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Dp Multiton

DodaTech 1 min read

In this tutorial, you'll learn about How to Fix Multiton Errors. We cover key concepts, practical examples, and best practices.

Fix multiton errors when multiple named instances not key-managed or global dict polluted.

Quick Fix

Wrong

class Config:
    _instances={}
    @classmethod
    def get(cls,name):
        if name not in cls._instances:
            cls._instances[name]=cls._load(name)
        return cls._instances[name]
    @classmethod
    def _load(cls,name):
        print(f'Loading {name}')
        return cls()

Thread safety not ensured. Two threads may load same config simultaneously.

import threading
class Config:
    _instances={}; _lock=threading.Lock()
    @classmethod
    def get(cls,name):
        if name not in cls._instances:
            with cls._lock:
                if name not in cls._instances:
                    cls._instances[name]=cls._load(name)
        return cls._instances[name]
    @classmethod
    def _load(cls,name):
        print(f'Loading {name}'); return cls()
c1=Config.get('dev'); c2=Config.get('prod'); c3=Config.get('dev'); c1 is c3 -> True

Named instances cached. Thread-safe double-checked locking. Each key has one instance.

Prevention

Multiton ensures unique instance per key. Thread-safe registration.

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FAQ

What is Multiton?

Singleton per key. Guarantees one instance per identifier.

When to use?

Named configurations, per-database connections, per-tenant services.

vs Singleton?

Singleton: one globally. Multiton: one per key (registry pattern).

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