[Feature] Support loading weights from ckpt engine worker (#11755)

Signed-off-by: Yang Kaiyong <yangkaiyong.yky@antgroup.com>
Signed-off-by: Cruz Zhao <CruzZhao@linux.alibaba.com>
Signed-off-by: Xuchun Shang <xuchun.shang@gmail.com>
Co-authored-by: Yang Kaiyong <yangkaiyong.yky@antgroup.com>
Co-authored-by: Cruz Zhao <CruzZhao@linux.alibaba.com>
Co-authored-by: Xuchun Shang <xuchun.shang@gmail.com>
Co-authored-by: Shangming Cai <csmthu@gmail.com>

docs/references/environment_variables.md

@@ -100,4 +100,5 @@ SGLang supports various environment variables that can be used to configure its
 
 | Environment Variable | Description | Default Value |
 | --- | --- | --- |
+| `SGLANG_WAIT_WEIGHTS_READY_TIMEOUT` | Timeout period for waiting on weights | `120` |
 | `SGLANG_DISABLE_OUTLINES_DISK_CACHE` | Disable Outlines disk cache | `true` |

examples/checkpoint_engine/update.py

+"""
+Usage:
+1) Launch the server with wait-for-initial-weights option in one terminal:
+   python -m sglang.launch_server --model-path /workspace/Qwen/Qwen3-4B/ --tensor-parallel-size 2 --port 19730 --load-format dummy --checkpoint-engine-wait-weights-before-ready --mem-fraction-static 0.7
+
+2) Torchrun this script in another terminal:
+    torchrun --nproc-per-node 2 update.py --update-method broadcast --checkpoint-path /workspace/Qwen/Qwen3-4B/  --inference-parallel-size 2
+"""
+
+import argparse
+import json
+import os
+import pickle
+import time
+from collections import defaultdict
+from collections.abc import Callable
+from contextlib import contextmanager
+from typing import Literal
+
+import httpx
+import torch
+import torch.distributed as dist
+from checkpoint_engine.ps import ParameterServer
+from loguru import logger
+from safetensors import safe_open
+
+
+@contextmanager
+def timer(msg: str):
+    start = time.perf_counter()
+    yield
+    end = time.perf_counter()
+    logger.info(f"{msg} duration: {end - start:.2f} seconds")
+
+
+def check_sglang_ready(
+    endpoint: str, inference_parallel_size: int, uds: str | None = None
+):
+    if rank != rank // inference_parallel_size * inference_parallel_size:
+        return
+    retry_num = 0
+    transport = None
+    if uds is not None:
+        transport = httpx.HTTPTransport(uds=uds)
+    with httpx.Client(transport=transport) as client:
+        while True:
+            try:
+                response = client.get(f"{endpoint}/ping", timeout=10)
+                response.raise_for_status()
+                break
+            except (httpx.ConnectError, httpx.HTTPStatusError) as e:
+                if retry_num % 10 == 0:
+                    logger.warning(
+                        f"fail to check sglang ready, retry {retry_num} times, error: {e}"
+                    )
+                retry_num += 1
+                time.sleep(0.1)
+
+
+def split_checkpoint_files(
+    checkpoint_path: str, rank: int, world_size: int
+) -> list[str]:
+    checkpoint_files = [
+        os.path.join(checkpoint_path, f)
+        for f in filter(
+            lambda x: x.endswith(".safetensors"), os.listdir(checkpoint_path)
+        )
+    ]
+    files_per_rank = (len(checkpoint_files) + world_size - 1) // world_size
+    return checkpoint_files[rank * files_per_rank : (rank + 1) * files_per_rank]
+
+
+def split_tensors(
+    checkpoint_path: str, rank: int, world_size: int
+) -> dict[str, torch.Tensor]:
+    index_fn = os.path.join(checkpoint_path, "model.safetensors.index.json")
+    with open(index_fn) as f:
+        weight_map: dict[str, str] = json.load(f)["weight_map"]
+    weights_per_rank = (len(weight_map) + world_size - 1) // world_size
+    fn_tensors: dict[str, list[str]] = defaultdict(list)
+    weight_keys = list(weight_map.items())
+    for name, file in weight_keys[
+        rank * weights_per_rank : (rank + 1) * weights_per_rank
+    ]:
+        fn_tensors[file].append(name)
+    named_tensors = {}
+    for file, names in fn_tensors.items():
+        with safe_open(os.path.join(checkpoint_path, file), framework="pt") as f:
+            for name in names:
+                named_tensors[name] = f.get_tensor(name)
+    return named_tensors
+
+
+def req_inference(
+    endpoint: str,
+    inference_parallel_size: int,
+    timeout: float = 300.0,
+    uds: str | None = None,
+    weight_version: str | None = None,
+) -> Callable[[list[tuple[str, str]]], None]:
+    rank = int(os.getenv("RANK", 0))
+    src = rank // inference_parallel_size * inference_parallel_size
+
+    def req_func(socket_paths: list[tuple[str, str]]):
+        if rank == src:
+            with httpx.Client(transport=httpx.HTTPTransport(uds=uds)) as client:
+                resp = client.post(
+                    f"{endpoint}/update_weights_from_ipc",
+                    json={
