Fibers

---

Fiber

Fibers are user-space threads without a scheduler; a Fiber can yield and resume its execution from the place it has exited. A Fibers (or coroutine as called in other languages) are special functions that can be interrupted at any time by the user.

When a conventional function is invoked, execution begins at the start, and once a function exits, it is finished. By contrast, Fibers can exit by calling other Fibers, which may later return to the point where they were invoked in the original coroutine:

    func main() {
        var fiber = Fiber.create({
            System.print("fiber 1");
            Fiber.yield()
            System.print("fiber 2");
        });

        System.print("main 1");
        fiber.call()
        System.print("main 2");
        fiber.call()
        System.print("main 3");
    }
    // Output:
    // main 1
    // fiber 1
    // main 2
    // fiber 2
    // main 3

A Fiber is created with create:

    Fiber.create( {
        System.print("\(self) is the current fiber")
    })

and executed till the next yield with fiber.call()

var closure = {
    System.print("1")
    Fiber.yield()

    System.print("2")
    Fiber.yield()

    System.print("3")
    Fiber.yield()

    System.print("Done")
}

var fiber = Fiber.create(closure)

fiber.call()
// prints 1

fiber.call()
// prints 2

fiber.call()
// prints 3

fiber.call()
// prints Done

System.print(fiber.isDone())
// prints true

There are 2 types of yield:

1. Fiber.yield() it returns the controll to the function calling call()
2. Fiber.yieldWaitTime(seconds) it returns the controll to the function calling call() and also store the current time internally.

The later enable a call check of the total time in seconds passed since last call(). If the time amount is not enough the call is void and the fiber is not entered.

Example:

To implement a function that do some stuff every second, like a timer, a way is to use Fiber.yieldWaitTime(seconds)

var fiber = Fiber.create({
  var keepGoing = true
  while (keepGoing) {
    keepGoing = doSomeStuff()
    Console.write("Waiting")
    Fiber.yieldWaitTime(1.0)
    Console.write("Elapsed time: \(self.elapsedTime())")
  }
})

...
// Note: this strict loop is just for reference, not a real case.
while (!fiber.isDone()) {
  fiber.call()
}