# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0

from __future__ import annotations

import asyncio
import itertools
import os
import signal
import socket
import subprocess
import sys
import textwrap
import threading
import time

import pynvml
import pytest
from gpu_memory_service.client import memory_manager as client_memory_manager
from gpu_memory_service.client.memory_manager import (
    GMSClientMemoryManager,
    StaleMemoryLayoutError,
)
from gpu_memory_service.client.rpc import _GMSRPCTransport
from gpu_memory_service.client.session import _GMSClientSession
from gpu_memory_service.common import cuda_utils
from gpu_memory_service.common.protocol.messages import (
    GetEventHistoryRequest,
    GetEventHistoryResponse,
    GetRuntimeStateRequest,
    GetRuntimeStateResponse,
)
from gpu_memory_service.common.types import (
    GrantedLockType,
    RequestedLockType,
    ServerState,
)
from gpu_memory_service.server import allocations as server_allocations
from gpu_memory_service.server.allocations import GMSAllocationManager
from gpu_memory_service.server.rpc import GMSRPCServer

from tests.gms.harness.gms import ServerThread

pytestmark = [
    pytest.mark.pre_merge,
    pytest.mark.unit,
    pytest.mark.gpu_0,
]


def _gpu_memory_free_bytes(device: int = 0) -> int:
    pynvml.nvmlInit()
    try:
        handle = pynvml.nvmlDeviceGetHandleByIndex(device)
        return int(pynvml.nvmlDeviceGetMemoryInfo(handle).free)
    finally:
        pynvml.nvmlShutdown()


def _drop_connection(session: _GMSClientSession) -> None:
    # Use a raw transport break here, not abort(), because these tests need to
    # simulate an unexpected socket loss while a request is still in flight.
    sock = session._transport._socket
    assert sock is not None
    try:
        sock.shutdown(socket.SHUT_RDWR)
    except OSError:
        pass
    sock.close()
    session._transport._socket = None


def _wait_for_server_state(
    server: GMSRPCServer,
    expected: ServerState,
    timeout: float = 2.0,
) -> None:
    deadline = time.monotonic() + timeout
    while server.state != expected:
        if time.monotonic() > deadline:
            raise TimeoutError(f"server did not reach {expected.name}")
        time.sleep(0.01)


def _wait_for_waiting_writers(
    server: GMSRPCServer,
    expected: int,
    timeout: float = 2.0,
) -> None:
    deadline = time.monotonic() + timeout
    while server._gms._sessions.snapshot().waiting_writers != expected:
        if time.monotonic() > deadline:
            raise TimeoutError(f"waiting writers did not reach {expected}")
        time.sleep(0.01)


def _wait_for_ro_session_count(
    server: GMSRPCServer,
    expected: int,
    timeout: float = 2.0,
) -> None:
    deadline = time.monotonic() + timeout
    while server._gms._sessions.snapshot().ro_session_count != expected:
        if time.monotonic() > deadline:
            raise TimeoutError(f"RO session count did not reach {expected}")
        time.sleep(0.01)


@pytest.fixture
def real_gms(monkeypatch, tmp_path):
    server_handles = itertools.count(1000)
    client_handles = itertools.count(10000)
    next_va = itertools.count(0x100000, 0x10000)

    monkeypatch.setattr(server_allocations, "cuda_ensure_initialized", lambda: None)
    monkeypatch.setattr(
        server_allocations,
        "cumem_get_allocation_granularity",
        lambda device: 4096,
    )
    monkeypatch.setattr(
        server_allocations,
        "cumem_create_tolerate_oom",
        lambda size, device: (True, next(server_handles)),
    )
    monkeypatch.setattr(server_allocations, "cumem_release", lambda handle: None)

    def export_fd(handle: int) -> int:
        read_fd, write_fd = os.pipe()
        os.close(write_fd)
        return read_fd

    monkeypatch.setattr(
        server_allocations, "cumem_export_to_shareable_handle", export_fd
    )