+                        "zmq_handles": dict(
+                            socket_paths[src : src + inference_parallel_size]
+                        ),
+                        "flush_cache": True,
+                        "weight_version": weight_version,
+                    },
+                    timeout=timeout,
+                )
+                resp.raise_for_status()
+
+    return req_func
+
+
+def update_weights(
+    ps: ParameterServer,
+    checkpoint_name: str,
+    checkpoint_files: list[str],
+    named_tensors: dict[str, torch.Tensor],
+    req_func: Callable[[list[tuple[str, str]]], None],
+    inference_parallel_size: int,
+    endpoint: str,
+    save_metas_file: str | None = None,
+    update_method: Literal["broadcast", "p2p", "all"] = "broadcast",
+    uds: str | None = None,
+):
+    ps.register_checkpoint(
+        checkpoint_name, files=checkpoint_files, named_tensors=named_tensors
+    )
+    ps.init_process_group()
+    check_sglang_ready(endpoint, inference_parallel_size, uds)
+    dist.barrier()
+    with timer("Gather metas"):
+        ps.gather_metas(checkpoint_name)
+    if save_metas_file and int(os.getenv("RANK")) == 0:
+        with open(save_metas_file, "wb") as f:
+            pickle.dump(ps.get_metas(), f)
+
+    if update_method == "broadcast" or update_method == "all":
+        with timer("Update weights without setting ranks"):
+            ps.update(checkpoint_name, req_func)
+
+    if update_method == "p2p" or update_method == "all":
+        if update_method:
+            # sleep 2s to wait destroy process group
+            time.sleep(2)
+        with timer("Update weights with setting ranks"):
+            ps.update(
+                checkpoint_name, req_func, ranks=list(range(inference_parallel_size))
+            )
+
+
+def join(
+    ps: ParameterServer,
+    checkpoint_name: str,
+    load_metas_file: str,
+    req_func: Callable[[list[tuple[str, str]]], None],
+    inference_parallel_size: int,
+    endpoint: str,
+    uds: str | None = None,
+):
+    assert load_metas_file, "load_metas_file is required"
+    with open(load_metas_file, "rb") as f:
+        metas = pickle.load(f)
+    ps.init_process_group()
+    check_sglang_ready(endpoint, inference_parallel_size, uds)
+    dist.barrier()
+    with timer("Gather metas before join"):
+        ps.gather_metas(checkpoint_name)
+    ps.load_metas(metas)
+    with timer(
+        f"Update weights with setting ranks as range(0, {inference_parallel_size}) by using p2p"
+    ):
+        ps.update(checkpoint_name, req_func, ranks=list(range(inference_parallel_size)))
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="Update weights example")
+    parser.add_argument("--checkpoint-path", type=str, default=None)
+    parser.add_argument("--save-metas-file", type=str, default=None)
+    parser.add_argument("--load-metas-file", type=str, default=None)
+    parser.add_argument("--sleep-time", type=int, default=0)
+    parser.add_argument("--endpoint", type=str, default="http://localhost:19730")
+    parser.add_argument("--inference-parallel-size", type=int, default=8)
+    parser.add_argument("--checkpoint-name", type=str, default="my-checkpoint-iter-0")
+    parser.add_argument("--update-method", type=str, default="broadcast")
+    parser.add_argument("--uds", type=str, default=None)
+    parser.add_argument("--weight-version", type=str, default=None)
+    args = parser.parse_args()
+    rank = int(os.getenv("RANK"))
+    world_size = int(os.getenv("WORLD_SIZE"))
+    req_func = req_inference(
+        args.endpoint,
+        args.inference_parallel_size,
+        uds=args.uds,
+        weight_version=args.weight_version,
+    )
+    ps = ParameterServer(auto_pg=True)
+    ps._p2p_store = None
+    if args.load_metas_file:
+        join(
+            ps,
+            args.checkpoint_name,
+            args.load_metas_file,
+            req_func,
+            args.inference_parallel_size,
+            args.endpoint,
+            args.uds,
+        )
+    else:
+        if os.path.exists(
+            os.path.join(args.checkpoint_path, "model.safetensors.index.json")
+        ):
+            named_tensors = split_tensors(args.checkpoint_path, rank, world_size)
+            checkpoint_files = []
+        else:
+            checkpoint_files = split_checkpoint_files(
+                args.checkpoint_path, rank, world_size
+            )
+            named_tensors = {}
+        update_weights(
+            ps,
+            args.checkpoint_name,
+            checkpoint_files,
+            named_tensors,
+            req_func,
+            args.inference_parallel_size,
+            args.endpoint,
+            args.save_metas_file,
+            args.update_method,
+            args.uds,
+        )
+    time.sleep(args.sleep_time)

