What is a coroutine?

WhatIsACoroutine.kt

// 1
Thread {
    var counter = 0
    counter++
    counter++
    println("$counter") // will always print "2"
}

// 2
// for every Request, a Response is returned
fun handleRequest(request: Response): Reponse
// (caption) A `Response` is guaranteed to be returned on the same thread that `handleRequest(request)` was invoked on.

// 3
fun handleRequest(request: Response): Reponse {
    val userId = request.userId
    // request thread is blocked while network call is made
    val networkData = network.loadData(userId)
    return networkData.asResponse()   
}

// 4
scope.launch {
    var functionsCalled: Int = 0 // mutable shared state
    
    withContext(Dispatchers.IO) { // switch to an IO thread
        val profile = database.loadUserProfile(userId) // suspension point
        functionsCalled++
        withContext(Dispatchers.UI) { // switch to the UI thread
            ui.show(profile)
            functionsCalled++
        }    
    }
    println(functionsCalled)
}