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sglang/python/sglang/test/kits/basic_scheduler_stress_kit.py
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Python

"""Basic scheduler / cache / streaming stress sanity kit.
Probes that catch bugs which only fire under multi-request or large-
prompt conditions: scheduler hangs, radix prefix-cache cross-
contamination, chunked-prefill multi-chunk kernel crashes, and SSE
streaming corruption.
Mix into any ``CustomTestCase`` subclass that exposes ``self.base_url``
and ``self.process``."""
import json
import threading
import requests
_REQUEST_TIMEOUT = 120
# Shared prefix forces all concurrent requests through the same radix
# match path; per-request suffix branches the tail so the model still
# has to predict different tokens (otherwise outputs would be identical
# and we'd be testing 1 request 8 times instead of 8 independent reqs).
_CONCURRENT_PREFIX = "You are a helpful assistant. Answer with a single word.\n"
_CONCURRENT_QA = [
("Q: What is the capital of France?\nA:", "paris"),
("Q: What is the capital of Germany?\nA:", "berlin"),
("Q: What is the capital of Italy?\nA:", "rome"),
("Q: What is the capital of Japan?\nA:", "tokyo"),
("Q: What is the capital of Spain?\nA:", "madrid"),
("Q: What is the capital of Egypt?\nA:", "cairo"),
("Q: What is the capital of Russia?\nA:", "moscow"),
("Q: What is the capital of Australia?\nA:", "canberra"),
]
class BasicSchedulerStressMixin:
"""Streaming + concurrent + long-prompt path probes."""
sanity_max_new_tokens_short: int = 64
def _stress_generate(self, prompt: str, max_new_tokens: int) -> str:
resp = requests.post(
self.base_url + "/generate",
json={
"text": prompt,
"sampling_params": {
"temperature": 0.0,
"max_new_tokens": max_new_tokens,
},
},
timeout=_REQUEST_TIMEOUT,
)
self.assertEqual(resp.status_code, 200)
return resp.json()["text"]
def test_streaming_response(self):
# SSE streaming exercises a different return path than non-stream
# /generate. Catches token-by-token streaming corruption and SSE
# framing bugs without changing the model.
with requests.post(
self.base_url + "/generate",
json={
"text": "Q: What is the capital of France?\nA:",
"sampling_params": {
"temperature": 0.0,
"max_new_tokens": self.sanity_max_new_tokens_short,
},
"stream": True,
},
stream=True,
timeout=_REQUEST_TIMEOUT,
) as resp:
self.assertEqual(resp.status_code, 200)
chunks_seen = 0
last_text = ""
for raw in resp.iter_lines(decode_unicode=True):
if not raw or not raw.startswith("data:"):
continue
payload = raw[len("data:") :].strip()
if payload == "[DONE]":
break
obj = json.loads(payload)
last_text = obj.get("text", last_text)
chunks_seen += 1
self.assertGreater(chunks_seen, 0)
self.assertIn("paris", last_text.lower())
def test_concurrent_requests(self):
# 8 parallel reqs share a system prefix but each has a distinct
# question suffix. Shared prefix exercises radix prefix caching
# across concurrent reqs; per-request suffix forces independent
# decode tails (different canonical answers). Catches concurrent
# scheduler hangs and prefix-cache cross-contamination.
results = [None] * len(_CONCURRENT_QA)
def worker(idx, suffix, expected):
try:
out = self._stress_generate(
_CONCURRENT_PREFIX + suffix,
self.sanity_max_new_tokens_short,
)
results[idx] = expected in out.lower()
except Exception:
results[idx] = False
threads = [
threading.Thread(target=worker, args=(i, suffix, expected))
for i, (suffix, expected) in enumerate(_CONCURRENT_QA)
]
for t in threads:
t.start()
for t in threads:
t.join(timeout=_REQUEST_TIMEOUT)
passed = sum(1 for r in results if r)
# Tolerate one stochastic miss; gibberish would fail all 8.
self.assertGreaterEqual(
passed,
len(_CONCURRENT_QA) - 1,
f"concurrent answers correct: {passed}/{len(_CONCURRENT_QA)}; results={results}",
)
def test_long_prompt(self):
# ~8k-token filler drives the chunked-prefill path through
# multiple chunks. Catches DeepEP / large-prompt kernel crashes
# that only fire on multi-chunk prefill.
filler = "the quick brown fox jumps over the lazy dog. " * 800
out = self._stress_generate(
f"Read the following text and then answer.\n{filler}\n\n"
"Q: What is the capital of France?\nA:",
self.sanity_max_new_tokens_short,
)
# Long-prompt substring match is best-effort (model may get
# distracted); primary assertion is the 200 + non-empty inside
# _stress_generate.
self.assertGreater(len(out), 0)