python/pyproject.toml

@@ -89,6 +89,7 @@ test = [
   "sentence_transformers",
   "tabulate",
 ]
+checkpoint-engine = ["checkpoint-engine==0.1.2"]
 all = []
 dev = ["sglang[test]"]
 

python/sglang/srt/checkpoint_engine/checkpoint_engine_worker.py

+# Copyright 2023-2024 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.
+# ==============================================================================
+"""
+Checkpoint-engine integration for SGLang.
+This module provides weight update functionality via IPC for checkpoint-engine compatibility.
+"""
+import logging
+from typing import Callable, Dict, Optional
+
+import torch
+import zmq
+
+try:
+    from checkpoint_engine.worker import update_weights_from_ipc
+except ImportError:
+    raise ImportError(
+        "checkpoint-engine is not installed. "
+        "Please install it with: pip install sglang[checkpoint-engine]"
+    )
+
+logger = logging.getLogger(__name__)
+
+
+class SGLangCheckpointEngineWorkerExtension:
+    """
+    Worker extension for SGLang to support checkpoint-engine IPC weight updates.
+    This class provides the interface needed for checkpoint-engine integration.
+    """
+
+    def __init__(self):
+        self._zmq_ctx: Optional[zmq.Context] = None
+
+    def get_device_uuid(self) -> str:
+        """Get the UUID of current device."""
+        # We need to implement this to get the device UUID
+        # This will be overridden when integrated into SGLang's worker
+        raise NotImplementedError(
+            "This method should be overridden by SGLang integration"
+        )
+
+    def get_device_id(self) -> int:
+        """Get the device ID."""
+        raise NotImplementedError(
+            "This method should be overridden by SGLang integration"
+        )
+
+    def get_model_loader(self) -> Callable:
+        """Get the model weight loader function."""
+        raise NotImplementedError(
+            "This method should be overridden by SGLang integration"
+        )
+
+    def get_post_hook(self) -> Optional[Callable]:
+        """Get the post-processing hook after weight loading."""
+        return None
+
+    def update_weights_from_ipc(self, zmq_handles: Dict[str, str]):
+        """
+        Update weights from IPC communication.
+        Args:
+            zmq_handles: Dict mapping device UUID to ZMQ socket path
+        """
+        if self._zmq_ctx is None:
+            self._zmq_ctx = zmq.Context()
+        device_uuid = self.get_device_uuid()
+        device_id = self.get_device_id()
+        if device_uuid not in zmq_handles:
+            raise ValueError(
+                f"Device UUID {device_uuid} not found in zmq_handles: {list(zmq_handles.keys())}"
+            )
+        update_weights_from_ipc(
+            self._zmq_ctx,
+            zmq_handles[device_uuid],
+            device_id=device_id,
+            run=self.get_model_loader(),
+            post_hook=self.get_post_hook(),
+        )
+
+
+class SGLangCheckpointEngineWorkerExtensionImpl(SGLangCheckpointEngineWorkerExtension):
+    """
+    Implementation of SGLangCheckpointEngineWorkerExtension that integrates with SGLang's model runner.
+    This class provides the concrete implementation for checkpoint-engine IPC weight updates.
+    """
+
+    def __init__(self, model_runner):
+        super().__init__()
+        self.model_runner = model_runner
+
+    def get_device_uuid(self) -> str:
+        """Get the UUID of current device."""
+        # Get device UUID for current device
+        device_id = torch.cuda.current_device()
+        try:
+            return f"GPU-{torch.cuda.get_device_properties(device_id).uuid!s}"
+        except AssertionError as e:
+            raise ValueError(f"Failed to get GPU UUID for device {device_id}") from e
+
+    def get_device_id(self) -> int:
+        """Get the device ID."""
+        return torch.cuda.current_device()
+
+    def get_model_loader(self) -> Callable:
+        """Get the model weight loader function."""
+        return self.model_runner.model.load_weights
+
+    def get_post_hook(self) -> Optional[Callable]:
+        """Get the post-processing hook after weight loading."""
+
+        def post_hook():
+            # Perform post-processing after weight loading similar to DefaultModelLoader
+            try:
+                from sglang.srt.model_loader.loader import device_loading_context
+
+                # Process quantization methods after loading weights
+                for _, module in self.model_runner.model.named_modules():
+                    quant_method = getattr(module, "quant_method", None)
+                    if quant_method is not None:
+                        # Move parameters to device if needed for quantization processing
+                        target_device = torch.device(
+                            "cuda", torch.cuda.current_device()
+                        )
+                        with device_loading_context(module, target_device):
+                            quant_method.process_weights_after_loading(module)
+                # Call model-specific post-loading hook if available
+                if hasattr(self.model_runner.model, "post_load_weights"):
+                    self.model_runner.model.post_load_weights()
+            except Exception as e:
+                logger.warning(f"Post-hook processing failed: {e}")
+
+        return post_hook

