vLLM accelerated deployment streamed batching lab

# code example from https://github.com/ray-project/ray/blob/cc983fc3e64c1ba215e981a43dd0119c03c74ff1/doc/source/serve/doc_code/vllm_example.py

import json
from typing import AsyncGenerator

from fastapi import BackgroundTasks
from starlette.requests import Request
from starlette.responses import StreamingResponse, Response
from vllm.engine.arg_utils import AsyncEngineArgs
from vllm.engine.async_llm_engine import AsyncLLMEngine
from vllm.sampling_params import SamplingParams
from vllm.utils import random_uuid

from ray import serve


@serve.deployment(ray_actor_options={"num_gpus": 1})
class VLLMPredictDeployment:
    def __init__(self, **kwargs):
        """
        Construct a VLLM deployment.

        Refer to https://github.com/vllm-project/vllm/blob/main/vllm/engine/arg_utils.py
        for the full list of arguments.

        Args:
            model: name or path of the huggingface model to use
            download_dir: directory to download and load the weights,
                default to the default cache dir of huggingface.
            use_np_weights: save a numpy copy of model weights for
                faster loading. This can increase the disk usage by up to 2x.
            use_dummy_weights: use dummy values for model weights.
            dtype: data type for model weights and activations.
                The "auto" option will use FP16 precision
                for FP32 and FP16 models, and BF16 precision.
                for BF16 models.
            seed: random seed.
            worker_use_ray: use Ray for distributed serving, will be
                automatically set when using more than 1 GPU
            pipeline_parallel_size: number of pipeline stages.
            tensor_parallel_size: number of tensor parallel replicas.
            block_size: token block size.
            swap_space: CPU swap space size (GiB) per GPU.
            gpu_memory_utilization: the percentage of GPU memory to be used for
                the model executor
            max_num_batched_tokens: maximum number of batched tokens per iteration
            max_num_seqs: maximum number of sequences per iteration.
            disable_log_stats: disable logging statistics.
            engine_use_ray: use Ray to start the LLM engine in a separate
                process as the server process.
            disable_log_requests: disable logging requests.
        """
        args = AsyncEngineArgs(**kwargs)
        self.engine = AsyncLLMEngine.from_engine_args(args)

    async def stream_results(self, results_generator) -> AsyncGenerator[bytes, None]:
        num_returned = 0
        async for request_output in results_generator:
            text_outputs = [output.text for output in request_output.outputs]
            assert len(text_outputs) == 1
            text_output = text_outputs[0][num_returned:]
            ret = {"text": text_output}
            yield (json.dumps(ret) + "\n").encode("utf-8")
            num_returned += len(text_output)

    async def may_abort_request(self, request_id) -> None:
        await self.engine.abort(request_id)

    async def __call__(self, request: Request) -> Response:
        """Generate completion for the request.

        The request should be a JSON object with the following fields:
        - prompt: the prompt to use for the generation.
        - stream: whether to stream the results or not.
        - other fields: the sampling parameters (See `SamplingParams` for details).
        """
        request_dict = await request.json()
        prompt = request_dict.pop("prompt")
        stream = request_dict.pop("stream", False)
        sampling_params = SamplingParams(**request_dict)
        request_id = random_uuid()
        results_generator = self.engine.generate(prompt, sampling_params, request_id)
        if stream:
            background_tasks = BackgroundTasks()
            # Using background_taks to abort the the request
            # if the client disconnects.
            background_tasks.add_task(self.may_abort_request, request_id)
            return StreamingResponse(
                self.stream_results(results_generator), background=background_tasks
            )

        # Non-streaming case
        final_output = None
        async for request_output in results_generator:
            if await request.is_disconnected():
                # Abort the request if the client disconnects.
                await self.engine.abort(request_id)
                return Response(status_code=499)
            final_output = request_output

        assert final_output is not None
        prompt = final_output.prompt
        text_outputs = [prompt + output.text for output in final_output.outputs]
        ret = {"text": text_outputs}
        return Response(content=json.dumps(ret))


def send_sample_request():
    import requests

    prompt = "How do I cook fried rice?"
    sample_input = {"prompt": prompt, "stream": True}
    output = requests.post("http://localhost:8000/", json=sample_input)
    for line in output.iter_lines():
        print(line.decode("utf-8"))


if __name__ == "__main__":
    # To run this example, you need to install vllm which requires
    # OS: Linux
    # Python: 3.8 or higher
    # CUDA: 11.0 – 11.8
    # GPU: compute capability 7.0 or higher (e.g., V100, T4, RTX20xx, A100, L4, etc.)
    # see https://vllm.readthedocs.io/en/latest/getting_started/installation.html
    # for more details.
    deployment = VLLMPredictDeployment.bind(model="facebook/opt-125m")
    serve.run(deployment)
    send_sample_request()