Add top-level try_shutdown method. (#1302)

I noticed that this was needed when trying to convert some
of the examples over to the context manager.  They currently
throw an exception because the signal handler does the
shutdown, and then leaving the context tries to do it
again.

This is also more symmetric with what shutdown() does,
in that it also uninstalls signal handlers.

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

rclpy/rclpy/__init__.py

@@ -56,7 +56,7 @@
 from rclpy.utilities import get_rmw_implementation_identifier  # noqa: F401
 from rclpy.utilities import ok  # noqa: F401 forwarding to this module
 from rclpy.utilities import shutdown as _shutdown
-from rclpy.utilities import try_shutdown  # noqa: F401
+from rclpy.utilities import try_shutdown as _try_shutdown
 
 # Avoid loading extensions on module import
 if TYPE_CHECKING:
@@ -100,7 +100,7 @@ def __exit__(
         exc_val: Optional[BaseException],
         exc_tb: Optional[TracebackType],
     ) -> None:
-        shutdown(context=self.context, uninstall_handlers=self.installed_signal_handlers)
+        try_shutdown(context=self.context, uninstall_handlers=self.installed_signal_handlers)
 
 
 def init(
@@ -171,6 +171,32 @@ def shutdown(
         uninstall_signal_handlers()
 
 
+def try_shutdown(
+    *,
+    context: Optional[Context] = None,
+    uninstall_handlers: Optional[bool] = None
+) -> None:
+    """
+    Shutdown a previously initialized context if not already shutdown.
+
+    This will also shutdown the global executor.
+
+    :param context: The context to invalidate. If ``None``, then the default context is used
+        (see :func:`.get_default_context`).
+    :param uninstall_handlers:
+        If `None`, signal handlers will be uninstalled when shutting down the default context.
+        If `True`, signal handlers will be uninstalled.
+        If `False`, signal handlers won't be uninstalled.
+    """
+    _try_shutdown(context=context)
+    if (
+        uninstall_handlers or (
+            uninstall_handlers is None and (
+                context is None or context is get_default_context()))
+    ):
+        uninstall_signal_handlers()
+
+
 def create_node(
     node_name: str,
     *,