@Marvin I am getting this error

RuntimeError: This event loop is already running

ever since I've upgraded from Prefect 2 to Prefect 3. Do you have any advice on how to fix this?

The issue you're experiencing with Prefect 3, "RuntimeError: This event loop is already running," is often encountered when dealing with asynchronous operations in Python, especially when using libraries like Prefect that handle concurrency and event loops. Below are some insights and suggestions to help you resolve this problem: 1. Use of Asynchronous Flows: Prefect 3.x documentation indicates that it runs all code on the main thread by default, which can lead to event loop issues if you're trying to run asynchronous code or multiple flows in parallel. 2. Parallel Flow Execution: A related GitHub issue (#9296) suggests that Prefect currently does not support running multiple concurrent runs of the same flow instance using multi-threading, due to limitations related to the Global Interpreter Lock (GIL) in Python. This could be contributing to the "already running" event loop error. 3. Potential Workarounds: - Separate Event Loops: If possible, ensure each flow or concurrent operation has its dedicated event loop. This might mean restructuring your flows to isolate asynchronous calls. - Thread Pool: Use a thread pool or a different execution context that handles threads separately from the event loop being used by Prefect. - Asyncio Calls: Be cautious with how you call asyncio functions. Using

asyncio.run()

in Prefect might not be appropriate as Prefect might already be using an event loop under the hood. If these general suggestions do not resolve your issue, you might want to look at the specific Prefect configurations or flow structures you are using. You can refer to the Prefect 3.x Troubleshooting Guide for more detailed troubleshooting related to concurrency and event loops. If you're interested in more detailed solutions, the Prefect community and GitHub issues tracker can be valuable resources for workarounds and updates on this topic.