[Bugfix][Core] Fix and refactor logging stats

[esmeetu]

Currently engine stats log will output 0 when using --engine-use-ray.
And this PR compact logging stats code by using existed function.

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[rkooo567]

This looks good. Wonder if we can add an unit test for this inside

vllm/tests/async_engine/test_api_server.py

Line 50 in b6dcb4d

def test_api_server(api_server, tokenizer_pool_size: int, worker_use_ray: bool,

? Basically just capture the stdout and verify it is printed

[esmeetu]

@rkooo567 I use capsys to capture the server output:captured = capsys.readouterr(), but it always output empty, do you know why?🤔

[rkooo567]

Hmm when you don't use capsys and run the test, does it print the server logs?

probably because api server is running in a subprocess, and their stdout/stderr is not printed. I think you can use https://docs.python.org/3/library/subprocess.html#subprocess.Popen.communicate to get stdout/stderr (in this case, you may not even need capsys)

[esmeetu]

@rkooo567 It will print log when i add args -s.
My last version is using [Popen.communicate]:

    with subprocess.Popen(commands,
                          stdout=subprocess.PIPE,
                          stderr=subprocess.STDOUT) as uvicorn_process:
        output, _ = uvicorn_process.communicate()
        output = output.decode(locale.getpreferredencoding())
        assert "prompt" in output
        yield

But this will block test. 🫠

[rkooo567]

In [13]: def f():
    ...:     from subprocess import TimeoutExpired
    ...:     proc = subprocess.Popen(["python", "a.py"])
    ...:     try:
    ...:         outs, errs = proc.communicate(timeout=3)
    ...:     except TimeoutExpired:
    ...:         proc.kill()
    ...:         outs, errs = proc.communicate()
    ...:         print(outs)
    ...:         print(errs)

I think you can make this way to terminate the subprocess?

[esmeetu]

@rkooo567 Thanks for you help. But My local test is ok while not in our CI. ☹️

[rkooo567]

Is it okay if I try something on this PR directly?

[esmeetu]

Is it okay if I try something on this PR directly?

No problem.

[rkooo567]

I took a look. I feel like we are hitting https://www.reddit.com/r/Python/comments/1vbie0/subprocesspipe_will_hang_indefinitely_if_stdout/.

I worked around it by redirecting logs to tempfile. This will hinder debuggability, so I added logs to explain how to debug.

See this PR rkooo567#25. or if you give me persmission to your repo, I can push there directly (it seems like it is not allowed)

[esmeetu]

@rkooo567 I revert test changes in this PR, can we merge this first and then submit your changes in another PR?

[rkooo567]

yeah that sgtm!

[rkooo567]

cc @cadedaniel to merge

[cadedaniel]

Thanks guys -- can we get testing in your PR @rkooo567 ?

[cadedaniel]

I am retrying the basic correctness test -- seems it failed for an infra error