to use goroutines so that they can talk among them. I have some code which starts up a goroutine which has operation1, I call it to dance. When it finishes, it signals another goroutine which performs another operation2, let's say sleep.

You can pass a force dance parameter to the dance goroutine but if it is already in the dance state, it would sleep.

package main

import (
    "fmt"
    "time"
)

func main(){
    test("notdancing", true)
    time.Sleep(10*time.Second)
}
func dance()error{
    fmt.Println("Tapping my feet")
    time.Sleep(10*time.Second)
    return nil
}
func test(status string, forceDance bool) {

This does not work when

   //startSleep := make(chan bool)

Why does a channel need to be provided a buffer length to make it work? I tried without the buffer length but it says all goroutines are asleep if I don't pass 1 as the second parameter.

    startdance := make(chan bool, 1)
    startSleep := make(chan bool, 1)

    if status == "dancing" && forceDance {
        select {
        case startSleep <-true:
            fmt.Println("Would start to sleep now")
        default:
            fmt.Println("Sleep Already started. No need to force")
        }
    }

    if status != "dancing" {
        fmt.Println("Startingdance")
        startdance <- true
    }

    go func() {
        <-startdance
        err := dance()
        if err == nil {
            select {
            case startSleep <- true:
                fmt.Println("Starting Sleeping, dancing completed")
            default:
                fmt.Println("Already started Sleeping")
            }
        } else {
            fmt.Println("Not in a mood to dance today")
        }
    }()

    go func() {
        <-startSleep
        if forceDance {
            fmt.Println("Force sleep because forcing to dance while already dancing")
        }
    }()

}

I would highly appreciate any corrections to the code as well as the pitfalls of using this approach.

Answer 1

in case of Unbuffered Channel (when size is not specified) it can't hold a value as it has no size. therefore a reader has to be present at the time of writing/transmiting the data through the channel or else it will be blocking the call.

func main() {
    startDance := make(chan bool)
    startDance <- true
}

But when you specify a size in the above code (say 1) then it won't be a deadlock as it will have space to hold the data. ((https://robertbasic.com/blog/buffered-vs-unbuffered-channels-in-golang/) .)(https://www.golang-book.com/books/intro/10) you could check out the above website's to get a better understanding about channels and concurrency

package main

import (
    "fmt"
    "time"
)

func main() {
    startDance := make(chan bool)
    startSleep := make(chan bool)
    forceSleep := make(chan bool)
    go startDance1(startDance, forceSleep, startSleep)
    go performSleep(startSleep, startDance)
    startDance <- true
    fmt.Println("now dance is started ")
    forceSleep <- true
    select {}
}

func startDance1(startDance chan bool, forceSleep chan bool, startSleep chan bool) {

    fmt.Println("waiting to start dance")
    select {
    case <-startDance:
        fmt.Println("staring dance")
    }

    for {
        select {
        case <-startDance:
            fmt.Println("starting dance")
        case <-forceSleep:
            fmt.Println("aleardy dancing going to sleep")
            select {
            case startSleep <- true:

            default:
            }
        default:
            //this is just to show working this
            // i added default or else this will go into deadlock
            fmt.Println("dancing")
            time.Sleep(time.Second * 1)
        }
    }
}

func performSleep(startSleep chan bool, startDance chan bool) {
    select {
    case <-startSleep:
        fmt.Println("staring sleep")
    }
    fmt.Println("sleeping for 5 seconds ")
    time.Sleep(time.Second * 5)
    select {
    case startDance <- true:
        fmt.Println("started dance")
    default:
        fmt.Println("failed to start dance ")
    }
}

Above code is a minor improvement over yours (i tried to make it according to your requirements). I would suggest you go through some books to get to know more about go concurrency (https://www.golang-book.com/books/intro/10_