Simple synchronous route seems to block app

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Example Code

from fastapi import FastAPI, Request, Depends, HTTPException, status
import uvicorn
import time

app = FastAPI()

@app.get('/')
def main():
    time.sleep(5)
    return []

uvicorn.run(app, host="127.0.0.1", port=5001)

Description

I expect this code to be non-blocking, since it is declared using a regular def instead of async def, meaning each time I open the main route, it should load in a separate thread. However, when I run this application, and open up the / route on multiple tabs in my browser, it is clear that the app is running synchronously. It takes 5 seconds for each tab to load the route, starting from the time the previous tab is loaded. So if I open 4 tabs, it takes about 20 seconds for the last tab to load.

Am I misunderstanding something? Is there a way to get code like this to run so that each time the page is loaded, it doesn’t block other pages from being loaded?

Operating System

Windows

Operating System Details

No response

FastAPI Version

0.70.1

Python Version

3.9.5

Additional Context

No response

[abidlabs]

Ohhhhhh, interesting. Thanks for letting me know!

[ycd]

This is not related to the FastAPI, conversely it is a browser feature.

See the similar issues: https://github.com/tiangolo/fastapi/issues/2786 https://github.com/tiangolo/fastapi/issues/3697

In chromium there is a cache that prevents sending the same requests to same URL to avoid downloading the same data over and over again by adding a 20 second timeout to cache.

If you are interested in how it works check this issue in chromium.

See: https://codereview.chromium.org/345643003