Asynchronous Calls with HTTPX in FastAPI Endpoints
Concerns About Using ThreadPoolExecutor in FastAPI
You expressed concerns about the impact of using concurrent.futures.ThreadPoolExecutor in a FastAPI endpoint, particularly regarding thread creation, host starvation, and application crashes. These concerns are valid since excessive thread creation can strain resources and potentially lead to performance issues.
Recommendation: HTTPX Async API
To avoid these potential pitfalls, it's recommended to utilize the async capabilities of the HTTPX library instead of concurrent.futures.ThreadPoolExecutor. HTTPX provides an efficient asynchronous API that allows you to make HTTP requests without the need for explicit thread management. This approach offers several advantages:
Working Example
The following code snippet demonstrates how to implement asynchronous HTTP requests with HTTPX in a FastAPI endpoint:
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) # 15s timeout on read. 5s timeout elsewhere. # 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
Alternative: Streaming Responses to Avoid RAM Usage
If reading the entire response bodies into RAM is a concern, consider utilizing HTTPX's Streaming responses along with FastAPI's StreamingResponse:
... # (same as previous code snippet) async def iter_content(responses): for r in responses: async for chunk in r.aiter_text(): yield chunk[:50] # for demo purposes, return only the first 50 chars of each response and then break the loop yield '\n\n' break await r.aclose() @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 StreamingResponse(iter_content(responses), media_type='text/event-stream')
The above is the detailed content of How can I avoid resource strain and potential crashes when making concurrent HTTP calls in a FastAPI endpoint?. For more information, please follow other related articles on the PHP Chinese website!