Event handler not called asynchrously

[ghost]

I'm using self.screen.post_message(LogMessage(message)) to log to a TextLog widget.
The logging generally works, but even though it is async, the on_log_message handler is only called with delay.

    async def action_reschedule_all(self):
        task = asyncio.create_task(self.action_reschedule_all_task())

    async def action_reschedule_all_task(self):
        async for result in <async generator object>:
            ...
            self.screen.post_message(LogMessage(message))

    async def on_log_message(self, message: LogMessage):
        self.log(datetime.now().isoformat())
        self.query_one("#log", TextLog).write(message.message)

logged timestamps are as follows:

2023-05-15T08:57:03.723885 - action_reschedule_all_task
2023-05-15T08:57:05.669832 - action_reschedule_all_task
2023-05-15T08:57:05.669832 - on_log_message
2023-05-15T08:57:05.671770 - on_log_message

as you can see action_reschedule_all_task was running async, but on_log_message was not called async.
Am I doing something wrong or is this a bug?

[willmcgugan]

You may need to clarify what you are reading from those timestamps. What would you expect to see? But more importantly: why would you expect to see it.

[ghost]

I would expect the first on_log_message timestamp to be directly after the first action_reschedule_all_task timestamp.
Because the LogMessage was posted using post_message right there, as the timestamp of the first action_reschedule_allt_task proofs.

[willmcgugan]

That is not necessarily going to happen. post_message adds it to a queue, for the widget's task to pick up. When that happens depends on a number of things, such as how busy your widget / app is, and how asyncio choses to schedule things. All post_message guarantees is that the message will be handled at some point in the near future.

[ghost]

I see.
Is there a recommended alternative approach for scenarios where fluid updates are required on another Screen?

[willmcgugan]

You are calling time.sleep which is not asynchronous. It will prevent asyncio from doing anything at all during that time.

If you have a blocking long running task, you should run it in a thread. The @work decorator will help you there.

[ghost]

I'm new to asyncio, but as far as I understand the code I actually use is non-blocking (a request using httpx).
If I replace time.sleep with await asyncio.sleep in the minimal example above I get the same results.
Does await cause the request to become blocking?

[ghost]

Ah made a mistake with httpx, should have used AsyncClient. Now it is working with async.

[ghost]

Thanks a lot for your support, makes it really fun working with textual!

[willmcgugan]

No problem. Glad you are enjoying it!