It's well-known that you can do double-checked locking right with memory barriers, but memory barriers aren't always cheaper. On TSO architectures (x86, most SP

It's well-known that you can do double-checked locking right with memory barriers, but memory barriers aren't always cheaper. On TSO architectures (x86, most SPARCs), read barriers are no-ops, but with weaker memory models (e.g., ARM), they aren't. Edit: Also, the memory barriers are in the wrong place in the code. You need a read barrier between the init check and returning ptr, and a write barrier between the actual initialization of the object and writing the init variable.