engine.py

# SPDX-License-Identifier: Apache-2.0

import pickle
import signal
from contextlib import contextmanager
from typing import Iterator, List, Optional, Union

import cloudpickle
import zmq

from vllm import AsyncEngineArgs, SamplingParams
from vllm.engine.llm_engine import LLMEngine
# yapf conflicts with isort for this block
# yapf: disable
from vllm.engine.multiprocessing import (ENGINE_DEAD_ERROR, IPC_DATA_EXT,
                                         IPC_HEALTH_EXT, IPC_INPUT_EXT,
                                         IPC_OUTPUT_EXT, REQUEST_OUTPUTS_T,
                                         VLLM_RPC_SUCCESS_STR, RPCAbortRequest,
                                         RPCAdapterLoadedResponse, RPCError,
                                         RPCLoadAdapterRequest,
                                         RPCProcessRequest,
                                         RPCResetPrefixCacheRequest,
                                         RPCStartupRequest, RPCStartupResponse,
                                         RPCUProfileRequest)
# yapf: enable
from vllm.logger import init_logger
from vllm.outputs import RequestOutput
from vllm.usage.usage_lib import UsageContext

logger = init_logger(__name__)

POLLING_TIMEOUT_MS = 10000
HEALTHY_RESPONSE = (pickle.dumps(VLLM_RPC_SUCCESS_STR), )


class MQLLMEngine:
    """A multiprocessing wrapper for :class:`LLMEngine`.

    This class is used to wrap the :class:`LLMEngine` class to enable use
    in concurrnet manner. It runs a background loop and uses zeromq to 
    receive new requests and stream outputs incrementally via ipc.
    
    The :class:`LLMEngine` generate or encode process is kicked off when a new
    RPCProcessRequest is received by the input_socket.
    
    The self.engine_loop checks the input_socket for new requests,
    adds them to the LLMEngine if there are any, calls the internal
    :class:`LLMEngine.step()`, and sends the RequestOutputs back over
    the output_socket.

    If use_async_sockets is set, the logic associated with reading new
    requests from the socket and sending data to the socket is passed
    as a callback to the llm_engine, which calls the logic asynchronously
    such that the IPC can be overlapped with the GPU.

    Args:
        ipc_path: Base path for zeromq interprocess messaging
        use_async_sockets: Whether to make send/recv async with GPU
        log_requests: Whether to log the requests.
        *args: Arguments for :class:`LLMEngine`.
        **kwargs: Arguments for :class:`LLMEngine`.
    """

    def __init__(self,
                 ipc_path: str,
                 use_async_sockets: bool,
                 *args,
                 log_requests: bool = True,
                 **kwargs) -> None:
        # For MQLLMEngine, we can use cached outputs, since each new request
        # output is immediately pickled and send over the socket, which frees
        # the python object to be reused again.
        kwargs['use_cached_outputs'] = True

        self.engine = LLMEngine(*args, **kwargs)
        self.log_requests = log_requests

        self.use_async_sockets = use_async_sockets
        if self.use_async_sockets:
            self.engine.process_request_outputs_callback = \
                self._async_socket_engine_callback

        self.ctx = zmq.Context()  # type: ignore[attr-defined]

        # Receive input from the client.
        self.input_socket = self.ctx.socket(zmq.constants.PULL)
        self.input_socket.bind(f"{ipc_path}{IPC_INPUT_EXT}")

        # Send output stream back to client.
        self.output_socket = self.ctx.socket(zmq.constants.PUSH)
        self.output_socket.bind(f"{ipc_path}{IPC_OUTPUT_EXT}")

        # Send heartbeats back to client.
        self.heartbeat_socket = self.ctx.socket(zmq.constants.PUSH)
        self.heartbeat_socket.bind(f"{ipc_path}{IPC_HEALTH_EXT}")

        # IPC path for the data socket.
        self.data_ipc_path = f"{ipc_path}{IPC_DATA_EXT}"

        # Error state.
        self._errored_with: Optional[BaseException] = None

    @property
    def dead_error(self) -> BaseException:
        if self._errored_with is not None:
            return ENGINE_DEAD_ERROR(self._errored_with)
        else:
            return ENGINE_DEAD_ERROR()

