Make subscriptions context-manager aware. (#1291)

Signed-off-by: Chris Lalancette <[email protected]>

rclpy/rclpy/subscription.py

@@ -15,7 +15,8 @@
 
 from enum import Enum
 import inspect
-from typing import Callable, Generic, List, Type, TypeVar
+from types import TracebackType
+from typing import Callable, Generic, List, Optional, Type, TypeVar
 
 from rclpy.callback_groups import CallbackGroup
 from rclpy.event_handler import EventHandler, SubscriptionEventCallbacks
@@ -123,3 +124,14 @@ def callback(self, value: Callable[[MsgT], None]) -> None:
         raise RuntimeError(
             'Subscription.__init__(): callback should be either be callable with one argument'
             '(to get only the message) or two (to get message and message info)')
+
+    def __enter__(self) -> 'Subscription':
+        return self
+
+    def __exit__(
+        self,
+        exc_type: Optional[Type[BaseException]],
+        exc_val: Optional[BaseException],
+        exc_tb: Optional[TracebackType],
+    ) -> None:
+        self.destroy()