    monkeypatch.setattr(
        client_memory_manager, "cuda_set_current_device", lambda device: None
    )
    monkeypatch.setattr(
        client_memory_manager,
        "cumem_get_allocation_granularity",
        lambda device: 4096,
    )
    monkeypatch.setattr(client_memory_manager, "cuda_synchronize", lambda: None)
    monkeypatch.setattr(
        client_memory_manager,
        "cumem_address_reserve",
        lambda size, granularity: next(next_va),
    )
    monkeypatch.setattr(
        client_memory_manager,
        "cumem_address_free",
        lambda va, size: None,
    )
    monkeypatch.setattr(
        client_memory_manager, "cumem_map", lambda va, size, handle: None
    )
    monkeypatch.setattr(
        client_memory_manager,
        "cumem_set_access",
        lambda va, size, device, mode: None,
    )
    monkeypatch.setattr(client_memory_manager, "cumem_unmap", lambda va, size: None)
    monkeypatch.setattr(client_memory_manager, "cumem_release", lambda handle: None)
    monkeypatch.setattr(client_memory_manager, "cuda_validate_pointer", lambda va: True)

    def import_fd(fd: int) -> int:
        os.close(fd)
        return next(client_handles)

    monkeypatch.setattr(
        client_memory_manager,
        "cumem_import_from_shareable_handle_close_fd",
        import_fd,
    )

    socket_path = str(tmp_path / "gms.sock")
    server = GMSRPCServer(socket_path, device=0, allocation_retry_interval=0.01)
    thread = ServerThread(server, socket_path)
    thread.start()
    try:
        yield server, socket_path
    finally:
        thread.stop()


def test_rw_commit_publishes_allocations_metadata_and_layout_hash(real_gms):
    server, socket_path = real_gms

    writer = GMSClientMemoryManager(socket_path, device=0)
    writer.connect(RequestedLockType.RW)
    va = writer.create_mapping(size=4096, tag="weights")
    allocation_id = writer.mappings[va].allocation_id
    writer.metadata_put("tensor.0", allocation_id, 0, b"weights")
    assert writer.commit()

    reader = _GMSClientSession(socket_path, RequestedLockType.RO, None)
    try:
        assert reader.lock_type == GrantedLockType.RO
        assert reader.committed
        assert len(reader.list_allocations()) == 1
        assert reader.metadata_get("tensor.0") == (allocation_id, 0, b"weights")
        assert reader.get_memory_layout_hash()
    finally:
        reader.close()

    assert writer.is_unmapped
    assert not writer.is_connected
    _wait_for_server_state(server, ServerState.COMMITTED)


def test_rw_disconnect_aborts_layout_and_next_writer_starts_clean(real_gms):
    server, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    allocation_id, _ = writer.allocate(4096, "weights")
    writer.metadata_put("stale", allocation_id, 0, b"value")
    _drop_connection(writer)

    _wait_for_server_state(server, ServerState.EMPTY)

    next_writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    try:
        assert next_writer.list_allocations() == []
        assert next_writer.metadata_list() == []
    finally:
        next_writer.close()


def test_rw_or_ro_grants_rw_from_empty_and_ro_from_committed(real_gms):
    server, socket_path = real_gms

    session = _GMSClientSession(socket_path, RequestedLockType.RW_OR_RO, 100)
    assert session.lock_type == GrantedLockType.RW
    session.commit()

    _wait_for_server_state(server, ServerState.COMMITTED)

    session = _GMSClientSession(socket_path, RequestedLockType.RW_OR_RO, 100)
    try:
        assert session.lock_type == GrantedLockType.RO
        assert session.committed
    finally:
        session.close()


def test_runtime_state_and_event_history_are_side_effect_free(real_gms):
    server, socket_path = real_gms

    writer = GMSClientMemoryManager(socket_path, device=0)
    writer.connect(RequestedLockType.RW)
    writer.create_mapping(size=4096, tag="weights")
    assert writer.commit()

