In Java, updating double and long variable may not be atomic, as double/long are being treated as two separate 32 bits variables.

http://java.sun.com/docs/books/jls/second_edition/html/memory.doc.html#28733

In C++, if I am using 32 bit Intel Processor + Microsoft Visual C++ compiler, is updating double (8 byte) operation atomic?

I cannot find much specification mention on this behavior.

When I say "atomic variable", here is what I mean :

Thread A trying to write 1 to variable x. Thread B trying to write 2 to variable x.

We shall get value 1 or 2 out from variable x, but not an undefined value.