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Artemis-Eapil/artemis/runtime/device_lock.py
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Python

# Copyright 2026 Google LLC
#
# 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.
"""Cross-process FIFO execution queue for the local Artemis device."""
from __future__ import annotations
from dataclasses import dataclass
from datetime import UTC, datetime
import json
import os
from pathlib import Path
import time
import uuid
from artemis.config.paths import get_temp_dir
class DeviceBusyError(RuntimeError):
"""Raised when another Artemis process already owns a device."""
@dataclass(frozen=True)
class DeviceLockOwner:
pid: int
process_created_at: float
token: str
device_id: str
description: str
acquired_at: str
session_id: str | None = None
ingress: str | None = None
@classmethod
def from_dict(cls, value: dict) -> DeviceLockOwner:
return cls(
pid=int(value["pid"]),
process_created_at=float(value["process_created_at"]),
token=str(value["token"]),
device_id=str(value["device_id"]),
description=str(value.get("description", "unknown task")),
acquired_at=str(value.get("acquired_at", "unknown time")),
session_id=(
str(value["session_id"])
if value.get("session_id") is not None
else None
),
ingress=(str(value["ingress"]) if value.get("ingress") is not None else None),
)
class DeviceExecutionLock:
"""A PID-aware FIFO lease shared by UI, CLI, SDK, and MCP tasks.
Artemis intentionally supports one active local device. A single global
queue therefore orders every local task regardless of which API or process
submitted it. Submission layers may reserve a queue ticket before spawning
a worker; the worker receives that token through the environment and claims
the same position. Tasks without a submission layer reserve at acquire time.
Atomic file creation provides exclusion. PID creation time prevents stale
owners or queue tickets from blocking execution after a process exits or
after the operating system reuses the same PID.
"""
_MALFORMED_LOCK_GRACE_SECONDS = 5.0
_DEFAULT_POLL_INTERVAL_SECONDS = 0.1
QUEUE_TICKET_ENV = "ARTEMIS_DEVICE_QUEUE_TICKET"
def __init__(
self,
device_id: str,
description: str = "Artemis task",
queue_ticket: str | None = None,
):
self.device_id = device_id
self.description = description
self.token = uuid.uuid4().hex
lock_dir = get_temp_dir("device-locks")
self.path = lock_dir / "artemis-global-device.lock"
self.queue_dir = lock_dir / "artemis-global-device.queue"
self.queue_ticket = queue_ticket or os.environ.pop(self.QUEUE_TICKET_ENV, None)
self.session_id = os.getenv("ARTEMIS_SESSION_ID") or os.getenv(
"ARTEMIS_CLOUD_SESSION_ID"
)
self.ingress = os.getenv("ARTEMIS_TASK_INGRESS") or "sdk"
self._queue_path: Path | None = None
self._acquired = False
@classmethod
def _global_lock_path(cls) -> Path:
return get_temp_dir("device-locks") / "artemis-global-device.lock"
@staticmethod
def _current_process_created_at() -> float:
try:
import psutil
return float(psutil.Process(os.getpid()).create_time())
except Exception:
return 0.0
@staticmethod
def _owner_is_alive(owner: DeviceLockOwner) -> bool:
try:
import psutil
process = psutil.Process(owner.pid)
if not process.is_running():
return False
if owner.process_created_at <= 0:
return True
return abs(process.create_time() - owner.process_created_at) < 1.0
except Exception:
return False
@staticmethod
def _read_owner(path: Path) -> DeviceLockOwner | None:
try:
payload = json.loads(path.read_text(encoding="utf-8"))
return DeviceLockOwner.from_dict(payload)
except (OSError, ValueError, KeyError, TypeError, json.JSONDecodeError):
return None
def _remove_stale_lock(self) -> bool:
owner = self._read_owner(self.path)
if owner is not None:
if self._owner_is_alive(owner):
return False
else:
try:
if time.time() - self.path.stat().st_mtime < self._MALFORMED_LOCK_GRACE_SECONDS:
return False
except OSError:
return True
try:
self.path.unlink(missing_ok=True)
return True
except OSError:
return False
@classmethod
def _owner_payload(
cls,
token: str,
device_id: str,
description: str,
*,
session_id: str | None = None,
ingress: str | None = None,
) -> dict:
payload = {
"pid": os.getpid(),
"process_created_at": cls._current_process_created_at(),
"token": token,
"device_id": device_id,
"description": description,
"acquired_at": datetime.now(UTC).isoformat(),
}
if session_id:
payload["session_id"] = str(session_id)
if ingress:
payload["ingress"] = str(ingress)
return payload
@classmethod
def reserve(
cls,
description: str = "Artemis task",
device_id: str = "pending",
*,
session_id: str | None = None,
ingress: str | None = None,
) -> str:
"""Reserve a global FIFO position before a worker process is spawned."""
