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A guide on how to run functions concurrently using `asyncio` in FastAPI. Learn the right techniques to avoid common pitfalls and ensure your functions complete efficiently.
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How to Properly Run Functions Concurrently in asyncio with FastAPI

FastAPI is a modern, fast web framework for building APIs with Python 3.6+ based on standard Python type hints. Utilizing asynchronous programming with FastAPI can significantly enhance performance by allowing your application to handle multiple tasks concurrently. In this post, we will address a common question faced by many developers: How do you properly run functions concurrently using asyncio in FastAPI?

The Problem

While trying to execute multiple long-running tasks simultaneously in FastAPI, many developers encounter the following error:

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This commonly happens when creating a new event loop incorrectly in an environment where an event loop is already running. If you're working with FastAPI, it's essential to understand that it manages an event loop for you.

The Solution: Simplified Code for Concurrent Execution

Step 1: Define Your Asynchronous Functions

To run functions concurrently in asyncio, you first need to define your asynchronous functions.

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Step 2: Gather and Combine Results

Instead of creating a new event loop, you should use asyncio.gather to run your asynchronous functions. This built-in method allows you to wait for multiple awaitables:

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Step 3: Create Your FastAPI Endpoint

After retrieving the combined results from the get_data() function, you can create a FastAPI endpoint to return the results:

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Final Code Structure

Here’s what the entire setup looks like:

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Conclusion

By following the outlined steps, you will be able to execute functions concurrently using asyncio in FastAPI without running into the complications of managing event loops manually. The key takeaway is that FastAPI handles the event loop, allowing you to focus on writing clear and efficient asynchronous code.

This structured approach not only prevents runtime errors but also enhances the performance of your API significantly.

Now you can confidently implement concurrent functions in your FastAPI applications!