Consider the following simple Java application:

public class Main {
    public int a;
    public volatile int b;

    public void thread1(){
        int b;
        a = 1;
        b = this.b;
    }

    public void thread2(){
        int a;
        b = 1;
        a = this.a;
    }

    public static void main(String[] args) throws Exception {
        Main m = new Main();
        while(true){
            m.a = 0;
            m.b = 0;
            Thread t1 = new Thread(() -> m.thread1());
            Thread t2 = new Thread(() -> m.thread2());
            t1.start();
            t2.start();
            t1.join();
            t2.join();
        }
    }
}

QUESTION: Is it possible that reading into local variables will result in thread1::b = 0 and thread2::a = 0?

I could not prove that it could not happen from the JMM standpoint so I went down to analyzing compiled code for x86-64.

Here is what compiler ends up with for methods thread1 and thread2 (code unrelated to the while loop and some comments generated by -XX: PrintAssembly omitted for simplicity):

thread1:

  0x00007fb030dca235: movl    $0x1,0xc(%rsi)    ;*putfield a
  0x00007fb030dca23c: mov     0x10(%rsi),%esi   ;*getfield b

thread2:

  0x00007fb030dcc1b4: mov     $0x1,