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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?

Answers

According to Uvicorn documentation there is no programmatically way to stop the server. instead, you can stop the server only by pressing ctrl + c (officially).

But I have a trick to solve this problem programmatically using multiprocessing standard lib with these three simple functions :

• A run function to run the server.
• A start function to start a new process (start the server).
• A stop function to join the process (stop the server).

from multiprocessing import Process
import uvicorn

# global process variable
proc = None


def run(): 
    """
    This function to run configured uvicorn server.
    """
    uvicorn.run(app=app, host=host, port=port)


def start():
    """
    This function to start a new process (start the server).
    """
    global proc
    # create process instance and set the target to run function.
    # use daemon mode to stop the process whenever the program stopped.
    proc = Process(target=run, args=(), daemon=True)
    proc.start()


def stop(): 
    """
    This function to join (stop) the process (stop the server).
    """
    global proc
    # check if the process is not None
    if proc: 
        # join (stop) the process with a timeout setten to 0.25 seconds.
        # using timeout (the optional arg) is too important in order to
        # enforce the server to stop.
        proc.join(0.25)

With the same idea you can :

• use threading standard lib instead of using multiprocessing standard lib.

• refactor these functions into a class.

Example of usage :

from time import sleep

if __name__ == "__main__":
    # to start the server call start function.
    start()
    # run some codes ....
    # to stop the server call stop function.
    stop()

You can read more about :

• Uvicorn server.
• multiprocessing standard lib.
• threading standard lib.
• Concurrency to know more about multi processing and threading in python.