Fix some potential issues related to threads.

main.py

@@ -371,6 +371,18 @@ class PromptQueue:
                     return True
         return False
 
+    def get_history(self):
+        with self.mutex:
+            return copy.deepcopy(self.history)
+
+    def wipe_history(self):
+        with self.mutex:
+            self.history = {}
+
+    def delete_history_item(self, id_to_delete):
+        with self.mutex:
+            self.history.pop(id_to_delete, None)
+
 async def run(server, address='', port=8188):
     await asyncio.gather(server.start(address, port), server.publish_loop())
 

server.py

@@ -82,7 +82,7 @@ class PromptServer():
 
         @routes.get("/history")
         async def get_history(request):
-            return web.json_response(self.prompt_queue.history)
+            return web.json_response(self.prompt_queue.get_history())
 
         @routes.get("/queue")
         async def get_queue(request):
@@ -146,11 +146,11 @@ class PromptServer():
             json_data =  await request.json()
             if "clear" in json_data:
                 if json_data["clear"]:
-                    self.prompt_queue.history = {}
+                    self.prompt_queue.wipe_history()
             if "delete" in json_data:
                 to_delete = json_data['delete']
                 for id_to_delete in to_delete:
-                    self.prompt_queue.history.pop(id_to_delete, None)
+                    self.prompt_queue.delete_history_item(id_to_delete)
 
             return web.Response(status=200)