    @classmethod
    def from_engine_args(cls, engine_args: AsyncEngineArgs,
                         usage_context: UsageContext, ipc_path: str):
        """Creates an MQLLMEngine from the engine arguments."""
        # Setup plugins for each process
        from vllm.plugins import load_general_plugins
        load_general_plugins()

        engine_config = engine_args.create_engine_config(usage_context)
        executor_class = LLMEngine._get_executor_cls(engine_config)

        use_async_sockets = engine_config.model_config.use_async_output_proc

        return cls(ipc_path=ipc_path,
                   use_async_sockets=use_async_sockets,
                   vllm_config=engine_config,
                   executor_class=executor_class,
                   log_requests=not engine_args.disable_log_requests,
                   log_stats=not engine_args.disable_log_stats,
                   usage_context=usage_context)

    def start(self):
        try:
            try:
                logger.debug("Starting Startup Loop.")
                self.run_startup_loop()
                logger.debug("Starting Engine Loop.")
                self.run_engine_loop()
            except Exception as e:
                logger.exception(repr(e))
        except KeyboardInterrupt:
            logger.debug("Shutting down MQLLMEngine.")
        finally:
            logger.debug("MQLLMEngine is shut down.")
            self.cleanup()

    def cleanup(self):
        """Cleanup zeromq state on shutdown."""
        # Closes all sockets and destroys context.
        self.ctx.destroy(linger=0)
        del self.engine

    @contextmanager
    def make_data_socket(
            self) -> Iterator[zmq.Socket]:  # type: ignore[name-defined]
        socket = self.ctx.socket(zmq.constants.ROUTER)
        try:
            socket.bind(self.data_ipc_path)
            yield socket
        finally:
            socket.close(linger=0)

    def run_startup_loop(self) -> None:
        """Startup loop for sending data from Engine -> Client."""

        with self.make_data_socket() as socket:
            response: Union[RPCStartupResponse, BaseException]
            try:
                identity, message = socket.recv_multipart(copy=False)
                request: RPCStartupRequest = pickle.loads(message.buffer)

                # Handle the query from the Client.
                if request == RPCStartupRequest.IS_SERVER_READY:
                    tracing_enabled = self.engine.is_tracing_enabled()
                    response = RPCStartupResponse(
                        tracing_enabled=tracing_enabled)

            except Exception as e:
                response = e

            socket.send_multipart((identity, pickle.dumps(response)),
                                  copy=False)

    def run_engine_loop(self):
        """Core busy loop of the LLMEngine."""

        while True:
            if not self.engine.has_unfinished_requests():
                # Poll until there is work to do.
                while self.input_socket.poll(timeout=POLLING_TIMEOUT_MS) == 0:
                    # When there's no work, check on engine health and send
                    # health status back to client
                    self._health_check()
                    self.engine.do_log_stats()
                    logger.debug("Waiting for new requests in engine loop.")

            # Handle any input from the client.
            self.handle_new_input()

            # Engine step.
            request_outputs = self.engine_step()

            # Send request outputs (if async, done in engine_step callback).
            if not self.use_async_sockets:
                self._send_outputs(request_outputs)

    def engine_step(self) -> List[RequestOutput]:
        """Engine step wrapper with error handling."""
        try:
            return self.engine.step()
        except SystemExit:
            raise
        except BaseException as e:
            self._set_errored(e)
            rpc_err = RPCError(request_id=None,
                               is_engine_errored=True,
                               exception=e)
            self._send_outputs(rpc_err)
            raise e

    def handle_new_input(self):
        """Handle new input from the socket"""
        try:
            while self.input_socket.poll(timeout=0) != 0:
                frames = self.input_socket.recv_multipart(copy=False)
                request = pickle.loads(frames[0].buffer)

                if isinstance(request, RPCProcessRequest):
                    if len(frames) > 1:
                        # Use cloudpickle for logits processors
                        assert isinstance(request.params, SamplingParams)
                        lprocs = cloudpickle.loads(frames[1].buffer)
                        request.params.logits_processors = lprocs
                    self._handle_process_request(request)
                elif isinstance(request, RPCAbortRequest):
                    self._handle_abort_request(request)
                elif isinstance(request, RPCUProfileRequest):
                    if request == RPCUProfileRequest.START_PROFILE:
                        self.start_profile()
                    else:
                        self.stop_profile()
                elif isinstance(request, RPCLoadAdapterRequest):
                    self._handle_load_adapter_request(request)
                elif isinstance(request, RPCResetPrefixCacheRequest):
                    self.reset_prefix_cache()
                else:
                    raise ValueError("Unknown RPCRequest Type: "
                                     f"{type(request)}")

        except Exception as e:
            self._set_errored(e)
            self._send_unhealthy(e)
            raise e

