Coroutines, key Concepts

Basically, a coroutine is a Thread... a lightweight one, you can run a bunch of coroutines without even notice. They help us to manages our async code and their syntax is simple and easy to understand.

//Basic Example
fun main () {
    GlobalScope.launch {
        delay(2000)
        println("Hello world")
    }
    Thread.sleep(3000)
}

What is Scope?
Scope create, run, and stop Coroutines, also provides lifecycle methods.

• GlobalScope.launch{}: the scope of these coroutines will be the entire application, so when the app stops the coroutine will stop.
• runBlocking: it will run on the main thread. Runs a new coroutine and blocks the current thread interruptible until its completion.
• CoroutineScope: it will create a new scope and will run until all the inner coroutines finish.

Examples:

fun main () {
  runBlocking {
     launch {
     println("runBlocking ")
     }
  }

  GlobalScope.launch {
     println("runBlocking")
  }

   coroutineScope {
      launch {
    println("runBlocking")
      }
  }
}

What is Context?

It's a set of variables and data associated with the coroutines.

• Dispatcher: Specify the thread in which our coroutine will run
• Job: Handle the coroutine lifecycle.

What is a Suspending function?

It's a function that can be run in a Coroutine. So the only difference is that we need to add the 'suspended' key-word at the beginning.

suspend fun myFunction(){
    println("Hello, I'm suspended")
}

What is a Job?

A job is the result of the '.launch()', so we can store this in a variable and use it. ( That way we can manipulate the lyfecycle of the corotutine).

   val job = GlobalScope.launch {
      // Coroutine work...
   }

What is a Dispatcher?

Manage in which thread the coroutine will run. We can specify (if we want) in which thread our coroutine will run and switch between threads with the keyword: withContext

Common dispatchers:

launch(Dispatchers.Main) { // Main -- will work with main thread (UI)
    println("Main")
}
launch(Dispatchers.IO) { // IO -- will work with IO thread, network or file work
    println("IO")
}
launch(Dispatchers.Unconfined) { // not confined -- will work with main thread
    println("Unconfined")
}
launch(Dispatchers.Default) { // will get dispatched to DefaultDispatcher 
    println("Default")
}

withContext :
Let us change the context of our coroutine.

fun main() { 
   runBlocking {
    launch(Dispatchers.Default){
        println(“Default context”)
        withContext(Dispatchers.IO){        
           println(“IO context”)
       }   
                println(“Default context”)
    }   
  }
}

What is a Deferred?

A future result of a coroutine, for example, the result for an API call. So we need to wait for this value and we are going to use async.

fun main (){
  runBlocking {
     val myDefferred = async { suspendfun() }
  }
}

suspend fun suspendfun(): Int {
    delay(50000)
    return 10
}