blocking_api.py

"""
Non blocking example:
1. Browse to `localhost:8000/sleep1`
2. Browse to `localhost:8000/`

You'll observe that the first call will take 5 seconds and the second call will be executed immediately.

Blocking example:
1. Browse to `localhost:8000/sleep2`
2. Browse to `localhost:8000/`

You'll observe that the second call will be blocked by the first call. After the first call is executed it will execute
the second.
"""
import uvicorn
import time
from fastapi import FastAPI
from starlette.concurrency import run_in_threadpool as pool

app = FastAPI()


@app.get("/")
def read_root():
    # This will go to the 'Event loop'
    # The event loop decides to execute it in a threadpool
    return {"Hello": "World"}


@app.get("/sleep1")
def sleep1():
    # This will go to the 'Event loop'
    # The event loop decides to execute it in a threadpool
    time.sleep(5)
    return {}


@app.get("/sleep2")
async def sleep2():
    # This will be executed in the 'Event loop'
    # This will block the entire 'Event loop' since time.sleep() is a synchronous method
    time.sleep(5)
    return {}


@app.get("/sleep3")
async def sleep3():
    print("A")
    await pool(time.sleep, 5)
    print("B")
    return {}

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)