class_docstr: This is a thread-safe implementation of Singleton.
code: def __call__(cls, uri):
      key = (cls, uri)
      with cls._lock:
          if key not in cls._instances:
              instance = super().__call__(uri)
              cls._instances[key] = instance
      return cls._instances[key]
  
file_path: evadb/evadb/catalog/sql_config.py
imports: from threading import Lock
  from weakref import WeakValueDictionary
  from sqlalchemy import create_engine, event
  from sqlalchemy.orm import scoped_session, sessionmaker
label_desc: Use image node_id 1 for calling the SingletonMeta obj's underlying member method code with example usage: obj.__call__(cls, uri) and returns: cls