lightseekorg--tokenspeed/python/tokenspeed/runtime/distributed/device_communicators/utils.py

# SPDX-License-Identifier: MIT AND Apache-2.0
# SPDX-FileCopyrightText: Copyright (c) 2026 LightSeek Foundation
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
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# Copyright (c) 2026 LightSeek Foundation
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"""Distributed process-group helper utilities."""

import contextlib
from multiprocessing import shared_memory
from unittest.mock import patch

import torch
import torch.distributed
from torch.distributed import ProcessGroup

from tokenspeed.runtime.utils import get_colorful_logger

logger = get_colorful_logger(__name__)


def _ignore_resource_tracker_register(*args, **kwargs) -> None:
    return None


def in_the_same_node_as(pg: ProcessGroup, source_rank: int = 0) -> list[bool]:
    """
    This is a collective operation that returns if each rank is in the same node
    as the source rank. It tests if processes are attached to the same
    memory system (shared access to shared memory).
    """
    if torch.distributed.get_backend(pg) == torch.distributed.Backend.NCCL:
        raise ValueError("in_the_same_node_as should be tested with a non-NCCL group.")
    # local rank inside the group
    rank = torch.distributed.get_rank(group=pg)
    world_size = torch.distributed.get_world_size(group=pg)

    # local tensor in each process to store the result
    is_in_the_same_node = torch.tensor([0] * world_size, dtype=torch.int32)

    # global ranks of the processes in the group
    ranks = torch.distributed.get_process_group_ranks(pg)

    magic_message = b"magic_message"
    shm = None

    try:
        with contextlib.suppress(OSError):
            if rank == source_rank:
                # create a shared memory segment
                shm = shared_memory.SharedMemory(create=True, size=128)
                shm.buf[: len(magic_message)] = magic_message
                torch.distributed.broadcast_object_list(
                    [shm.name], src=ranks[source_rank], group=pg
                )
                is_in_the_same_node[rank] = 1
            else:
                # try to open the shared memory segment
                recv = [None]
                torch.distributed.broadcast_object_list(
                    recv, src=ranks[source_rank], group=pg
                )
                name = recv[0]
                # fix to https://stackoverflow.com/q/62748654/9191338
                # Python incorrectly tracks shared memory even if it is not
                # created by the process. The following patch is a workaround.
                with patch(
                    "multiprocessing.resource_tracker.register",
                    _ignore_resource_tracker_register,
                ):
                    shm = shared_memory.SharedMemory(name=name)
                if shm.buf[: len(magic_message)] == magic_message:
                    is_in_the_same_node[rank] = 1
    except Exception as exc:
        logger.error("Error ignored in is_in_the_same_node: %s", exc)
    finally:
        if shm:
            shm.close()

    torch.distributed.barrier(group=pg)

    # clean up the shared memory segment
    with contextlib.suppress(OSError):
        if rank == source_rank and shm:
            shm.unlink()
    torch.distributed.all_reduce(is_in_the_same_node, group=pg)

    return [x == 1 for x in is_in_the_same_node.tolist()]