Learn→Classical Synchronization Problems→Thread-Safe Singleton & Double-Checked Locking→6 of 6

Classical Synchronization Problems • Thread-Safe Singleton & Double-Checked LockingMedium⏱️ ~2 min

When to Use Which Approach

Decision Guide
The right approach depends on your language, whether you need lazy initialization, and how much control over timing you need.
Use Eager Initialization When
The singleton is always needed. The cost of creation is low. You want simplicity. Class loading guarantees thread safety. No volatile, no DCL, no complexity.
Use Holder Pattern (Java) When
You want lazy initialization without synchronization overhead. The singleton might not be used in every execution path. This is the sweet spot for most Java applications.
Decision Matrix
Eager InitSimple, always usedHolder PatternLazy, Java onlyEnum SingletonBulletproof, JavaDCLMax control, riskyStatic Local (C++)Simple, C++11+std::call_onceExplicit, C++
Use Enum Singleton (Java) When
You need protection against serialization and reflection attacks. You want the simplest possible implementation. The singleton does not need to extend another class.
Use DCL When
You need maximum control over initialization timing. You are working in a language without better alternatives. You understand the memory model implications. In practice, this is rare.
Use Static Local (C++11+) When
You are writing modern C++. You want lazy initialization. You want the compiler to handle synchronization. This is the default choice for C++ singletons today.
Bottom Line: In Java, use holder pattern or enum. In C++11+, use static local. DCL is for interviews and edge cases. Simpler is almost always better.

💡 Key Takeaways

✓Eager initialization: simplest, for always-used singletons with low creation cost. No synchronization needed.

✓Holder pattern (Java): lazy, zero overhead after init. Best general-purpose choice for Java singletons.

✓Enum singleton (Java): bulletproof against serialization and reflection. Limited by enum constraints (no inheritance).

✓DCL: maximum control, maximum risk. Use only when you need precise control over initialization timing.

✓Static local (C++11): simple and safe. Compiler handles synchronization. Default choice for modern C++.

📌 Examples

1Logger singleton: always used, cheap to create. Eager initialization is perfect - no reason to delay.

2Database connection pool: expensive to create, might not be needed in test scenarios. Holder pattern or lazy init.

3Security manager needing reflection protection: enum singleton prevents malicious instantiation attempts.

← Back to Thread-Safe Singleton & Double-Checked Locking Overview