Double checked locking Article

Question

I was reading this article about \"Double-Checked locking\" and out of the main topic of the article I was wondering why at some point of the article the author uses the nex

Answer 1

The point of locking twice was to attempt to prevent out-of-order writes. The memory model specifies where reorderings can occur, partly in terms of locks. The lock ensures that no writes (including any within the singleton constructor) appear to happen after the "instance = inst;" line.

However, to go deeper into the subject I'd recommend Bill Pugh's article. And then never attempt it :)