FastAPI lifetime tests

app.py

from fastapi import FastAPI
from lock import FileLock

app = FastAPI()
lock = FileLock("fastapi")

@app.get("/")
async def root():
    return {"message": "Hello World"}

# Already, the lock doesn't get released anymore,
# even when shutting down uvicorn properly

app2.py

from fastapi import FastAPI
from lock import FileLock

app = FastAPI()
lock: FileLock

@app.on_event("startup")
def take_lock():
	global lock
	lock = FileLock("fastapi")

@app.on_event("shutdown")
def release_lock():
	global lock
	del lock

@app.get("/")
async def root():
    return {"message": "Hello World"}

lock.py

import sys
from pathlib import Path

class FileLock:
	def __new__(cls, lockname: str):
		lockpath = Path(sys.path[0]) / f'{lockname}.lock'

		try:
			lockpath.touch(exist_ok=False)
			print("Lock taken!")

			self = super(FileLock,cls).__new__(cls)
			self.lockpath = lockpath
			return self
		except FileExistsError as ex:
			print("Someone else has the lock :(")
			raise ex

	def __del__(self):
		try:
			self.lockpath.unlink()
			print("Lock released!")
		except FileNotFoundError as ex:
			print("What happenned to the lock??")
			raise ex

test.py

from lock import FileLock
from time import sleep

lock = FileLock("test_lock")
print("You'd better not try to start another instance of this, now! No siree!")
sleep(3600)
print("Ok, all done!")
# The lock should release itself once garbage collected
# before the interpreter exits.

See tiangolo/fastapi#617.