# A very simple example of a coroutine/generator scheduler

# Two simple generator functions
def countdown(n):
    while n > 0:
        print("T-minus", n)
        yield
        n -= 1
    print("Blastoff!")

def countup(n):
    x = 0
    while x < n:
        print("Counting up", x)
        yield
        x += 1

from collections import deque

class TaskScheduler:
    def __init__(self):
        self._task_queue = deque()

    def new_task(self, task):
        '''
        Admit a newly started task to the scheduler
        '''
        self._task_queue.append(task)

    def run(self):
        '''
        Run until there are no more tasks
        '''
        while self._task_queue:
            task = self._task_queue.popleft()
            try:
                # Run until the next yield statement
                next(task)
                self._task_queue.append(task)
            except StopIteration:
                # Generator is no longer executing
                pass

# Example use
sched = TaskScheduler()
sched.new_task(countdown(10))
sched.new_task(countdown(5))
sched.new_task(countup(15))
sched.run()