    assert server._gms._sessions.snapshot().ro_session_count == 0

    with _GMSRPCTransport(socket_path) as transport:
        transport.connect()
        state = transport.request(
            GetRuntimeStateRequest(),
            GetRuntimeStateResponse,
        )

    with _GMSRPCTransport(socket_path) as transport:
        transport.connect()
        history = transport.request(
            GetEventHistoryRequest(),
            GetEventHistoryResponse,
        )

    assert state.state == ServerState.COMMITTED.name
    assert state.committed
    assert state.is_ready
    assert state.ro_session_count == 0
    assert state.waiting_writers == 0
    assert state.allocation_count == 1
    assert state.memory_layout_hash
    assert [event.kind for event in history.events] == ["rw_connected", "committed"]
    assert server._gms._sessions.snapshot().ro_session_count == 0


def test_committed_layout_is_replaced_when_new_writer_connects(real_gms):
    server, socket_path = real_gms

    first_writer = GMSClientMemoryManager(socket_path, device=0)
    first_writer.connect(RequestedLockType.RW)
    first_writer.create_mapping(size=4096, tag="weights")
    assert first_writer.commit()

    _wait_for_server_state(server, ServerState.COMMITTED)
    assert server._gms.allocation_count == 1

    second_writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    try:
        assert second_writer.lock_type == GrantedLockType.RW
        assert second_writer.list_allocations() == []
        assert second_writer.metadata_list() == []
        assert server._gms.allocation_count == 0
        assert server.state == ServerState.RW
        assert not server._gms.committed
    finally:
        second_writer.close()


def test_reader_mapping_disconnect_then_next_writer_clears_old_layout(real_gms):
    server, socket_path = real_gms

    writer = GMSClientMemoryManager(socket_path, device=0)
    writer.connect(RequestedLockType.RW)
    va = writer.create_mapping(size=4096, tag="weights")
    allocation_id = writer.mappings[va].allocation_id
    assert writer.commit()

    reader = GMSClientMemoryManager(socket_path, device=0)
    reader.connect(RequestedLockType.RO)
    imported_va = reader.create_mapping(allocation_id=allocation_id)
    assert reader.mappings[imported_va].handle != 0

    next_writer_result: dict[str, object] = {}

    def open_writer() -> None:
        try:
            next_writer_result["session"] = _GMSClientSession(
                socket_path,
                RequestedLockType.RW,
                500,
            )
        except Exception as exc:
            next_writer_result["error"] = exc

    thread = threading.Thread(target=open_writer)
    thread.start()
    _wait_for_waiting_writers(server, 1)

    assert thread.is_alive()
    assert server.state == ServerState.RO
    assert server._gms.allocation_count == 1

    reader.unmap_all_vas()
    reader.abort()
    thread.join(timeout=2)

    next_writer = next_writer_result.get("session")
    assert isinstance(next_writer, _GMSClientSession)
    try:
        assert next_writer.lock_type == GrantedLockType.RW
        assert next_writer.list_allocations() == []
        assert server._gms.allocation_count == 0
        assert server.state == ServerState.RW
        assert not server._gms.committed
    finally:
        next_writer.close()


def test_waiting_writer_blocks_new_readers_until_last_reader_disconnects(real_gms):
    server, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    writer.commit()

    reader = _GMSClientSession(socket_path, RequestedLockType.RO, None)
    writer_result: dict[str, object] = {}

    def open_writer() -> None:
        try:
            writer_result["session"] = _GMSClientSession(
                socket_path,
                RequestedLockType.RW,
                500,
            )
        except Exception as exc:
            writer_result["error"] = exc

    thread = threading.Thread(target=open_writer)
    thread.start()
    _wait_for_waiting_writers(server, 1)

    with pytest.raises(TimeoutError, match="Timeout waiting for lock"):
        _GMSClientSession(socket_path, RequestedLockType.RO, 100)

    reader.close()
    thread.join(timeout=2)