python/sglang/srt/entrypoints/engine.py

@@ -59,6 +59,7 @@ from sglang.srt.managers.io_struct import (
     UnloadLoRAAdapterReqInput,
     UpdateWeightFromDiskReqInput,
     UpdateWeightsFromDistributedReqInput,
+    UpdateWeightsFromIPCReqInput,
     UpdateWeightsFromTensorReqInput,
 )
 from sglang.srt.managers.multi_tokenizer_mixin import MultiTokenizerRouter
@@ -649,6 +650,21 @@ class Engine(EngineBase):
             request=None,
         )
 
+    def update_weights_from_ipc(
+        self,
+        zmq_handles: Dict[str, str],
+        flush_cache: bool = True,
+    ):
+        """Update weights from IPC for checkpoint-engine integration."""
+        obj = UpdateWeightsFromIPCReqInput(
+            zmq_handles=zmq_handles,
+            flush_cache=flush_cache,
+        )
+        loop = asyncio.get_event_loop()
+        return loop.run_until_complete(
+            self.tokenizer_manager.update_weights_from_ipc(obj, None)
+        )
+
 
 def _set_envs_and_config(server_args: ServerArgs):
     # Set global environments

python/sglang/srt/entrypoints/http_server.py

@@ -96,6 +96,7 @@ from sglang.srt.managers.io_struct import (
     UnloadLoRAAdapterReqInput,
     UpdateWeightFromDiskReqInput,
     UpdateWeightsFromDistributedReqInput,
+    UpdateWeightsFromIPCReqInput,
     UpdateWeightsFromTensorReqInput,
     UpdateWeightVersionReqInput,
     VertexGenerateReqInput,
@@ -129,6 +130,7 @@ logger = logging.getLogger(__name__)
 asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
 
 HEALTH_CHECK_TIMEOUT = int(os.getenv("SGLANG_HEALTH_CHECK_TIMEOUT", 20))
+WAIT_WEIGHTS_READY_TIMEOUT = int(os.getenv("SGLANG_WAIT_WEIGHTS_READY_TIMEOUT", 120))
 
 
 # Store global states
@@ -838,6 +840,27 @@ async def update_weights_from_distributed(
         return ORJSONResponse(content, status_code=HTTPStatus.BAD_REQUEST)
 
