synchronized同步语句块

Z时代
2024-01-10
分类：综合

public class ObjectService {
    public void serviceMethod() {
        try {
            synchronized (this) {
                System.out.println("begin time = " + System.currentTimeMillis());
                Thread.sleep(2000);
                System.out.println("end   time = " + System.currentTimeMillis());
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class ThreadA extends Thread {
    private ObjectService service;
    public ThreadA(ObjectService service) {
        this.service = service;
    }
    @Override
    public void run() {
        super.run();
        service.serviceMethod();
    }
}

public class ThreadB extends Thread {
    private ObjectService service;
    public ThreadB(ObjectService service) {
        this.service = service;
    }
    @Override
    public void run() {
        super.run();
        service.serviceMethod();
    }
}

public class Run {
    public static void main(String[] args) {
        ObjectService service = new ObjectService();
        ThreadA aThread = new ThreadA(service);
        ThreadB bThread = new ThreadB(service);
        aThread.setName("a");
        bThread.setName("b");
        aThread.start();
        bThread.start();
    }
}

一半异步，一半同步

不在synchronized块中就是异步执行，在synchronized块中就是同步执行。

public class Task {
    public void doLongTimeTask() {
        for (int i = 0; i < 100; i++) {
            System.out.println("no synchronized thread name = " + Thread.currentThread().getName() + " i = " + (i + 1));
        }
        System.out.println();
        synchronized (this) {
            for (int i = 0; i < 100; i++) {
                System.out.println("synchronized thread name = " + Thread.currentThread().getName() + " i = " + (i + 1));
            }
        }
    }
}

synchronized代码块间的同步性

在使用synchronized（this）代码块需要注意的是，当一个线程访问object的一个synchronized（this）同步代码块时，其他线程对同一个object中所有其他synchronized（this）同步代码块的访问将被阻塞，这说明synchronized使用的“对象监视器”是一个。

public class ObjectService {
    public void serviceMethodA() {
        try {
            synchronized (this) {
                System.out.println("A begin time = " + System.currentTimeMillis());
                Thread.sleep(2000);
                System.out.println("A   end time = " + System.currentTimeMillis());
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public void serviceMethodB() {
        synchronized (this) {
            System.out.println("B begin time = " + System.currentTimeMillis());
            System.out.println("B   end time = " + System.currentTimeMillis());
        }
    }
}

public class ThreadA extends Thread {
    private ObjectService service;
    public ThreadA(ObjectService service) {
        this.service = service;
    }
    @Override
    public void run() {
        super.run();
        service.serviceMethodA();
    }
}

public class ThreadB extends Thread {
    private ObjectService service;
    public ThreadB(ObjectService service) {
        this.service = service;
    }
    @Override
    public void run() {
        super.run();
        service.serviceMethodB();
    }
}

public class Run {
    public static void main(String[] args) {
        ObjectService service = new ObjectService();
        ThreadA aThread = new ThreadA(service);
        ThreadB bThread = new ThreadB(service);
        aThread.setName("a");
        aThread.start();
        bThread.setName("b");
        bThread.start();
    }
}