import asyncio

async def special_function
    # does some work,
    # Passes control back to controller to run main_functions
    # if they are no longer waiting.
    asyncio.sleep(0.001)

async def handler():
    tasks = [task() for task in main_tasks]

    # Adding the task that I want to run when all main_tasks are awaiting:
    tasks.append(special_function())

    await asyncio.wait(tasks)

asyncio.get_event_loop().run_until_complete(handler())