 
+@app.post("/update_weights_from_ipc")
+async def update_weights_from_ipc(obj: UpdateWeightsFromIPCReqInput, request: Request):
+    """Update the weights from IPC (Inter-Process Communication) for checkpoint-engine integration."""
+    success, message = await _global_state.tokenizer_manager.update_weights_from_ipc(
+        obj, request
+    )
+
+    # Update weight version if provided and weights update was successful
+    if success and obj.weight_version is not None:
+        _update_weight_version_if_provided(obj.weight_version)
+        message += f" Weight version updated to {obj.weight_version}."
+
+    content = {"success": success, "message": message}
+    if success:
+        if _global_state.tokenizer_manager.initial_weights_loaded is False:
+            _global_state.tokenizer_manager.initial_weights_loaded = True
+        return ORJSONResponse(content)
+    else:
+        return ORJSONResponse(content, status_code=HTTPStatus.BAD_REQUEST)
+
+
 @app.post("/update_weight_version")
 async def update_weight_version(obj: UpdateWeightVersionReqInput, request: Request):
     """Update the weight version. This operation requires no active requests."""
@@ -1530,6 +1553,8 @@ def _wait_and_warmup(
     pipe_finish_writer: Optional[multiprocessing.connection.Connection],
     launch_callback: Optional[Callable[[], None]] = None,
 ):
+    if server_args.checkpoint_engine_wait_weights_before_ready:
+        _wait_weights_ready()
     if not server_args.skip_server_warmup:
         if not _execute_server_warmup(
             server_args,
@@ -1552,3 +1577,24 @@ def _wait_and_warmup(
 
     if launch_callback is not None:
         launch_callback()
+
+
+def _wait_weights_ready():
+    """Wait for weights to be ready within the specified timeout."""
+    timeout = WAIT_WEIGHTS_READY_TIMEOUT
+    start_time = time.time()
+
+    for _ in range(timeout):
+        if _global_state.tokenizer_manager.initial_weights_loaded:
+            logger.info(
+                f"Weights are ready after {time.time() - start_time:.2f} seconds"
+            )
+            return
+        time.sleep(1)
+
+    # Timeout reached without weights being ready
+    logger.error(
+        f"Weights are not ready after waiting {timeout} seconds. "
+        f"Consider increasing SGLANG_WAIT_WEIGHTS_READY_TIMEOUT environment variable. "
+        f"Current status: initial_weights_loaded={_global_state.tokenizer_manager.initial_weights_loaded}"
+    )

python/sglang/srt/managers/io_struct.py

@@ -1080,6 +1080,24 @@ class InitWeightsSendGroupForRemoteInstanceReqInput(BaseReq):
     backend: str = "nccl"
 
 
+# Now UpdateWeightsFromIPCReqInput and UpdateWeightsFromIPCReqOutput
+# are only used by Checkpoint Engine (https://github.com/MoonshotAI/checkpoint-engine)
+@dataclass
+class UpdateWeightsFromIPCReqInput(BaseReq):
+    # ZMQ socket paths for each device UUID
+    zmq_handles: Dict[str, str]
+    # Whether to flush cache after weight update
+    flush_cache: bool = True
+    # Optional: Update weight version along with weights
+    weight_version: Optional[str] = None
+
+
+@dataclass
+class UpdateWeightsFromIPCReqOutput(BaseReq):
+    success: bool
+    message: str
+
+
 @dataclass
 class InitWeightsSendGroupForRemoteInstanceReqOutput(BaseReq):
     success: bool

python/sglang/srt/managers/scheduler.py

@@ -109,6 +109,7 @@ from sglang.srt.managers.io_struct import (
     UnloadLoRAAdapterReqOutput,
     UpdateWeightFromDiskReqInput,
     UpdateWeightsFromDistributedReqInput,
+    UpdateWeightsFromIPCReqInput,
     UpdateWeightsFromTensorReqInput,
 )
 from sglang.srt.managers.mm_utils import init_embedding_cache
@@ -530,6 +531,7 @@ class Scheduler(
                     self.update_weights_from_distributed,
                 ),
                 (UpdateWeightsFromTensorReqInput, self.update_weights_from_tensor),
+                (UpdateWeightsFromIPCReqInput, self.update_weights_from_ipc),
                 (GetWeightsByNameReqInput, self.get_weights_by_name),
                 (ReleaseMemoryOccupationReqInput, self.release_memory_occupation),
                 (ResumeMemoryOccupationReqInput, self.resume_memory_occupation),

