diff --git a/invokeai/app/services/invoker.py b/invokeai/app/services/invoker.py
index e3fa6da8513..a7c9ae444d6 100644
--- a/invokeai/app/services/invoker.py
+++ b/invokeai/app/services/invoker.py
@@ -49,7 +49,7 @@ def create_execution_state(self, graph: Graph | None = None) -> GraphExecutionSt
         new_state = GraphExecutionState(graph=Graph() if graph is None else graph)
         self.services.graph_execution_manager.set(new_state)
         return new_state
-    
+
     def cancel(self, graph_execution_state_id: str) -> None:
         """Cancels the given execution state"""
         self.services.queue.cancel(graph_execution_state_id)
@@ -71,18 +71,12 @@ def _start(self) -> None:
         for service in vars(self.services):
             self.__start_service(getattr(self.services, service))
 
-        for service in vars(self.services):
-            self.__start_service(getattr(self.services, service))
-
     def stop(self) -> None:
         """Stops the invoker. A new invoker will have to be created to execute further."""
         # First stop all services
         for service in vars(self.services):
             self.__stop_service(getattr(self.services, service))
 
-        for service in vars(self.services):
-            self.__stop_service(getattr(self.services, service))
-
         self.services.queue.put(None)
 
 
diff --git a/invokeai/app/services/processor.py b/invokeai/app/services/processor.py
index c6229067503..35cbcd5068c 100644
--- a/invokeai/app/services/processor.py
+++ b/invokeai/app/services/processor.py
@@ -1,5 +1,5 @@
 import traceback
-from threading import Event, Thread
+from threading import Event, Thread, BoundedSemaphore
 
 from ..invocations.baseinvocation import InvocationContext
 from .invocation_queue import InvocationQueueItem
@@ -10,8 +10,11 @@ class DefaultInvocationProcessor(InvocationProcessorABC):
     __invoker_thread: Thread
     __stop_event: Event
     __invoker: Invoker
+    __threadLimit: BoundedSemaphore
 
     def start(self, invoker) -> None:
+        # if we do want multithreading at some point, we could make this configurable
+        self.__threadLimit = BoundedSemaphore(1)
         self.__invoker = invoker
         self.__stop_event = Event()
         self.__invoker_thread = Thread(
@@ -20,7 +23,7 @@ def start(self, invoker) -> None:
             kwargs=dict(stop_event=self.__stop_event),
         )
         self.__invoker_thread.daemon = (
-            True  # TODO: probably better to just not use threads?
+            True  # TODO: make async and do not use threads
         )
         self.__invoker_thread.start()
 
@@ -29,6 +32,7 @@ def stop(self, *args, **kwargs) -> None:
 
     def __process(self, stop_event: Event):
         try:
+            self.__threadLimit.acquire()
             while not stop_event.is_set():
                 queue_item: InvocationQueueItem = self.__invoker.services.queue.get()
                 if not queue_item:  # Probably stopping
@@ -110,7 +114,7 @@ def __process(self, stop_event: Event):
                     )
 
                     pass
-                
+
                 # Check queue to see if this is canceled, and skip if so
                 if self.__invoker.services.queue.is_canceled(
                     graph_execution_state.id
@@ -127,4 +131,6 @@ def __process(self, stop_event: Event):
                     )
 
         except KeyboardInterrupt:
-            ...  # Log something?
+            pass  # Log something? KeyboardInterrupt is probably not going to be seen by the processor
+        finally:
+            self.__threadLimit.release()