Make service lients context-aware. (#1295)

This way it is much easier to create examples that properly
clean up after themselves.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

rclpy/rclpy/client.py

@@ -14,8 +14,10 @@
 
 import threading
 import time
+from types import TracebackType
 from typing import Dict
 from typing import Optional
+from typing import Type
 from typing import TypeVar
 
 from rclpy.callback_groups import CallbackGroup
@@ -224,3 +226,14 @@ def destroy(self):
            should call :meth:`.Node.destroy_client`.
         """
         self.__client.destroy_when_not_in_use()
+
+    def __enter__(self) -> 'Client':
+        return self
+
+    def __exit__(
+        self,
+        exc_type: Optional[Type[BaseException]],
+        exc_val: Optional[BaseException],
+        exc_tb: Optional[TracebackType],
+    ) -> None:
+        self.destroy()

rclpy/test/test_client.py

@@ -242,6 +242,22 @@ def _service(request, response):
             self.node.destroy_client(cli)
             self.node.destroy_service(srv)
 
+    def test_sync_call_context_manager(self):
+        def _service(request, response):
+            return response
+        with self.node.create_client(GetParameters, 'get/parameters') as cli:
+            with self.node.create_service(GetParameters, 'get/parameters', _service):
+                self.assertTrue(cli.wait_for_service(timeout_sec=20))
+                executor = rclpy.executors.SingleThreadedExecutor(context=self.context)
+                executor.add_node(self.node)
+                executor_thread = threading.Thread(
+                    target=TestClient._spin_rclpy_node, args=(self.node, executor))
+                executor_thread.start()
+                result = cli.call(GetParameters.Request(), 0.5)
+                self.assertTrue(result is not None)
+                executor.shutdown()
+                executor_thread.join()
+
 
 if __name__ == '__main__':
     unittest.main()