Question

最近我读过Bruce Eckel（Thinking in Java），我发现了一些问题：块同步（Object）锁定类！不是这个类的对象。上面提到的代码证明了这一点：

public class Main {

    public static void main(String[] args) {
        Sync s = new Sync();
        new Thread(new Runnable() {
            @Override
            public void run() {
                s.go();
            }
        }, "First").start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                s.go();
            }
        }, "Second").start();
    }
}

class Sync {

    private Writer w1, w2;

    public Sync() {
        w1 = new Writer();
        w2 = new Writer();
    }

    public void go() {
        synchronized (w2) {
            w1.log(Thread.currentThread().getName() + "...1");
            //!All threads must performance parallel, but they do it consistently.
            w2.log(Thread.currentThread().getName() + "...2");
            //All threads must performance parallel, and they do it.
        }
    }
}

class Writer {
    public void log(Object obj) {
        for (int i = 0; i < 5; i++) {
            lgn(obj);
            try {
                TimeUnit.MILLISECONDS.sleep(750);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

我锁定了w2，但锁定得到了w2，!! W1。为什么？ w1和w2是不同的对象！他们为什么要锁定在一起？

但所有来源都在讨论锁定同步的OBJECT，而不是Class！如果我误会了，你能帮我理解它是如何运作的吗？

输出

First...1
First...1
First...1
First...1
First...1
First...2
First...2
First...2
First...2
First...2
Second...1
Second...1
Second...1
Second...1
Second...1
Second...2
Second...2
Second...2
Second...2
Second...2

预期输出

First...1
Second...1
First...1
Second...1
First...1
Second...1
First...1
Second...1
First...1
Second...1
First...2
First...2
First...2
First...2
First...2
Second...2
Second...2
Second...2
Second...2
Second...2

P.S抱歉我的英语（

Answer 1

<uses-permission android:name="android.permission.INTERNET"/>表示我们用w2创建一个Lock，而不是锁定对象w2。您可以使用任何其他对象创建锁定，同步块中的代码仍然被锁定。

synchronized (w2)

Java同步锁定类，而不是对象？

1 个答案: