sglang/python/sglang/srt/disaggregation/kv_events.py

"""
Copyright 2025 SGLang Team
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""

"""
KV caching events
"""

import atexit
import logging
import queue
import threading
import time
from abc import ABC, abstractmethod
from collections import deque
from itertools import count
from queue import Queue
from typing import Any, Callable, Optional, Union

import msgspec
import zmq
from pydantic import BaseModel

logger = logging.getLogger(__name__)


class EventBatch(
    msgspec.Struct,
    array_like=True,  # type: ignore[call-arg]
    omit_defaults=True,  # type: ignore[call-arg]
    gc=False,  # type: ignore[call-arg]
):
    ts: float
    events: list[Any]
    attn_dp_rank: Optional[int] = None


class KVCacheEvent(
    msgspec.Struct,
    array_like=True,  # type: ignore[call-arg]
    omit_defaults=True,  # type: ignore[call-arg]
    gc=False,  # type: ignore[call-arg]
    tag=True,
):
    """Base class for all KV cache-related events"""


class BlockStored(KVCacheEvent):
    block_hashes: list[int]
    parent_block_hash: Optional[int]
    token_ids: list[int]
    block_size: int
    lora_id: Optional[int]


class BlockRemoved(KVCacheEvent):
    block_hashes: list[int]


class AllBlocksCleared(KVCacheEvent):
    pass


class KVEventBatch(EventBatch):
    events: list[Union[BlockStored, BlockRemoved, AllBlocksCleared]]


class EventPublisher(ABC):
    """
    Lightweight publisher for EventBatch batches with
    support for DP attention.

    In DP attention - each rank has its own Scheduler and
    KV cache instance in order to avoid duplicate events
    and ensure proper event attribution. In our implementation

    - Each DP rank has its own EventPublisher
    - Publishers annotate events with the dp rank
    - This allows consumers to distinguish events from different DP ranks
    """

    def __init__(self, attn_dp_rank: int = 0):
        self._attn_dp_rank = attn_dp_rank

    @abstractmethod
    def publish(self, events: EventBatch) -> None:
        """Emit events in order.

        Implementations should guarantee at-least-once delivery and
        monotonic ordering (e.g., via sequence numbers).
        """

    @abstractmethod
    def shutdown(self) -> None:
        """Shutdown the publisher."""


class NullEventPublisher(EventPublisher):
    """No-op implementation (default when disabled)."""

    def publish(self, events) -> None:
        return

    def shutdown(self) -> None:
        return


class ZmqEventPublisher(EventPublisher):
    """Reliable PUB/ROUTER publisher with an in-memory replay buffer.

    Spawns a separate thread to handle publishing from a queue.

    Parameters
    ----------
    endpoint:
        PUB address. Use ``tcp://*:5557`` to bind or ``tcp://host:5557`` to
        connect.
    replay_endpoint:
        Optional ROUTER address for replay requests. When given, subscribers can
        request missed batches by sending the starting sequence number as an
        8-byte big-endian integer.
    buffer_steps:
        Number of past batches to keep for replay.
    hwm:
        ZeroMQ high-water-mark for PUB socket.
    max_queue_size:
        Maximum number of events to buffer in memory.
    topic:
        Topic to publish events to.
    """

    SHUTDOWN_TIMEOUT: float = 1.0
    END_SEQ = (-1).to_bytes(8, "big", signed=True)

    def __init__(
        self,
        attn_dp_rank: int,
        endpoint: str = "tcp://*:5557",
        replay_endpoint: Optional[str] = None,
        buffer_steps: int = 10_000,
        hwm: int = 100_000,
        max_queue_size: int = 100_000,
        topic: str = "",
    ) -> None:
        # Storage
        super().__init__(attn_dp_rank)
        self._event_queue = Queue[Optional[EventBatch]](maxsize=max_queue_size)
        self._buffer = deque[tuple[int, bytes]](maxlen=buffer_steps)

        # ZMQ sockets
        self._ctx = zmq.Context.instance()
        self._pub: Optional[zmq.Socket] = None
        self._replay: Optional[zmq.Socket] = None
        self._dp_rank = attn_dp_rank
        self._endpoint = self.offset_endpoint_port(endpoint, self._dp_rank)
        self._replay_endpoint = self.offset_endpoint_port(
            replay_endpoint, self._dp_rank
        )
        self._hwm = hwm
        self._socket_setup()

        # Payload
        self._seq_gen = count()
        self._topic_bytes = topic.encode("utf-8")

        # Thread
        self._running = True
        logger.info("Starting ZMQ publisher thread")

        self._thread = threading.Thread(
            target=self._publisher_thread, daemon=True, name="zmq-publisher"
        )
        self._thread.start()

        atexit.register(self.shutdown)

    def publish(self, events: EventBatch) -> None:
        if not self._running:
            raise RuntimeError("Publisher is closed")
        if events.attn_dp_rank is None:
            events.attn_dp_rank = self._dp_rank
        self._event_queue.put(events)

    def shutdown(self) -> None:
        """Stop the publisher thread and clean up resources."""
        self._running = False
        self._event_queue.put_nowait(None)

        start = time.time()
        pending_items = True
        while pending_items and (time.time() - start < self.SHUTDOWN_TIMEOUT):
            pending_items = not self._event_queue.empty()
            if pending_items:
                time.sleep(0.1)

        if pending_items:
            logger.warning(
                "Warning: Queue still has %s items after %s seconds timeout",
                self._event_queue.qsize(),
                self.SHUTDOWN_TIMEOUT,
            )

        if self._thread.is_alive():
            self._thread.join(timeout=self.SHUTDOWN_TIMEOUT)

        # Clean up ZMQ resources
        try:
            if self._pub is not None:
                self._pub.close(linger=0)
            if self._replay is not None:
                self._replay.close(linger=0)
        finally:
            pass  # Do not terminate context; other sockets may use it

    def _socket_setup(self) -> None:
        """Initialize sockets
        https://pyzmq.readthedocs.io/en/v19.0.0/morethanbindings.html#thread-safety
        """
        if self._pub is None:
            self._pub = self._ctx.socket(zmq.PUB)
            self._pub.set_hwm(self._hwm)
            # Heuristic: bind if wildcard / * present, else connect.
            # bind stable, connect volatile convention
            if (
                "*" in self._endpoint
                or "::" in self._endpoint
                or self._endpoint.startswith("ipc://")
                or self._endpoint.startswith("inproc://")
            ):
                self._pub.bind(self._endpoint)
            else:
                self._pub.connect(self._endpoint)

        # Set up replay socket: use ROUTER
        # 1) handles multiple REQ clients (identities)
        # 2) lets us send back one request → many replies (streamed events)
        # 3) works in our non‑blocking poll loop alongside PUB
        if self._replay_endpoint is not None:
            self._replay = self._ctx.socket(zmq.ROUTER)
            self._replay.bind(self._replay_endpoint)

    def _publisher_thread(self) -> None:
        """Background thread that processes the event queue."""
        self._pack = msgspec.msgpack.Encoder()

        assert self._pub is not None  # narrows type for mypy

        while self._running or self._event_queue.qsize() > 0:
            # --- replay (non-critical) ---------------------------------
            if self._replay is not None and self._replay.poll(0):
                try:
                    self._service_replay()
                except Exception as e:
                    logger.exception("Error in replay: %s", e)

            # --- main queue (critical) ---------------------------------
            try:
                event = self._event_queue.get(timeout=0.1)
                if event is None:
                    break  # Sentinel received, exit thread
            except queue.Empty:
                continue

            try:
                seq = next(self._seq_gen)

                payload = self._pack.encode(event)
                seq_bytes = seq.to_bytes(8, "big")
                self._pub.send_multipart((self._topic_bytes, seq_bytes, payload))

                self._buffer.append((seq, payload))
                self._event_queue.task_done()

            except Exception as e:
                # Publishing failed;  back-off a bit to avoid a tight error loop
                logger.exception("Error in publisher thread: %s", e)
                time.sleep(0.1)

    def _service_replay(self) -> None:
        """If a replay request is waiting, send buffered batches."""
        assert self._replay is not None  # narrows type for mypy

        frame = self._replay.recv_multipart()
        if len(frame) != 3:
            logger.warning("Invalid replay request: %s", frame)
            return
        client_id, _, start_seq_bytes = frame
        start_seq = int.from_bytes(start_seq_bytes, "big")

        for seq, buf in self._buffer:
            if seq >= start_seq:
                # [identity, empty_delim, seq_bytes, payload]
                # (identity, empty_delim) are stripped off by the router
                # receiving payload is (seq_bytes, payload)
                self._replay.send_multipart(
                    (client_id, b"", seq.to_bytes(8, "big"), buf)
                )
        # Send end of sequence marker
        # receiving payload is (-1, b""")
        self._replay.send_multipart((client_id, b"", self.END_SEQ, b""))

    @staticmethod
    def offset_endpoint_port(
        endpoint: Optional[str], data_parallel_rank: int
    ) -> Optional[str]:
        """Helper function to offset the port in an endpoint by
            the data parallel rank.

        Args:
            endpoint: The endpoint string
                (e.g., "tcp://*:5557" or "inproc://cache")
            data_parallel_rank: The data parallel rank to offset by

        Returns:
            The endpoint with the port offset by data_parallel_rank
                or suffix appended
        """
        # Do nothing if input is None or data_parallel_rank is 0
        if not endpoint or data_parallel_rank == 0:
            return endpoint

        if "inproc" in endpoint:
            return f"{endpoint}_dp{data_parallel_rank}"
        if "tcp" in endpoint:
            if endpoint and ":" in endpoint:
                # Get everything after the last colon (the port)
                last_colon_idx = endpoint.rfind(":")
                base_addr = endpoint[:last_colon_idx]
                base_port = int(endpoint[last_colon_idx + 1 :])
                new_port = base_port + data_parallel_rank
                return f"{base_addr}:{new_port}"
            return endpoint
        raise ValueError("Invalid endpoint: must contain 'inproc' or 'tcp'")


class KVEventsConfig(BaseModel):
    """Configuration for KV event publishing."""

    publisher: str = "null"
    """The publisher to use for publishing kv events. Can be "null", "zmq".
    """

    endpoint: str = "tcp://*:5557"
    """The zmq endpoint to use for publishing kv events.
    """

    replay_endpoint: Optional[str] = None
    """The zmq endpoint to use for replaying kv events.
    """

    buffer_steps: int = 10_000
    """The number of steps to cache for replay endpoint. Will only save
    events from the last N steps for the replay endpoint.
    """

    hwm: int = 100_000
    """The zmq high water mark for the event publisher. After queueing N events,
    events will start dropping if the consumer is not keeping up.
    """

    max_queue_size: int = 100_000
    """The maximum number of events to queue while waiting for publishing.
    """

    topic: str = ""
    """The topic to use for the event publisher. Consumers can subscribe to
    this topic to receive events.
    """

    @classmethod
    def from_cli(cls, cli_value: str) -> "KVEventsConfig":
        """Parse the CLI value for the event publisher config."""
        return KVEventsConfig.model_validate_json(cli_value)


class EventPublisherFactory:
    _registry: dict[str, Callable[..., EventPublisher]] = {
        "null": NullEventPublisher,
        "zmq": ZmqEventPublisher,
    }

    @classmethod
    def register_publisher(cls, name: str, ctor: Callable[..., EventPublisher]) -> None:
        if name in cls._registry:
            raise KeyError(f"publisher '{name}' already registered")
        cls._registry[name] = ctor

    @classmethod
    def create(cls, config: Optional[str], attn_dp_rank: int = 0) -> EventPublisher:
        """Create publisher from a config mapping."""
        if not config:
            return NullEventPublisher()
        config = KVEventsConfig.from_cli(config)
        config_dict = config.model_dump()

        kind = config_dict.pop("publisher", "null")
        try:
            constructor = cls._registry[kind]
        except KeyError as exc:
            raise ValueError(f"Unknown event publisher '{kind}'") from exc
        return constructor(attn_dp_rank=attn_dp_rank, **config_dict)