[Bugfix] fix race condition that leads to wrong order of token returned

[joennlae]

The setup function is called multiple times (every 5 seconds) during the API server's startup. The longer the startup time (generally for larger models), the more consumers are contending for the output. This can lead to a race condition where the order of the answer token is wrong.

Here is where the setup function is called:

vllm/vllm/entrypoints/openai/api_server.py

Lines 205 to 217 in c11f172

	try:
	while True:
	try:
	await mq_engine_client.setup()
	break
	except TimeoutError:
	if (not engine_process.is_alive()
	or not engine_alive.value):
	raise RuntimeError(
	"Engine process failed to start. See stack "
	"trace for the root cause.") from None
	yield mq_engine_client # type: ignore[misc]

Introduced here: #9973

References:
#10376
#10589
#10782

[github-actions]

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