Does Java reordering affect System.currentTimeMillis()?

Question

According to Java Memory Model, instructions can be reordered as long as the execution is well-formed.

So I wonder, is it possible that the following codes produces the following output?

[codes][in a same thread]

long a = System.currentTimeMillis();
long b = System.currentTimeMillis();
long c = System.currentTimeMillis();

[output]

a == 10, b == 20, c == 15

If not possible, then what does JVM / implementations do to prevent this from happening?

Answer 1

Please see this question Instruction reordering & happens-before relationship in java.

I believe that unless you are in a different thread, the outcome of any execution will always be consistent with the order in your code. In this situation, since it is impossible to process it out of order, it should be good even if your fields are visible to another thread.