java - Java 中的 protected block 。我应该在哪里更新条件变量？

Question

我会使用 volatile 条件变量，但我认为 volatile 是多余的。此外，我不太确定我从https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/package-summary.html#MemoryVisibility中理解了这一点。正确的是:

An unlock (synchronized block or method exit) of a monitor happens-before every subsequent lock (synchronized block or method entry) of that same monitor. And because the happens-before relation is transitive, all actions of a thread prior to unlocking happen-before all actions subsequent to any thread locking that monitor.

因此随后调用同步 block 。但是，在 synchronized block 中执行的赋值结果对所有后续 synchronized block 可见吗？

这是一个示例应用程序。

package sample;

public class Foo {

    private boolean shouldWait;
    private final Object lock = new Object();

    void blockThread() {
        synchronized (lock) {
            shouldWait = true;
            while (shouldWait) {
                try {
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    void notifyThread() {
        synchronized (lock) {
            shouldWait = false;
            lock.notify();
        }
    }
}

测试。

package sample;

public class Main {

    private static Foo foo = new Foo();

    public static void main(String[] args) {
        new Thread(new Runnable() {

            @Override
            public void run() {
                foo.blockThread();
            }
        }).start();
        try {
            Thread.sleep(200);
        } catch (InterruptedException e) {
        }
        new Thread(new Runnable() {

            @Override
            public void run() {
                foo.notifyThread();
            }
        }).start();
    }

}

Answer 1

So synchronized blocks are called subsequently. But are results of assignments performed in a synchronized block visible to all the subsequent synchronized blocks?

是的。 volatile 写入具有相同的关系。 volatile 写入之前的所有操作都发生在所有后续读取之前。