Add simple lock thing

Author: tulir

mautrix/util/__init__.py

@@ -1,2 +1,2 @@
 __all__ = ["formatter", "color_log", "config", "signed_token", "simple_template", "manhole",
-           "markdown"]
+           "markdown", "simple_lock"]

mautrix/util/simple_lock.py

@@ -0,0 +1,41 @@
+# Copyright (c) 2020 Tulir Asokan
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+from typing import Optional
+import logging
+import asyncio
+
+
+class SimpleLock:
+    _loop: asyncio.AbstractEventLoop
+    _future: Optional[asyncio.Future]
+    log: Optional[logging.Logger]
+    message: Optional[str]
+
+    def __init__(self, message: Optional[str] = None, log: Optional[logging.Logger] = None,
+                 loop: Optional[asyncio.AbstractEventLoop] = None) -> None:
+        self._future = None
+        self._loop = loop or asyncio.get_event_loop()
+        self.log = log
+        self.message = message
+
+    def __enter__(self) -> None:
+        if self._future is None or self._future.done():
+            self._future = self._loop.create_future()
+
+    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
+        if self._future is not None:
+            self._future.set_result(None)
+            self._future = None
+
+    @property
+    def locked(self) -> bool:
+        return self._future is not None and not self._future.done()
+
+    async def wait(self, task: Optional[str] = None) -> None:
+        if self._future is not None:
+            if self.log and self.message:
+                self.log.debug(self.message, task)
+            await self._future