Init

ptlinux/locking.py

@@ -0,0 +1,42 @@
+"""Cross-process locks for launcher-prefix mutations."""
+
+from __future__ import annotations
+
+from contextlib import contextmanager
+from datetime import datetime
+import fcntl
+import os
+from pathlib import Path
+from typing import Iterator
+
+
+class OperationBusyError(RuntimeError):
+	"""Raised when another launcher-prefix operation is still active."""
+
+
+@contextmanager
+def launcher_operation_lock(lock_path: Path, operation: str) -> Iterator[None]:
+	lock_path.parent.mkdir(parents=True, exist_ok=True)
+	with lock_path.open("a+", encoding="utf-8") as handle:
+		try:
+			fcntl.flock(handle.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
+		except BlockingIOError as exc:
+			handle.seek(0)
+			owner = handle.read().strip() or "unknown operation"
+			raise OperationBusyError(
+				f"launcher files are busy ({owner}); close the updater and try again"
+			) from exc
+		handle.seek(0)
+		handle.truncate()
+		handle.write(
+			f"{operation}, pid={os.getpid()}, "
+			f"started={datetime.now().astimezone().isoformat()}\n"
+		)
+		handle.flush()
+		try:
+			yield
+		finally:
+			handle.seek(0)
+			handle.truncate()
+			handle.flush()
+			fcntl.flock(handle.fileno(), fcntl.LOCK_UN)