token = uuid.uuid4().hex
queue_dir = get_temp_dir("device-locks") / "artemis-global-device.queue"
queue_dir.mkdir(parents=True, exist_ok=True)
payload = cls._owner_payload(
token,
device_id,
description,
session_id=session_id,
ingress=ingress,
)
for _ in range(8):
path = queue_dir / f"{time.time_ns():020d}-{token}.wait"
try:
fd = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY)
except FileExistsError:
continue
else:
try:
os.write(fd, json.dumps(payload, ensure_ascii=False).encode("utf-8"))
finally:
os.close(fd)
return token
raise DeviceBusyError("Could not reserve a position in the Artemis device queue.")
@classmethod
def cancel_reservation(cls, token: str | None) -> bool:
"""Remove a pending queue ticket. Active execution leases are untouched."""
if not token:
return False
queue_dir = get_temp_dir("device-locks") / "artemis-global-device.queue"
removed = False
for path in queue_dir.glob(f"*-{token}.wait"):
try:
path.unlink(missing_ok=True)
removed = True
except OSError:
pass
return removed
@classmethod
def transfer_reservation(
cls,
token: str,
pid: int,
*,
description: str = "Artemis task",
device_id: str = "pending",
session_id: str | None = None,
ingress: str | None = None,
) -> bool:
"""Transfer a submission ticket to its worker process.
This makes a ticket stale as soon as a worker that failed before Agent
initialization exits, instead of keeping it alive with the submitting
server process.
"""
queue_dir = get_temp_dir("device-locks") / "artemis-global-device.queue"
matches = list(queue_dir.glob(f"*-{token}.wait"))
path = min(matches, default=None)
if path is None:
return False
try:
import psutil
process_created_at = float(psutil.Process(pid).create_time())
except Exception:
process_created_at = 0.0
payload = {
"pid": pid,
"process_created_at": process_created_at,
"token": token,
"device_id": device_id,
"description": description,
"acquired_at": datetime.now(UTC).isoformat(),
}
if session_id:
payload["session_id"] = str(session_id)
if ingress:
payload["ingress"] = str(ingress)
try:
path.write_text(json.dumps(payload, ensure_ascii=False), encoding="utf-8")
except OSError:
return False
return True
def _find_reserved_ticket(self) -> Path | None:
if not self.queue_ticket:
return None
matches = list(self.queue_dir.glob(f"*-{self.queue_ticket}.wait"))
return min(matches, default=None)
def _claim_or_create_queue_ticket(self) -> Path:
self.queue_dir.mkdir(parents=True, exist_ok=True)
if self.queue_ticket:
path = self._find_reserved_ticket()
if path is None:
raise DeviceBusyError(
"The Artemis queue reservation was cancelled or expired before execution."
)
payload = self._owner_payload(
self.queue_ticket,
self.device_id,
self.description,
session_id=self.session_id,
ingress=self.ingress,
)
path.write_text(json.dumps(payload, ensure_ascii=False), encoding="utf-8")
return path
self.queue_ticket = self.reserve(self.description, self.device_id)
path = self._find_reserved_ticket()
if path is None:
raise DeviceBusyError("The Artemis device queue ticket could not be created.")
return path
def _remove_stale_queue_entries(self) -> int:
removed = 0
if not self.queue_dir.exists():
return removed
for path in self.queue_dir.glob("*.wait"):
if self._queue_path is not None and path == self._queue_path:
continue
owner = self._read_owner(path)
if owner is not None and self._owner_is_alive(owner):
continue
if owner is None:
try:
if time.time() - path.stat().st_mtime < self._MALFORMED_LOCK_GRACE_SECONDS:
continue
except OSError:
continue
try:
path.unlink(missing_ok=True)
removed += 1
except OSError:
pass
return removed
def _try_acquire_owner_lock(self) -> bool:
owner_payload = self._owner_payload(
self.token,
self.device_id,
self.description,
session_id=self.session_id,
ingress=self.ingress,
)
try:
fd = os.open(self.path, os.O_CREAT | os.O_EXCL | os.O_WRONLY)
except FileExistsError:
self._remove_stale_lock()
return False
try:
os.write(fd, json.dumps(owner_payload, ensure_ascii=False).encode("utf-8"))
finally:
os.close(fd)
self._acquired = True
return True
def acquire(
self,
*,
blocking: bool = True,
timeout: float | None = None,
poll_interval: float = _DEFAULT_POLL_INTERVAL_SECONDS,
cancel_event=None,
) -> None:
"""Wait in FIFO order and acquire exclusive access to the Artemis device."""
