How to schedule and cancel tasks with asyncio
<p>I am writing a client-server application. While connected, client sends to the server a "heartbeat" signal, for example, every second.
On the server-side I need a mechanism where I can add tasks (or coroutines or something else) to be executed asynchronously. Moreover, I want to cancel tasks from a client, when it stops sending that "heartbeat" signal. </p>

<p>In other words, when the server starts a task it has kind of timeout or <em>ttl</em>, in example 3 seconds. When the server receives the "heartbeat" signal it resets timer for another 3 seconds until task is done or client disconnected (stops send the signal).</p>

<p>Here is an <a href="https://pymotw.com/3/asyncio/index.html" rel="noreferrer">example</a> of canceling a task from <em>asyncio</em> tutorial on pymotw.com. But here the task is canceled before the event_loop started, which is not suitable for me.</p>

<pre><code>import asyncio

async def task_func():
    print('in task_func')
    return 'the result'


event_loop = asyncio.get_event_loop()
try:
    print('creating task')
    task = event_loop.create_task(task_func())

    print('canceling task')
    task.cancel()

    print('entering event loop')
    event_loop.run_until_complete(task)
    print('task: {!r}'.format(task))
except asyncio.CancelledError:
    print('caught error from cancelled task')
else:
    print('task result: {!r}'.format(task.result()))
finally:
    event_loop.close()
</code></pre>