    waiting_writer = writer_result.get("session")
    assert isinstance(waiting_writer, _GMSClientSession)
    try:
        assert waiting_writer.lock_type == GrantedLockType.RW
    finally:
        waiting_writer.close()


def test_rw_or_ro_times_out_while_writer_waits_behind_reader(real_gms):
    server, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    writer.commit()

    reader = _GMSClientSession(socket_path, RequestedLockType.RO, None)
    waiting_writer: dict[str, object] = {}

    def block_writer() -> None:
        try:
            waiting_writer["session"] = _GMSClientSession(
                socket_path,
                RequestedLockType.RW,
                500,
            )
        except Exception as exc:
            waiting_writer["error"] = exc

    thread = threading.Thread(target=block_writer)
    thread.start()
    _wait_for_waiting_writers(server, 1)

    with pytest.raises(TimeoutError, match="Timeout waiting for lock"):
        _GMSClientSession(socket_path, RequestedLockType.RW_OR_RO, 100)

    reader.close()
    thread.join(timeout=2)
    granted_writer = waiting_writer.get("session")
    assert isinstance(granted_writer, _GMSClientSession)
    granted_writer.close()


def test_reader_can_acquire_after_waiting_writer_times_out(real_gms):
    server, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    writer.commit()

    reader = _GMSClientSession(socket_path, RequestedLockType.RO, None)
    writer_result: dict[str, BaseException | None] = {"error": None}

    def timeout_writer() -> None:
        try:
            _GMSClientSession(socket_path, RequestedLockType.RW, 100)
        except BaseException as exc:
            writer_result["error"] = exc

    thread = threading.Thread(target=timeout_writer)
    thread.start()
    _wait_for_waiting_writers(server, 1)
    thread.join(timeout=2)

    assert isinstance(writer_result["error"], TimeoutError)
    _wait_for_waiting_writers(server, 0)

    second_reader = _GMSClientSession(socket_path, RequestedLockType.RO, 200)
    try:
        assert second_reader.lock_type == GrantedLockType.RO
    finally:
        second_reader.close()
        reader.close()


def test_multiple_readers_hold_committed_state_until_last_disconnect(real_gms):
    server, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    writer.commit()

    reader_a = _GMSClientSession(socket_path, RequestedLockType.RO, None)
    reader_b = _GMSClientSession(socket_path, RequestedLockType.RO, None)

    _wait_for_server_state(server, ServerState.RO)
    assert server._gms._sessions.snapshot().ro_session_count == 2

    reader_a.close()
    _wait_for_ro_session_count(server, 1)
    assert server.state == ServerState.RO

    reader_b.close()
    _wait_for_server_state(server, ServerState.COMMITTED)


def test_ro_session_rejects_rw_only_requests(real_gms):
    _, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    writer.commit()

    reader = _GMSClientSession(socket_path, RequestedLockType.RO, None)
    try:
        with pytest.raises(RuntimeError, match="not allowed for RO session"):
            reader.allocate(4096, "weights")
        with pytest.raises(RuntimeError, match="not allowed for RO session"):
            reader.commit()
    finally:
        reader.close()


def test_lock_and_allocation_state_requests_reflect_real_server_state(real_gms):
    _, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    allocation_id, _ = writer.allocate(4096, "weights")

    lock_state = writer.get_lock_state()
    allocation_state = writer.get_allocation_state()

    assert lock_state.state == ServerState.RW.name
    assert lock_state.has_rw_session
    assert lock_state.ro_session_count == 0
    assert allocation_state.allocation_count == 1

    writer.metadata_put("tensor.0", allocation_id, 0, b"x")
    writer.commit()

    reader = _GMSClientSession(socket_path, RequestedLockType.RO, None)
    try:
        lock_state = reader.get_lock_state()
        allocation_state = reader.get_allocation_state()
        assert lock_state.state == ServerState.RO.name
        assert not lock_state.has_rw_session
        assert lock_state.ro_session_count == 1
        assert allocation_state.allocation_count == 1
    finally:
        reader.close()


def test_invalid_metadata_offset_is_rejected_without_mutating_state(real_gms):
    _, socket_path = real_gms

