Playground and sample for mastering Kotlin

Coroutines are concurrent. And can run in parallel.

Think of Coroutines as lightweight threads that are used to perform tasks asynchronously, a.k.a. non-blocking programming.

Coroutine are so lightweight that you can easily create a thousand of them without any performance concern.

To debug coroutines : -Dkotlinx.coroutines.debug

They are essentially the same. launch is a "fire and forget" kind of task, async will return some result.

You should always keep a reference to an async coroutine

Blocking means that a function call will pause the execution of the programme until that function is done.

When you are in a non blocking context, the next line of code will be executed even if a function has not returned it value yet.

Kotlin helper function to make blocking call of coroutines (wait that coroutine finish before executing next line of code)

• runBlocking
• measureTimeMillis
• withTimeoutOrNull
• ...

• blocking
• concurrent
• A suspending function is a regular function that suspend the execution of the calling coroutine.

A Job is a reference to a coroutine that can have children and a parent.

• A Job gives you a control over a coroutine.
• Job have a lifecycle

You can use SupervisorJob to keep control over children coroutines executions.

:::spoiler Behaviors of Jobs

• Cancellation of parent with cancel or its exceptional completion (failure) immediately cancels all its children.
• Parent cannot complete until all its children are complete. Parent waits for all its children to complete in completing or cancelling state.
• Uncaught exception in a child, by default, cancels parent. In particular, this applies to children created with launch coroutine builder. Note, that async and other future-like coroutine builders do not have uncaught exceptions by definition, since all their exceptions are caught and are encapsulated in their result. :::

A dispatcher is a pool of threads that have a specific role / task and is optimized for it by the language.

• Dispatchers.IO
• Dispatchers.Unconfined
• Dispatchers.Main
• Dispatchers.Default

A coroutine Scope is what tie everything together with control.

It's recommended by Kotlin to create your own coroutine scope and not use the GlobalScope which handle many jobs and can conflict with your work (or you can conflict with its job)

//My supervisor job to have it as parent of
//every jobs that are created from this coroutine scope
val mySupervisorJob = SupervisorJob()

//Exception handler on which all coroutines exceptions
// will be traced back
val handler = CoroutineExceptionHandler { context, exception ->
    println("$context with exception=${exception.message}")
}

//Finally my super CoroutineScope
val coroutineScopeCustom = CoroutineScope(Dispatchers.IO 
                                + mySupervisorJob 
                                + handler)

• blocking
• synchronous
• Synchronous and sequential treatment of a list
• https://kotlinlang.org/docs/reference/sequences.html

• non-blocking
• concurrent
• hot
• Hot stream of data, channel are used to treat data as continous streams. Channel live inside coroutines and can exchange data between coroutines.

• non-blocking
• concurrent
• cold
• Cold stream of data. Flow are like Sequence but asynchronous. Each step of a Flow transformation is async and non-blocking.

Backpressure happen when an Observable produce quicker than it(s) observers can ingest.

• http://reactivex.io/documentation/operators/backpressure.html