python/sglang/srt/managers/scheduler_update_weights_mixin.py

@@ -21,6 +21,8 @@ from sglang.srt.managers.io_struct import (
     UpdateWeightFromDiskReqOutput,
     UpdateWeightsFromDistributedReqInput,
     UpdateWeightsFromDistributedReqOutput,
+    UpdateWeightsFromIPCReqInput,
+    UpdateWeightsFromIPCReqOutput,
     UpdateWeightsFromTensorReqInput,
     UpdateWeightsFromTensorReqOutput,
 )
@@ -80,6 +82,18 @@ class SchedulerUpdateWeightsMixin:
         torch.distributed.barrier(group=self.tp_cpu_group)
         return UpdateWeightsFromTensorReqOutput(success, message)
 
+    def update_weights_from_ipc(self, recv_req: UpdateWeightsFromIPCReqInput):
+        """Update the online model parameter from IPC for checkpoint-engine integration."""
+        success, message = self.tp_worker.update_weights_from_ipc(recv_req)
+        if success:
+            if recv_req.flush_cache:
+                flush_cache_success = self.flush_cache()
+                assert flush_cache_success, "Cache flush failed after updating weights"
+        else:
+            logger.error(message)
+        torch.distributed.barrier(group=self.tp_cpu_group)
+        return UpdateWeightsFromIPCReqOutput(success, message)
+
     def get_weights_by_name(self, recv_req: GetWeightsByNameReqInput):
         parameter = self.tp_worker.get_weights_by_name(recv_req)
         return GetWeightsByNameReqOutput(parameter)

python/sglang/srt/managers/tokenizer_communicator_mixin.py

@@ -63,6 +63,8 @@ from sglang.srt.managers.io_struct import (
     UnloadLoRAAdapterReqOutput,
     UpdateWeightsFromDistributedReqInput,
     UpdateWeightsFromDistributedReqOutput,
+    UpdateWeightsFromIPCReqInput,
+    UpdateWeightsFromIPCReqOutput,
     UpdateWeightsFromTensorReqInput,
     UpdateWeightsFromTensorReqOutput,
 )
@@ -169,6 +171,9 @@ class TokenizerCommunicatorMixin:
         self.update_weights_from_tensor_communicator = _Communicator(
             self.send_to_scheduler, server_args.dp_size
         )
+        self.update_weights_from_ipc_communicator = _Communicator(
+            self.send_to_scheduler, server_args.dp_size
+        )
         self.get_weights_by_name_communicator = _Communicator(
             self.send_to_scheduler, server_args.dp_size
         )
@@ -235,6 +240,10 @@ class TokenizerCommunicatorMixin:
                     UpdateWeightsFromTensorReqOutput,
                     self.update_weights_from_tensor_communicator.handle_recv,
                 ),
+                (
+                    UpdateWeightsFromIPCReqOutput,
+                    self.update_weights_from_ipc_communicator.handle_recv,
+                ),
                 (
                     GetWeightsByNameReqOutput,
                     self.get_weights_by_name_communicator.handle_recv,
@@ -442,6 +451,28 @@ class TokenizerCommunicatorMixin:
             result = (await self.update_weights_from_tensor_communicator(obj))[0]
             return result.success, result.message
 
+    async def update_weights_from_ipc(
+        self,
+        obj: UpdateWeightsFromIPCReqInput,
+        request: Optional[fastapi.Request] = None,
+    ) -> Tuple[bool, str]:
+        """Update weights via IPC for checkpoint-engine integration."""
+        self.auto_create_handle_loop()
+        try:
+            # For now, we only support single data parallel instance
+            assert (
+                self.server_args.dp_size == 1 or self.server_args.enable_dp_attention
+            ), "dp_size must be 1 or dp attention must be enabled for update weights from IPC"
+            logger.info("Starting IPC weight update")
+            # This means that weight sync cannot run while requests are in progress.
+            async with self.model_update_lock.writer_lock:
+                result = (await self.update_weights_from_ipc_communicator(obj))[0]
+                return result.success, result.message
+        except Exception as e:
+            error_msg = f"IPC weight update failed: {str(e)}"
+            logger.error(error_msg)
+            return False, error_msg
+
     async def load_lora_adapter(
         self: TokenizerManager,
         obj: LoadLoRAAdapterReqInput,

python/sglang/srt/managers/tokenizer_manager.py

@@ -284,6 +284,11 @@ class TokenizerManager(TokenizerCommunicatorMixin):
         self.gracefully_exit = False
         self.last_receive_tstamp = 0
 
