《Java多线程编程核心技术》读后感（六）

 

多线程的死锁

package Second;

public class DealThread implements Runnable {

    public String username;
    public Object lock1 = new Object();
    public Object lock2 = new Object();

    public void setFlag(String username) {
        this.username = username;
    }

    @Override
    public void run() {
        if (username.equals("a")) {
            synchronized (lock1) {
                try {
                    System.out.println("username = " + username);
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                synchronized (lock2) {
                    System.out.println("按lock1->lock2代码顺序执行了");
                }
            }
        }
        if (username.equals("b")) {
            synchronized (lock2) {
                try {
                    System.out.println("username = " + username);
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                synchronized (lock1) {
                    System.out.println("按lock2->lock1代码顺序执行了");
                }
            }
        }
    }

}

只要互相等待对方释放锁就有可能出现死锁

内置类与静态内置类

package Second;

public class PublicClass {

    private String username;
    private String password;

    class PrivateClass {
        private String age;
        private String address;

        public String getAge() {
            return age;
        }

        public void setAge(String age) {
            this.age = age;
        }

        public String getAddress() {
            return address;
        }

        public void setAddress(String address) {
            this.address = address;
        }

        public void printPublicProperty() {
            System.out.println(username + " " + password);
        }
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

}

package Second;

import Second.PublicClass.PrivateClass;

public class Run {

    public static void main(String[] args) {

        PublicClass publicClass = new PublicClass();
        publicClass.setUsername("usernameValue");
        publicClass.setPassword("passwordValue");

        System.out.println(publicClass.getUsername() + " "
                + publicClass.getPassword());

        PrivateClass privateClass = publicClass.new PrivateClass();
        privateClass.setAge("ageValue");
        privateClass.setAddress("addressValue");

        System.out.println(privateClass.getAge() + " "
                + privateClass.getAddress());

    }

}

package Second;

public class PublicClass {

    static private String username;
    static private String password;

    static class PrivateClass {
        private String age;
        private String address;

        public String getAge() {
            return age;
        }

        public void setAge(String age) {
            this.age = age;
        }

        public String getAddress() {
            return address;
        }

        public void setAddress(String address) {
            this.address = address;
        }

        public void printPublicProperty() {
            System.out.println(username + " " + password);
        }
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

}

package Second;

import Second.PublicClass.PrivateClass;

public class Run {

    public static void main(String[] args) {

        PublicClass publicClass = new PublicClass();
        publicClass.setUsername("usernameValue");
        publicClass.setPassword("passwordValue");

        System.out.println(publicClass.getUsername() + " "
                + publicClass.getPassword());

        PrivateClass privateClass = new PrivateClass();
        privateClass.setAge("ageValue");
        privateClass.setAddress("addressValue");

        System.out.println(privateClass.getAge() + " "
                + privateClass.getAddress());

    }

}

内置类与同步：实验1

本实验案例是在内置类中有两个同步方法，但使用的却是不同的锁，打印的结果也是异步的。

package Second;

public class OutClass {

    static class Inner {
        public void method1() {
            synchronized ("其他的鎖") {
                for (int i = 1; i <= 10; i++) {
                    System.out.println(Thread.currentThread().getName() + " i="
                            + i);
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                    }
                }
            }
        }

        public synchronized void method2() {
            for (int i = 11; i <= 20; i++) {
                System.out.println(Thread.currentThread().getName() + " i=" + i);
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                }
            }
        }
    }
}

package Second;

import Second.OutClass.Inner;

public class Run {
    public static void main(String[] args) {

        final Inner inner = new Inner();

        Thread t1 = new Thread(new Runnable() {
            public void run() {
                inner.method1();
            }
        }, "A");

        Thread t2 = new Thread(new Runnable() {
            public void run() {
                inner.method2();
            }
        }, "B");

        t1.start();
        t2.start();

    }
}

由于持有不同的“”对象监视器“”，所以打印结果就是乱序的

内置类与同步：实验2

锁对象的改变

package Second;

public class MyService {
    private String lock = "123";

    public void testMethod() {
        try {
            synchronized (lock) {
                System.out.println(Thread.currentThread().getName() + " begin "
                        + System.currentTimeMillis());
                lock = "456";
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName() + "   end "
                        + System.currentTimeMillis());
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

package Second;

public class ThreadA extends Thread {

    private MyService service;

    public ThreadA(MyService service) {
        super();
        this.service = service;
    }

    @Override
    public void run() {
        service.testMethod();
    }
}

package Second;

public class ThreadB extends Thread {

    private MyService service;

    public ThreadB(MyService service) {
        super();
        this.service = service;
    }

    @Override
    public void run() {
        service.testMethod();
    }
}

package Second;

public class Run1 {

    public static void main(String[] args) throws InterruptedException {

        MyService service = new MyService();

        ThreadA a = new ThreadA(service);
        a.setName("A");

        ThreadB b = new ThreadB(service);
        b.setName("B");

        a.start();
        Thread.sleep(50);
        b.start();
    }
}

因为50毫秒过后线程B获得的锁时“”456“”

package Second;

public class Run2 {

    public static void main(String[] args) throws InterruptedException {

        MyService service = new MyService();

        ThreadA a = new ThreadA(service);
        a.setName("A");

        ThreadB b = new ThreadB(service);
        b.setName("B");

        a.start();
        b.start();
    }
}

线程AB持有的锁都是“”123“”，虽然将锁改成了“”456“”，但结果还是同步的，因为A和B共同争抢的锁时“”123“”

package Second;

public class Userinfo {
    private String username;
    private String password;

    public Userinfo() {
        super();
    }

    public Userinfo(String username, String password) {
        super();
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

}

package Second;

public class Service {

    public void serviceMethodA(Userinfo userinfo) {
        synchronized (userinfo) {
            try {
                System.out.println(Thread.currentThread().getName());
                userinfo.setUsername("abcabcabc");
                Thread.sleep(3000);
                System.out.println("end! time=" + System.currentTimeMillis());
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

package Second;

public class ThreadA extends Thread {

    private Service service;
    private Userinfo userinfo;

    public ThreadA(Service service, 
            Userinfo userinfo) {
        super();
        this.service = service;
        this.userinfo = userinfo;
    }

    @Override
    public void run() {
        service.serviceMethodA(userinfo);
    }

}

package Second;

public class ThreadB extends Thread {

    private Service service;
    private Userinfo userinfo;

    public ThreadB(Service service, 
            Userinfo userinfo) {
        super();
        this.service = service;
        this.userinfo = userinfo;
    }

    @Override
    public void run() {
        service.serviceMethodA(userinfo);
    }

}

package Second;

public class Run {

    public static void main(String[] args) {

        try {
            Service service = new Service();
            Userinfo userinfo = new Userinfo();

            ThreadA a = new ThreadA(service, userinfo);
            a.setName("a");
            a.start();
            Thread.sleep(50);
            ThreadB b = new ThreadB(service, userinfo);
            b.setName("b");
            b.start();

        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}

上述实验表明：只要对象不变，即使对象的属性被改变，运行的结果还是同步。