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    try:
        allocation_id, _ = writer.allocate(4096, "weights")
        with pytest.raises(RuntimeError, match="out of range"):
            writer.metadata_put("tensor.bad", allocation_id, 4096, b"x")
        assert writer.metadata_list() == []
    finally:
        writer.close()


def test_destroy_mapping_frees_allocation_and_metadata(real_gms):
    _, socket_path = real_gms

    writer = GMSClientMemoryManager(socket_path, device=0)
    writer.connect(RequestedLockType.RW)
    va = writer.create_mapping(size=4096, tag="weights")
    allocation_id = writer.mappings[va].allocation_id
    writer.metadata_put("tensor.0", allocation_id, 0, b"payload")

    writer.destroy_mapping(va)

    assert writer.list_handles() == []
    assert writer.metadata_list() == []
    writer.abort()


def test_remap_all_vas_succeeds_when_committed_layout_is_unchanged(real_gms):
    _, socket_path = real_gms

    writer = GMSClientMemoryManager(socket_path, device=0)
    writer.connect(RequestedLockType.RW)
    va = writer.create_mapping(size=4096, tag="weights")
    allocation_id = writer.mappings[va].allocation_id
    assert writer.commit()

    reader = GMSClientMemoryManager(socket_path, device=0)
    reader.connect(RequestedLockType.RO)
    imported_va = reader.create_mapping(allocation_id=allocation_id)
    imported_mapping = reader.mappings[imported_va]
    reader.unmap_all_vas()
    reader.abort()

    reader.connect(RequestedLockType.RO)
    reader.remap_all_vas()

    assert reader.mappings[imported_va].handle != 0
    assert reader.mappings[imported_va].allocation_id == imported_mapping.allocation_id
    reader.close()


def test_remap_all_vas_rejects_stale_layout_after_new_layout_commit(real_gms):
    _, socket_path = real_gms

    writer = GMSClientMemoryManager(socket_path, device=0)
    writer.connect(RequestedLockType.RW)
    va = writer.create_mapping(size=4096, tag="weights")
    allocation_id = writer.mappings[va].allocation_id
    assert writer.commit()

    reader = GMSClientMemoryManager(socket_path, device=0)
    reader.connect(RequestedLockType.RO)
    reader.create_mapping(allocation_id=allocation_id)
    reader.unmap_all_vas()
    reader.abort()

    next_writer = GMSClientMemoryManager(socket_path, device=0)
    next_writer.connect(RequestedLockType.RW)
    next_writer.create_mapping(size=8192, tag="weights")
    assert next_writer.commit()

    reader.connect(RequestedLockType.RO)
    with pytest.raises(StaleMemoryLayoutError, match="Layout changed"):
        reader.remap_all_vas()
    reader.abort()


def test_remap_all_vas_accepts_new_layout_with_same_structural_layout(real_gms):
    _, socket_path = real_gms

    first_writer = GMSClientMemoryManager(socket_path, device=0)
    first_writer.connect(RequestedLockType.RW)
    va = first_writer.create_mapping(size=4096, tag="weights")
    first_allocation_id = first_writer.mappings[va].allocation_id
    first_writer.metadata_put("tensor.0", first_allocation_id, 0, b"shape")
    assert first_writer.commit()

    reader = GMSClientMemoryManager(socket_path, device=0)
    reader.connect(RequestedLockType.RO)
    imported_va = reader.create_mapping(allocation_id=first_allocation_id)
    reader.unmap_all_vas()
    reader.abort()

    second_writer = GMSClientMemoryManager(socket_path, device=0)
    second_writer.connect(RequestedLockType.RW)
    second_va = second_writer.create_mapping(size=4096, tag="weights")
    second_allocation_id = second_writer.mappings[second_va].allocation_id
    assert second_allocation_id != first_allocation_id
    second_writer.metadata_put("tensor.0", second_allocation_id, 0, b"shape")
    assert second_writer.commit()

