Release loop lock before waiting for it to do work (#369)

Main thread can be blocked trying to acquire
__loop_from_run_thread_lock while emit_event() in another thread is
holding that lock and waiting for the main thread to emit the event.
This change releases the lock before blocking.

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

Author: sloretz

launch/launch/launch_service.py

@@ -127,18 +127,22 @@ def emit_event(self, event: Event) -> None:
 
         If the LaunchService is not running, the event is queued until it is.
         """
+        future = None
         with self.__loop_from_run_thread_lock:
             if self.__loop_from_run_thread is not None:
                 # loop is in use, asynchronously emit the event
                 future = asyncio.run_coroutine_threadsafe(
                     self.__context.emit_event(event),
                     self.__loop_from_run_thread
                 )
-                future.result()
             else:
                 # loop is not in use, synchronously emit the event, and it will be processed later
                 self.__context.emit_event_sync(event)
 
+        if future is not None:
+            # Block until asynchronously emitted event is emitted by loop
+            future.result()
+
     def include_launch_description(self, launch_description: LaunchDescription) -> None:
         """
         Evaluate a given LaunchDescription and visits all of its entities.