Initialize signal handlers after context (#1331)

Signed-off-by: Shane Loretz <[email protected]>

rclpy/rclpy/__init__.py

@@ -88,8 +88,12 @@ def __init__(self,
             self.installed_signal_handlers = False
         else:
             self.installed_signal_handlers = True
-        install_signal_handlers(signal_handler_options)
         self.context.init(args, domain_id=domain_id)
+        # Install signal handlers after initializing the context because the rclpy signal
+        # handler only does something if there is at least one initialized context.
+        # It is desirable for sigint or sigterm to be able to terminate the process if rcl_init
+        # takes a long time, and the default signal handlers work well for that purpose.
+        install_signal_handlers(signal_handler_options)
 
     def __enter__(self) -> 'InitContextManager':
         return self