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28 lines
921 B
28 lines
921 B
import threading
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class SingletonMeta(type):
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"""
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Thread-safe Singleton Meta with double-checked locking.
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Reference: https://en.wikipedia.org/wiki/Double-checked_locking
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"""
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_instances = {}
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_lock = threading.Lock()
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def __call__(cls, *args, **kwargs):
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# First check (without locking) for performance reasons
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if cls not in cls._instances:
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# Acquire a lock before proceeding to the second check
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with cls._lock:
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# Second check with lock held to ensure thread safety
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if cls not in cls._instances:
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instance = super().__call__(*args, **kwargs)
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cls._instances[cls] = instance
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else:
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assert (
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len(args) == 0 and len(kwargs) == 0
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), f"{cls.__name__} is a singleton class and an instance has been created."
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return cls._instances[cls]
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