    reader.connect(RequestedLockType.RO)
    reader.remap_all_vas()

    assert reader.mappings[imported_va].va == imported_va
    assert reader.mappings[imported_va].allocation_id == second_allocation_id
    assert reader.metadata_get("tensor.0") == (second_allocation_id, 0, b"shape")
    reader.close()


def test_reallocate_all_handles_reuses_preserved_vas_in_new_layout(real_gms):
    server, socket_path = real_gms

    manager = GMSClientMemoryManager(socket_path, device=0)
    manager.connect(RequestedLockType.RW)
    va = manager.create_mapping(size=4096, tag="weights")
    old_allocation_id = manager.mappings[va].allocation_id
    assert manager.commit()

    _wait_for_server_state(server, ServerState.COMMITTED)
    manager.connect(RequestedLockType.RW)
    manager.reallocate_all_handles(tag="weights")

    assert manager.mappings[va].allocation_id != old_allocation_id
    assert manager.mappings[va].handle == 0

    manager.remap_all_vas()

    assert manager.mappings[va].va == va
    assert manager.mappings[va].handle != 0
    manager.close()
    _wait_for_server_state(server, ServerState.EMPTY)


def test_same_process_republish_remaps_against_new_committed_hash(real_gms):
    _, socket_path = real_gms

    manager = GMSClientMemoryManager(socket_path, device=0)
    manager.connect(RequestedLockType.RW)
    va = manager.create_mapping(size=4096, tag="weights")
    first_allocation_id = manager.mappings[va].allocation_id
    manager.metadata_put("tensor", first_allocation_id, 0, b"publish-1")
    assert manager.commit()

    manager.connect(RequestedLockType.RO)
    manager.remap_all_vas()
    manager.unmap_all_vas()
    manager.abort()

    manager.connect(RequestedLockType.RW)
    manager.reallocate_all_handles(tag="weights")
    second_allocation_id = manager.mappings[va].allocation_id
    assert second_allocation_id != first_allocation_id
    manager.remap_all_vas()
    manager.metadata_put("tensor", second_allocation_id, 0, b"publish-2")
    assert manager.commit()

    manager.connect(RequestedLockType.RO)
    manager.remap_all_vas()

    assert manager.mappings[va].va == va
    assert manager.mappings[va].allocation_id == second_allocation_id
    assert manager.metadata_get("tensor") == (second_allocation_id, 0, b"publish-2")

    manager.close()


def test_disconnect_during_allocation_retry_aborts_writer_and_unblocks_next_writer(
    real_gms,
    monkeypatch,
):
    server, socket_path = real_gms
    oom_attempts = 0
    allow_allocation = False

    def always_oom(size: int, device: int) -> tuple[bool, int]:
        nonlocal oom_attempts
        nonlocal allow_allocation
        if allow_allocation:
            return True, 4242
        oom_attempts += 1
        return False, 0

    monkeypatch.setattr(
        "gpu_memory_service.server.allocations.cumem_create_tolerate_oom",
        always_oom,
    )

    writer = _GMSClientSession(socket_path, RequestedLockType.RW, None)
    result: dict[str, BaseException] = {}

    def allocate() -> None:
        try:
            writer.allocate(4096, "weights")
        except BaseException as exc:
            result["error"] = exc

    thread = threading.Thread(target=allocate)
    thread.start()
    deadline = time.monotonic() + 2.0
    while oom_attempts == 0:
        if time.monotonic() > deadline:
            raise TimeoutError("allocation retry never reached CUDA OOM")
        time.sleep(0.01)

    _drop_connection(writer)

    thread.join(timeout=2)
    _wait_for_server_state(server, ServerState.EMPTY)

    allow_allocation = True
    next_writer = _GMSClientSession(socket_path, RequestedLockType.RW, 200)
    try:
        assert next_writer.lock_type == GrantedLockType.RW
        allocation_id, aligned_size = next_writer.allocate(4096, "weights")
        assert allocation_id
        assert aligned_size == 4096
    finally:
        next_writer.close()

    assert isinstance(result.get("error"), ConnectionError)


