Check process lineage before join (lava-nc#177)

Signed-off-by: Marcus G K Williams <168222+mgkwill@users.noreply.github.com>

src/lava/magma/runtime/message_infrastructure/multiprocessing.py

@@ -8,6 +8,7 @@
         AbstractRuntimeServiceBuilder
 
 import multiprocessing as mp
+import os
 from multiprocessing.managers import SharedMemoryManager
 import traceback
 
@@ -76,7 +77,8 @@ def build_actor(self, target_fn: ty.Callable, builder: ty.Union[
     def stop(self):
         """Stops the shared memory manager"""
         for actor in self._actors:
-            actor.join()
+            if actor._parent_pid == os.getpid():
+                actor.join()
 
         self._smm.shutdown()