self._queue_path = self._claim_or_create_queue_ticket()
started_at = time.monotonic()
try:
while True:
if cancel_event is not None and cancel_event.is_set():
raise DeviceBusyError("Waiting for the Artemis device queue was cancelled.")
self._remove_stale_queue_entries()
queue = sorted(self.queue_dir.glob("*.wait"))
if not self._queue_path.exists():
raise DeviceBusyError("The Artemis queue reservation was cancelled.")
if queue and queue[0] == self._queue_path and self._try_acquire_owner_lock():
self._queue_path.unlink(missing_ok=True)
self._queue_path = None
return
if not blocking:
owner = self._read_owner(self.path)
owner_text = (
f"PID {owner.pid} ({owner.description}, since {owner.acquired_at})"
if owner is not None
else "an earlier queued task"
)
raise DeviceBusyError(
f"Device '{self.device_id}' is already controlled by {owner_text}."
)
if timeout is not None and time.monotonic() - started_at >= timeout:
raise DeviceBusyError(
f"Timed out waiting for the Artemis device queue after {timeout:.1f}s."
)
time.sleep(max(0.01, poll_interval))
except BaseException:
if self._queue_path is not None:
self._queue_path.unlink(missing_ok=True)
self._queue_path = None
raise
def release(self) -> None:
if not self._acquired:
return
try:
owner = self._read_owner(self.path)
if owner is not None and owner.token == self.token:
self.path.unlink(missing_ok=True)
finally:
self._acquired = False
@classmethod
def get_active_owner(cls) -> DeviceLockOwner | None:
"""Return the live process that currently owns the global device lease."""
path = cls._global_lock_path()
owner = None
for attempt in range(3):
owner = cls._read_owner(path)
if owner is not None or not path.exists():
break
if attempt < 2:
time.sleep(0.01)
if owner is None:
try:
if path.exists() and time.time() - path.stat().st_mtime >= cls._MALFORMED_LOCK_GRACE_SECONDS:
path.unlink(missing_ok=True)
except OSError:
pass
return None
if cls._owner_is_alive(owner):
return owner
try:
path.unlink(missing_ok=True)
except OSError:
pass
return None
@classmethod
def has_owner_record(cls) -> bool:
"""Return whether an owner record exists, including a record being written."""
return cls._global_lock_path().exists()
@classmethod
def is_active_owner(cls, expected: DeviceLockOwner) -> bool:
"""Revalidate a previously read owner before performing a destructive action."""
current = cls._read_owner(cls._global_lock_path())
return bool(
current
and current.token == expected.token
and current.pid == expected.pid
and abs(current.process_created_at - expected.process_created_at) < 1.0
and cls._owner_is_alive(current)
)
@classmethod
def annotate_active_owner(
cls,
*,
session_id: str,
ingress: str | None = None,
) -> bool:
"""Attach session metadata after tracing starts inside the lease owner."""
path = cls._global_lock_path()
owner = cls._read_owner(path)
if owner is None or owner.pid != os.getpid() or not cls._owner_is_alive(owner):
return False
payload = {
"pid": owner.pid,
"process_created_at": owner.process_created_at,
"token": owner.token,
"device_id": owner.device_id,
"description": owner.description,
"acquired_at": owner.acquired_at,
"session_id": str(session_id),
"ingress": ingress or owner.ingress or "sdk",
}
temp_path = path.with_name(f"{path.name}.{uuid.uuid4().hex}.tmp")
try:
temp_path.write_text(json.dumps(payload, ensure_ascii=False), encoding="utf-8")
os.replace(temp_path, path)
except OSError:
return False
finally:
try:
temp_path.unlink(missing_ok=True)
except OSError:
pass
return True
@classmethod
def cleanup_stale_locks(cls) -> int:
"""Remove execution leases and queue tickets whose owners are gone."""
removed = 0
lock_dir = get_temp_dir("device-locks")
for path in lock_dir.glob("*.lock"):
owner = cls._read_owner(path)
if owner is not None and cls._owner_is_alive(owner):
continue
if owner is None:
try:
if time.time() - path.stat().st_mtime < cls._MALFORMED_LOCK_GRACE_SECONDS:
continue
except OSError:
continue
try:
path.unlink(missing_ok=True)
removed += 1
except OSError:
pass
queue_dir = lock_dir / "artemis-global-device.queue"
for path in queue_dir.glob("*.wait"):
owner = cls._read_owner(path)
if owner is not None and cls._owner_is_alive(owner):
continue
if owner is None:
try:
if time.time() - path.stat().st_mtime < cls._MALFORMED_LOCK_GRACE_SECONDS:
continue
except OSError:
continue
try:
path.unlink(missing_ok=True)
removed += 1
except OSError:
pass
return removed