Is Meyer's Singleton Implementation Truly a Singleton, and How Does it Compare to Thread-Safe Alternatives?

Meyer's Implementation: Exploring the True Singleton Nature

The Meyer's Singleton implementation, presented as static Singleton& instance(), raises questions regarding its singleton functionality.

Enforcement of Singleton Pattern

The singleton nature stems from the static keyword. Static storage duration for local variables means only one instance exists throughout the program.

Consider this equivalent pseudocode (not actual C 98 code):

static bool __guard = false;
static char __storage[sizeof(Singleton)];

Singleton& Instance() {
  if (!__guard ) {
    __guard = true;
    new (__storage) Singleton();
  }
  return *reinterpret_cast<Singleton*&>(__storage);
}

This roughly encapsulates the behavior of the original implementation.

Thread Safety Considerations

In the actual C 11 implementation, a guard variable is used for each static, acting as a barrier for threads.

Implementation Comparison

Both implementations enforce singleton integrity, but differ in thread handling and code complexity.

• Meyer's Implementation:

  • Simpler code
  • May require additional synchronization mechanisms for multithreading

• Wikipedia Implementation:

  • More complex code
  • Provides built-in thread safety

Conclusion

The Meyer's implementation is indeed a Singleton due to the static storage duration preventing multiple instantiations. The choice between the two implementations depends on the specific application and multithreading considerations.

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