Is using a `concurrent.futures.ThreadPoolExecutor` in a FastAPI endpoint risky?

Is It Risky to Use a Concurrent.futures.ThreadPoolExecutor in a FastAPI Endpoint?

Problem Statement:

In the provided test code, a ThreadPoolExecutor is used to retrieve data from multiple websites concurrently. The concern is that using this approach in a FastAPI endpoint could lead to excessive thread creation and potential issues like resource starvation and application crashes.

Concerns and Potential Gotchas:

• Thread Exhaustion: Creating too many threads can deplete the system's thread pool, leading to thread starvation and potentially crashing the application or host.
• Resource Contention: Threads compete for system resources, such as memory and CPU, which can slow down the application and impact performance.
• Synchronizability: Managing synchronization between threads in a multi-threaded environment can be complex and introduces potential for race conditions.

Recommended Solution: Using HTTPX Library

Instead of using a ThreadPoolExecutor, it is advisable to employ the HTTPX library, which offers an asynchronous API. HTTPX provides a number of advantages:

• Asynchronous Operation: HTTPX works asynchronously, allowing for efficient handling of concurrent requests without blocking the thread pool.
• Connection Pool Management: It automatically manages connection pools, ensuring connections are reused and limiting the number of active connections.
• Fine-Grained Control: HTTPX allows customization of connection limits and timeouts, providing precise control over resource usage.
• Simplified Integration with FastAPI: FastAPI can be integrated with HTTPX seamlessly, utilizing the async support provided by the framework.

Working Example:

from fastapi import FastAPI, Request
from contextlib import asynccontextmanager
import httpx
import asyncio

URLS = ['https://www.foxnews.com/',
        'https://edition.cnn.com/',
        'https://www.nbcnews.com/',
        'https://www.bbc.co.uk/',
        'https://www.reuters.com/']

@asynccontextmanager
async def lifespan(app: FastAPI):
    # Customise settings
    limits = httpx.Limits(max_keepalive_connections=5, max_connections=10)
    timeout = httpx.Timeout(5.0, read=15.0)  # 5s timeout on all operations

    # Initialise the Client on startup and add it to the state
    async with httpx.AsyncClient(limits=limits, timeout=timeout) as client:
        yield {'client': client}
        # The Client closes on shutdown

app = FastAPI(lifespan=lifespan)

async def send(url, client):
    return await client.get(url)

@app.get('/')
async def main(request: Request):
    client = request.state.client
    tasks = [send(url, client) for url in URLS]
    responses = await asyncio.gather(*tasks)
    return [r.text[:50] for r in responses]  # For demo purposes, only return the first 50 chars of each response

This code snippet demonstrates the use of HTTPX with FastAPI to handle concurrent requests asynchronously, effectively mitigating the concerns associated with thread exhaustion and resource contention.

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