Search code examples
javamultithreadingvolatilecpu-cache

Is volatile keyword of any use if I run the application in single core machine?

I have recently getting myself familiarized with volatile keyword and I see that not reading from main memory directly can result in inconsistency and the so-called visibility problem.

I believe the CPU cache is not specific to any thread. So I was wondering if the volatile keyword will be of any use in singlecore processor?

Solution

  • Hardware-level concurrency is obviously an important part of the motivation for the spec, but the spec is quite clear that the requirements apply to the system as a whole; so, for example, the JVM's "just-in-time" (JIT) compiler can legitimately optimize the equivalent of

    while (this.var) {
    ... code that provably never modifies var ...
}

    to the equivalent of

    if (this.var) {
    while (true) {
         ... code that provably never modifies var ...
    }
}

    if var is not volatile.