Python - How to use FastAPI and uvicorn.run without blocking the thread?

Question

I'm looking for a possibility to use uvicorn.run() with a FastAPI app but without uvicorn.run() is blocking the thread. I already tried to use processes, subprocessesand threads but nothing worked. My problem is that I want to start the Server from another process that should go on with other tasks after starting the server. Additinally I have problems closing the server like this from another process.

Has anyone an idea how to use uvicorn.run() non blocking and how to stop it from another process?

Greetings LeukoClassic

Answer 1

Approach given by @HadiAlqattan will not work because uvicorn.run expects to be run in the main thread. Errors such as signal only works in main thread will be raised.

Correct approach is:

import contextlib
import time
import threading
import uvicorn

class Server(uvicorn.Server):
    def install_signal_handlers(self):
        pass

    @contextlib.contextmanager
    def run_in_thread(self):
        thread = threading.Thread(target=self.run)
        thread.start()
        try:
            while not self.started:
                time.sleep(1e-3)
            yield
        finally:
            self.should_exit = True
            thread.join()

config = Config("example:app", host="127.0.0.1", port=5000, log_level="info")
server = Server(config=config)

with server.run_in_thread():
    # Server is started.
    ...
    # Server will be stopped once code put here is completed
    ...

# Server stopped.

Very handy to run a live test server locally using a pytest fixture:

# conftest.py
import pytest

@pytest.fixture(scope="session")
def server():
    server = ...
    with server.run_in_thread():
        yield

Credits: uvicorn#742 by florimondmanca