@pytest.mark.asyncio
@pytest.mark.timeout(180)
async def test_new_layout_large_allocation_waits_for_dead_writer_process(
    tmp_path,
    monkeypatch,
):
    free_before = _gpu_memory_free_bytes()
    size = int(free_before * 0.9)
    assert size > 0

    oom_failures = 0

    def count_oom(size: int, device: int) -> tuple[bool, int]:
        nonlocal oom_failures
        allocated, handle = cuda_utils.cumem_create_tolerate_oom(size, device)
        if not allocated:
            oom_failures += 1
        return allocated, handle

    monkeypatch.setattr(
        "gpu_memory_service.server.allocations.cumem_create_tolerate_oom",
        count_oom,
    )

    allocations = GMSAllocationManager(
        device=0,
        allocation_retry_interval=0.1,
        allocation_retry_timeout=120.0,
    )
    holder = None
    allocation_task = None

    try:
        first = await allocations.allocate(
            size=size,
            tag="weights",
            is_connected=lambda: True,
        )
        assert first.layout_slot == 0

        free_after_first = _gpu_memory_free_bytes()
        assert free_after_first < free_before - (size // 2)

        exported_fd = allocations.export_allocation(first.allocation_id)
        holder_ready = tmp_path / "holder.ready"
        holder_log = tmp_path / "holder.log"
        holder_script = tmp_path / "hold_import.py"
        holder_script.write_text(
            textwrap.dedent(
                """
                import sys
                import time
                from pathlib import Path

                fd = int(sys.argv[1])
                Path(sys.argv[2]).write_text(str(fd))

                while True:
                    time.sleep(1.0)
                """
            ),
            encoding="utf-8",
        )

        with holder_log.open("w", encoding="utf-8") as log_file:
            holder = subprocess.Popen(
                [
                    sys.executable,
                    str(holder_script),
                    str(exported_fd),
                    str(holder_ready),
                ],
                pass_fds=[exported_fd],
                stdout=log_file,
                stderr=subprocess.STDOUT,
                start_new_session=True,
            )
        os.close(exported_fd)

        deadline = time.monotonic() + 30.0
        while not holder_ready.exists():
            assert holder.poll() is None, holder_log.read_text(encoding="utf-8")
            assert time.monotonic() < deadline, holder_log.read_text(encoding="utf-8")
            await asyncio.sleep(0.1)

        allocations.clear_all()
        assert allocations.allocation_count == 0

        allocation_task = asyncio.create_task(
            allocations.allocate(
                size=size,
                tag="weights",
                is_connected=lambda: True,
            )
        )

        deadline = time.monotonic() + 30.0
        while oom_failures == 0:
            assert holder.poll() is None, holder_log.read_text(encoding="utf-8")
            assert not allocation_task.done()
            assert time.monotonic() < deadline
            await asyncio.sleep(0.1)

        assert oom_failures > 0
        assert not allocation_task.done()

        os.killpg(os.getpgid(holder.pid), signal.SIGKILL)
        holder.wait(timeout=30.0)

        second = await asyncio.wait_for(allocation_task, timeout=120.0)
        assert second.layout_slot == 0
        assert allocations.allocation_count == 1

        allocations.clear_all()
        assert allocations.allocation_count == 0

        deadline = time.monotonic() + 30.0
        while _gpu_memory_free_bytes() < free_before - (1 << 30):
            assert time.monotonic() < deadline
            await asyncio.sleep(0.1)
    finally:
        if allocation_task is not None and not allocation_task.done():
            allocation_task.cancel()
            try:
                await allocation_task
            except asyncio.CancelledError:
                pass
        if allocations.allocation_count > 0:
            allocations.clear_all()
        if holder is not None and holder.poll() is None:
            os.killpg(os.getpgid(holder.pid), signal.SIGKILL)
            holder.wait(timeout=30.0)
