可运行的非最终字段是否不安全以提交给执行者？

Question

If I have code like the following:

  public void foo() {
    Executors.newSingleThreadedExecutor().submit(
      new Runnable() {
        int x = 5;
        public void run() {
          System.out.println("x = " + x);
        }
      }
    );
  }

Am I guaranteed to see "x = 5", or could I also see "x = 0" because the println is being executed in a different thread that might see the uninitialized value of x ? I've never witnessed this happen, but I've been unable to find a guarantee that this doesn't happen (for example, if x were final , then it seems it will never happen).

Answer 1

There are a number of "happens before" relationships defined in the latest JMM. One of these points is "starting a thread" and submitting to an executor carries the same guarantees as starting a thread (see the "memory consistency effects" in the javadocs).