Added support for multiple clients to be ran at the same time.

ptlinux/locking.py

@@ -7,13 +7,51 @@ from datetime import datetime
 import fcntl
 import os
 from pathlib import Path
-from typing import Iterator
+from typing import Iterator, TextIO
 
 
 class OperationBusyError(RuntimeError):
 	"""Raised when another launcher-prefix operation is still active."""
 
 
+class LauncherPlayLease:
+	"""Exclusive preparation lease that can become a shared game lease."""
+
+	def __init__(
+		self,
+		handle: TextIO | None,
+		*,
+		preparation_allowed: bool,
+		record_owned: bool,
+	) -> None:
+		self._handle = handle
+		self.preparation_allowed = preparation_allowed
+		self._record_owned = record_owned
+		self._shared = not preparation_allowed
+
+	@classmethod
+	def dry_run(cls) -> LauncherPlayLease:
+		return cls(None, preparation_allowed=True, record_owned=False)
+
+	@property
+	def shared(self) -> bool:
+		return self._shared
+
+	def allow_shared_clients(self) -> None:
+		"""Downgrade after all runtime mutations have completed."""
+
+		if self._shared:
+			return
+		if self._handle is not None:
+			_write_owner(self._handle, "play")
+			fcntl.flock(self._handle.fileno(), fcntl.LOCK_SH)
+		self._shared = True
+
+	@property
+	def record_owned(self) -> bool:
+		return self._record_owned
+
+
 @contextmanager
 def launcher_operation_lock(lock_path: Path, operation: str) -> Iterator[None]:
 	lock_path.parent.mkdir(parents=True, exist_ok=True)
@@ -26,13 +64,7 @@ def launcher_operation_lock(lock_path: Path, operation: str) -> Iterator[None]:
 			raise OperationBusyError(
 				f"launcher files are busy ({owner}); wait for it to finish 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()
+		_write_owner(handle, operation)
 		try:
 			yield
 		finally:
@@ -40,3 +72,67 @@ def launcher_operation_lock(lock_path: Path, operation: str) -> Iterator[None]:
 			handle.truncate()
 			handle.flush()
 			fcntl.flock(handle.fileno(), fcntl.LOCK_UN)
+
+
+@contextmanager
+def launcher_play_lock(
+	lock_path: Path,
+	operation: str = "play",
+) -> Iterator[LauncherPlayLease]:
+	"""Serialize preparation, then allow multiple active game clients.
+
+	The first play process acquires an exclusive lease so it may safely rebuild
+	the runtime view or prefix. It downgrades that lease immediately before
+	starting Game.exe. Later play processes then receive shared, read-only leases,
+	while updates and repairs remain excluded until every client exits.
+	"""
+
+	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:
+			try:
+				fcntl.flock(handle.fileno(), fcntl.LOCK_SH | fcntl.LOCK_NB)
+			except BlockingIOError as exc:
+				owner = _read_owner(handle)
+				raise OperationBusyError(
+					f"launcher files are busy ({owner}); wait for it to finish and try again"
+				) from exc
+			lease = LauncherPlayLease(
+				handle,
+				preparation_allowed=False,
+				record_owned=False,
+			)
+		else:
+			_write_owner(handle, f"{operation} preparation")
+			lease = LauncherPlayLease(
+				handle,
+				preparation_allowed=True,
+				record_owned=True,
+			)
+		try:
+			yield lease
+		finally:
+			# A downgraded owner record remains useful while any secondary shared
+			# lease is active. The next exclusive operation atomically replaces it.
+			if lease.record_owned and not lease.shared:
+				handle.seek(0)
+				handle.truncate()
+				handle.flush()
+			fcntl.flock(handle.fileno(), fcntl.LOCK_UN)
+
+
+def _read_owner(handle: TextIO) -> str:
+	handle.seek(0)
+	return handle.read().strip() or "unknown operation"
+
+
+def _write_owner(handle: TextIO, operation: str) -> None:
+	handle.seek(0)
+	handle.truncate()
+	handle.write(
+		f"{operation}, pid={os.getpid()}, "
+		f"started={datetime.now().astimezone().isoformat()}\n"
+	)
+	handle.flush()