Asynchronous programming in Marcel¶

This feature is currently under development and is therefore not available yet.

Marcel provides an async/await paradigm allowing to execute tasks in the backgrounds. In Marcel, asynchronous (AKA async) code will be executed on background threads (virtual threads if you JRE supports it).

Usage¶

Async functions¶

Async functions provide a way to write functions that are executed in the background when called

async fun int compute() {
  Thread.sleep(2000l)
  return 1
}

The actual return type of async functions are Futures (in above example a Future<Integer>).

Async block¶

An async code block is a block in which you can perform async operations

async fun int doCompute() -> 1

async {
  int result = await(doCompute())
  result
}

async blocks will always wait (at the end) for all asynchronous tasks to complete. Although this is done automatically, you can also do it manually with the await function.

Async context¶

It's important to know that async functions can only be executed in an async context., that is in an async function or in an async block (we'll get on that later).

Await¶

The await keyword allows to wait for the result of an asynchronous function.

async fun int computeInBackground() {
  int result = await doCompute()
  println(result)
}

There are many ways to await an asynchronous process.

await¶

Await is (a set of) static methods that you can use in async contexts.

await()¶

Awaits for all asynchronous tasks to complete.

await(Future)¶

Awaits for a particular asynchronous task to complete.

await(Collection), await(Object[])¶

Awaits for a collection/array of asynchronous tasks to complete.

await(AwaitProgressListener)¶

Awaits using the provider lambda to listen to progress update. E.g.

async {
  doCompute()
  await { int completedTasks, int total -> 
    print("\rComputed $completedTasks out of $total configurations")
  }
}

E.g. the below code example wouldn't compile

async fun int doCompute() -> 1

fun void computeInBackground() {
  int result = await doCompute() // Compiler error: cannot call async function in a non async context
  println(result)
}

Under the Hood of Async Programming¶

The library implementing asynchronous programming in Marcel is Threadmill, a subproject of Marcel.

How async processes are executed¶

Calling an asynchronous function will actually supply a new Callable to an executor and return the resulting Future.

Executing an async block will actually supply a new Runnable to the executor in order to execute the block in the background.