Java memory model - can someone explain it?

Question

For years and years, I\'ve tried to understand the part of Java specification that deals with memory model and concurrency. I have to admit that I\'ve failed miserably. Yes\

Answer 1

• non-volatile variables can be cached thread-locally, so different threads may see different values at the same time; volatile prevents this (source)
• writes to variables of 32 bits or smaller are guaranteed to be atomic (implied here); not so for long and double, though 64bit JVMs probably implement them as atomic operations