+        # Initial weights status
+        self.initial_weights_loaded = True
+        if server_args.checkpoint_engine_wait_weights_before_ready:
+            self.initial_weights_loaded = False
+
         # Dumping
         self.dump_requests_folder = ""  # By default do not dump
         self.dump_requests_threshold = 1000

python/sglang/srt/managers/tp_worker.py

@@ -32,6 +32,7 @@ from sglang.srt.managers.io_struct import (
     UnloadLoRAAdapterReqInput,
     UpdateWeightFromDiskReqInput,
     UpdateWeightsFromDistributedReqInput,
+    UpdateWeightsFromIPCReqInput,
     UpdateWeightsFromTensorReqInput,
 )
 from sglang.srt.managers.schedule_batch import ModelWorkerBatch
@@ -164,6 +165,11 @@ class BaseTpWorker(ABC):
         )
         return success, message
 
+    def update_weights_from_ipc(self, recv_req: UpdateWeightsFromIPCReqInput):
+        """Update weights from IPC for checkpoint-engine integration."""
+        success, message = self.model_runner.update_weights_from_ipc(recv_req)
+        return success, message
+
     def get_weights_by_name(self, recv_req: GetWeightsByNameReqInput):
         parameter = self.model_runner.get_weights_by_name(
             recv_req.name, recv_req.truncate_size

python/sglang/srt/model_executor/model_runner.py

@@ -2387,6 +2387,23 @@ class ModelRunner:
         )
         ShardedStateLoader.save_model(self.model, path, pattern, max_size)
 
+    def update_weights_from_ipc(self, recv_req):
+        """Update weights from IPC for checkpoint-engine integration."""
+        try:
+            from sglang.srt.checkpoint_engine.checkpoint_engine_worker import (
+                SGLangCheckpointEngineWorkerExtensionImpl,
+            )
+
+            # Create a worker extension that integrates with SGLang's model
+            worker = SGLangCheckpointEngineWorkerExtensionImpl(self)
+            worker.update_weights_from_ipc(recv_req.zmq_handles)
+            return True, "IPC weight update completed successfully"
+        except ImportError as e:
+            return False, f"IPC weight update failed: ImportError {e}"
+        except Exception as e:
+            logger.error(f"IPC weight update failed: {e}")
+            return False, str(e)
+
 
 def _model_load_weights_direct(model, named_tensors: List[Tuple[str, torch.Tensor]]):
     params_dict = dict(model.named_parameters())

python/sglang/srt/server_args.py

@@ -208,6 +208,7 @@ class ServerArgs:
     skip_server_warmup: bool = False
     warmups: Optional[str] = None
     nccl_port: Optional[int] = None
+    checkpoint_engine_wait_weights_before_ready: bool = False
 
     # Quantization and data type
     dtype: str = "auto"
@@ -1704,6 +1705,12 @@ class ServerArgs:
             default=ServerArgs.nccl_port,
             help="The port for NCCL distributed environment setup. Defaults to a random port.",
         )
+        parser.add_argument(
+            "--checkpoint-engine-wait-weights-before-ready",
+            action="store_true",
+            help="If set, the server will wait for initial weights to be loaded via checkpoint-engine or other update methods "
+            "before serving inference requests.",
+        )
 
         # Quantization and data type
         parser.add_argument(

python/sglang/srt/utils/common.py

@@ -2275,6 +2275,11 @@ def launch_dummy_health_check_server(host, port, enable_metrics):
 
     app = FastAPI()
 
+    @app.get("/ping")
+    async def ping():
+        """Could be used by the checkpoint-engine update script to confirm the server is up."""
+        return Response(status_code=200)
+
     @app.get("/health")
     async def health():
         """Check the health of the http server."""