Both the compiler and CPU will reorder operations. Proper locking requires a memory barrier which will prevent both CPU and compiler from doing that. For more

Both the compiler and CPU will reorder operations. Proper locking requires a memory barrier which will prevent both CPU and compiler from doing that. For more information I recommend reading up on double checked locking. DDJ had a good pair of articles the first where they presented the faulty algorithm, the second where they talked about why it was broken. C/c++ doesn't have many guarantees about operation ordering. http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLo...