HTTPX 是 FastAPI 端點中 ThreadPoolExecutor 的更安全替代方案嗎？

Concerns of Concurrent ThreadPoolExecutor Usage in FastAPI Endpoints

Problem:

Concurrent.futures.ThreadPoolExecutor is used for parallel processing, but there are concerns about its potential impact in a FastAPI endpoint. Specifically, if multiple API calls trigger the creation of too many threads, it could result in resource exhaustion and crashes.

Solution:

Rather than relying on ThreadPoolExecutor, the HTTPX library presents a safer alternative with its async API. Using HTTPX, you can create a Client and reuse it for multiple requests. To perform asynchronous operations, an AsyncClient is recommended.

HTTPX Configuration:

HTTPX allows for customization of connection pool sizes and timeout settings. For example:

limits = httpx.Limits(max_keepalive_connections=5, max_connections=10)
async with httpx.AsyncClient(limits=limits) as client:
    ...

Adjust the limits and timeout values to suit your specific requirements.

Asynchronous Request Execution:

To make multiple asynchronous requests, you can utilize asyncio.gather(). It will await the completion of each request and return a list of results in the same order as the provided tasks.

Lifecycle Management:

For handling lifespan events in the FastAPI application, consider using the lifespan dependency. This allows you to initialize and clean up resources, such as the HTTPX client, when the application starts and shuts down.

Streaming Responses:

If you need to avoid loading entire responses into memory, consider using HTTPX's streaming capabilities and FastAPI's StreamingResponse. This allows you to iteratively process chunks of the response data, providing better scalability.

Code 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):
    # Custom settings
    client = httpx.AsyncClient(...)
    yield {'client': client}
    await client.aclose()  # Close the client 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)
    # Process the responses as needed (e.g., extract data, modify content)

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