What to do if there is a blocking synchronous I/O operation in an asynchronous application (FastAPI)?

In FastAPI, which is based on asyncio, blocking synchronous I/O operations can block the entire event loop, leading to reduced performance and delays.

To solve this problem, you can:

• Offload the blocking operation to a separate thread or process using run_in_executor:

import asyncio
from fastapi import FastAPI

app = FastAPI()

def blocking_io():
    # For example, reading from a file or making a database request without async
    import time
    time.sleep(5)
    return "done"

@app.get("/blocking")
async def read_blocking():
    loop = asyncio.get_running_loop()
    result = await loop.run_in_executor(None, blocking_io)
    return {"result": result}

• Use asynchronous libraries for I/O if available (for example, httpx instead of requests, databases instead of synchronous database drivers).

• If the operation is very heavy, consider offloading it to a separate microservice or a queued task.

Thus, the blocking operation will not interfere with processing other requests.