customserver: fix memory leak (#3864)

MultiServer.py

@@ -67,6 +67,21 @@ def update_dict(dictionary, entries):
     return dictionary
 
 
+def queue_gc():
+    import gc
+    from threading import Thread
+
+    gc_thread: typing.Optional[Thread] = getattr(queue_gc, "_thread", None)
+    def async_collect():
+        time.sleep(2)
+        setattr(queue_gc, "_thread", None)
+        gc.collect()
+    if not gc_thread:
+        gc_thread = Thread(target=async_collect)
+        setattr(queue_gc, "_thread", gc_thread)
+        gc_thread.start()
+
+
 # functions callable on storable data on the server by clients
 modify_functions = {
     # generic:
@@ -551,6 +566,9 @@ class Context:
                         self.logger.info(f"Saving failed. Retry in {self.auto_save_interval} seconds.")
                     else:
                         self.save_dirty = False
+                if not atexit_save:  # if atexit is used, that keeps a reference anyway
+                    queue_gc()
+
             self.auto_saver_thread = threading.Thread(target=save_regularly, daemon=True)
             self.auto_saver_thread.start()