TimeoutError
asyncio.exceptions.TimeoutError
Stack trace
Traceback (most recent call last):
File "app.py", line 42, in <module>
results = await llm.generate_async(requests)
File "/usr/local/lib/python3.9/site-packages/vllm/engine.py", line 210, in generate_async
await asyncio.wait_for(self._generate(requests), timeout=30)
File "/usr/lib/python3.9/asyncio/tasks.py", line 481, in wait_for
raise exceptions.TimeoutError()
asyncio.exceptions.TimeoutError Why it happens
The vLLM async generation engine uses asyncio.wait_for to limit generation time. If the model takes longer than the specified timeout (default 30 seconds) due to large inputs, heavy load, or insufficient resources, this TimeoutError is raised.
Detection
Monitor your async generation calls with try/except catching asyncio.TimeoutError and log the request size and system load to detect slowdowns before failure.
Causes & fixes
The generation timeout is too short for the input size or model complexity.
Increase the timeout parameter in the generate_async call to allow more time for generation.
System resource constraints (CPU, GPU, memory) cause slow model inference.
Optimize resource allocation, reduce batch size, or run on more powerful hardware to speed up generation.
Heavy concurrent load on the vLLM engine causing queuing delays.
Limit concurrent requests or implement request queuing with backpressure to avoid overload.
Code: broken vs fixed
import asyncio
from vllm import LLM
llm = LLM(model="llama-3.2")
async def main():
requests = ["Hello, world!"]
# This line triggers TimeoutError if generation takes too long
results = await llm.generate_async(requests, timeout=30)
print(results)
asyncio.run(main())import asyncio
from vllm import LLM, SamplingParams
llm = LLM(model="llama-3.2")
async def main():
requests = ["Hello, world!"]
# Increased timeout to 60 seconds to prevent timeout errors
outputs = llm.generate(requests, SamplingParams(timeout=60))
print(outputs[0].outputs[0].text)
import asyncio
asyncio.run(main())Workaround
Wrap the generate call in try/except catching asyncio.TimeoutError, then retry the request with an increased timeout or fallback to synchronous generation.
Prevention
Architect your system to monitor generation latency and dynamically adjust timeouts or scale resources to prevent timeouts under load.