    def _handle_process_request(self, request: RPCProcessRequest):
        """Handle RPCProcessRequest by adding it to the LLMEngine."""
        request_id = request.request_id

        if self._errored_with is not None:
            rpc_err = RPCError(request_id=request_id,
                               is_engine_errored=True,
                               exception=ENGINE_DEAD_ERROR(self._errored_with))
            self._send_outputs(rpc_err)

        try:
            self.engine.add_request(
                request_id=request_id,
                prompt=request.prompt,
                params=request.params,
                lora_request=request.lora_request,
                trace_headers=request.trace_headers,
                prompt_adapter_request=request.prompt_adapter_request,
                priority=request.priority)

            if self.log_requests:
                logger.info("Added request %s.", request.request_id)

        except Exception as e:
            # We do not set self._errored = True here, since the error
            # is due to an issue adding this request to the engine,
            # rather than an issue with the engine itself.
            is_errored = self._errored_with is not None
            rpc_err = RPCError(request_id=request_id,
                               is_engine_errored=is_errored,
                               exception=e)
            self._send_outputs(rpc_err)

            # Remove request from the engine.
            self.engine.abort_request(request_id)

    def _handle_abort_request(self, request: RPCAbortRequest):
        self.engine.abort_request(request.request_id)
        if self.log_requests:
            logger.info("Aborted request %s.", request.request_id)

    def _handle_load_adapter_request(self, request: RPCLoadAdapterRequest):
        try:
            self.engine.add_lora(request.lora_request)
        except BaseException as e:
            # Send back an error if the adater fails to load
            rpc_err = RPCError(request_id=request.request_id,
                               is_engine_errored=False,
                               exception=e)
            self._send_outputs(rpc_err)
            return
        # Otherwise, send back the successful load message
        self._send_outputs(
            RPCAdapterLoadedResponse(request_id=request.request_id))

    def _health_check(self):
        # Send unhealthy if engine has already errored
        if self._errored_with is not None:
            self._send_unhealthy(self._errored_with)
        try:
            self.engine.check_health()
            self._send_healthy()
        except Exception as e:
            self._set_errored(e)
            self._send_unhealthy(e)

    def _send_outputs(self, outputs: REQUEST_OUTPUTS_T):
        """Send outputs back to the engine client. These can be:
        - Exceptions
        - A list of generation outputs
        - A response from loading a lora adapter
        """
        if outputs:
            try:
                from ray.exceptions import RayTaskError

                # RayTaskError might not pickelable here. We need to unpack the
                # underlying exception as the real exception in the output.
                if (isinstance(outputs, RPCError)
                        and isinstance(outputs.exception, RayTaskError)):
                    outputs.exception = outputs.exception.cause
            except ImportError:
                pass

            output_bytes = pickle.dumps(outputs)
            self.output_socket.send_multipart((output_bytes, ), copy=False)

    def _send_healthy(self):
        """Send HEALTHY message to RPCClient."""
        if not self.heartbeat_socket.closed:
            self.heartbeat_socket.send_multipart(HEALTHY_RESPONSE, copy=False)

    def _send_unhealthy(self, error: BaseException):
        """Send UNHEALTHY message to RPCClient."""
        if not self.heartbeat_socket.closed:
            error_bytes = pickle.dumps(error)
            self.heartbeat_socket.send_multipart((error_bytes, ), copy=False)

    def _async_socket_engine_callback(self,
                                      request_outputs: REQUEST_OUTPUTS_T):
        """Callback used by engine to make socket handling async with GPU."""
        self._send_outputs(request_outputs)
        self.handle_new_input()

    def _set_errored(self, e: BaseException):
        """Log and set errored status if this is the first issue."""
        if self._errored_with is None:
            self._errored_with = e

    def start_profile(self) -> None:
        self.engine.start_profile()

    def stop_profile(self) -> None:
        self.engine.stop_profile()

    def reset_prefix_cache(self) -> bool:
        return self.engine.reset_prefix_cache()


def signal_handler(*_) -> None:
    raise KeyboardInterrupt("MQLLMEngine terminated")


def run_mp_engine(engine_args: AsyncEngineArgs, usage_context: UsageContext,
                  ipc_path: str, engine_alive):
    try:
        engine = MQLLMEngine.from_engine_args(engine_args=engine_args,
                                              usage_context=usage_context,
                                              ipc_path=ipc_path)

        signal.signal(signal.SIGTERM, signal_handler)

        engine.start()

    except BaseException as e:
        logger.exception(e)
        engine_alive.value = False
        raise e