《Java多线程编程核心技术》读后感（七）

 

volatile关键字

　　主要作用是使变量在多个线程间可见。

关键字volatile与死循环

package Second;

public class PrintString {

    private boolean isContinuePrint = true;

    public boolean isContinuePrint() {
        return isContinuePrint;
    }

    public void setContinuePrint(boolean isContinuePrint) {
        this.isContinuePrint = isContinuePrint;
    }

    public void printStringMethod() {
        try {
            while (isContinuePrint == true) {
                System.out.println("run printStringMethod threadName="
                        + Thread.currentThread().getName());
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

package Second;

public class Run {

    public static void main(String[] args) {
        PrintString printStringService = new PrintString();
        printStringService.printStringMethod();
        System.out.println("我要停止它！stopThread="
                + Thread.currentThread().getName());
        printStringService.setContinuePrint(false);
    }

}

解决同步死循环

package Second;

public class PrintString implements Runnable {

    private boolean isContinuePrint = true;

    public boolean isContinuePrint() {
        return isContinuePrint;
    }

    public void setContinuePrint(boolean isContinuePrint) {
        this.isContinuePrint = isContinuePrint;
    }

    public void printStringMethod() {
        try {
            while (isContinuePrint == true) {
                System.out.println("run printStringMethod threadName="
                        + Thread.currentThread().getName());
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public void run() {
        printStringMethod();
    }
}

package Second;

public class Run {

    public static void main(String[] args) {
        PrintString printStringService = new PrintString();
        new Thread(printStringService).start();

        System.out.println("我要停止它！stopThread="
                + Thread.currentThread().getName());
        printStringService.setContinuePrint(false);
    }

}

关键字volatile的作用是强制从公共堆栈中取得变量的值，而不是从线程私有数据栈中取得变量的值

 解决异常死循环

package Second;

public class RunThread extends Thread {

    private boolean isRunning = true;

    public boolean isRunning() {
        return isRunning;
    }

    public void setRunning(boolean isRunning) {
        this.isRunning = isRunning;
    }

    @Override
    public void run() {
        System.out.println("进入run了");
        while (isRunning == true) {
        }
        System.out.println("线程被停止了！");
    }

}

package Second;

public class Run {
    public static void main(String[] args) {
        try {
            RunThread thread = new RunThread();
            thread.start();
            Thread.sleep(1000);
            thread.setRunning(false);
            System.out.println("已经赋值为false");
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

package Second;

public class RunThread extends Thread {

    volatile private boolean isRunning = true;

    public boolean isRunning() {
        return isRunning;
    }

    public void setRunning(boolean isRunning) {
        this.isRunning = isRunning;
    }

    @Override
    public void run() {
        System.out.println("进入run了");
        while (isRunning == true) {
        }
        System.out.println("线程被停止了！");
    }

}

volitile非原子特性

package Second;

public class MyThread extends Thread {
    volatile public static int count;

    private static void addCount() {
        for (int i = 0; i < 100; i++) {
            count++;
        }
        System.out.println("count=" + count);
    }

    @Override
    public void run() {
        addCount();
    }

}

package Second;

public class Run {
    public static void main(String[] args) {
        MyThread[] mythreadArray = new MyThread[100];
        for (int i = 0; i < 100; i++) {
            mythreadArray[i] = new MyThread();
        }

        for (int i = 0; i < 100; i++) {
            mythreadArray[i].start();
        }

    }

}

package Second;

public class MyThread extends Thread {
    public static int count;

    synchronized private static void addCount() {
        for (int i = 0; i < 100; i++) {
            count++;
        }
        System.out.println("count=" + count);
    }

    @Override
    public void run() {
        addCount();
    }

}

使用原子类进行i++操作（详见书）

原子类也并不完全安全（详见书）

synchronized代码块有volatile同步的功能 

package Second;

public class Service {

    private boolean isContinueRun = true;

    public void runMethod() {
        String anyString = new String();
        while (isContinueRun == true) {
          
        }
        System.out.println("停下来了！");
    }

    public void stopMethod() {
        isContinueRun = false;
    }
}

package Second;

public class ThreadA extends Thread {
    private Service service;

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

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

package Second;

public class ThreadB extends Thread {
    private Service service;

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

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

}

package Second;

public class Run {

    public static void main(String[] args) {
        try {
            Service service = new Service();

            ThreadA a = new ThreadA(service);
            a.start();

            Thread.sleep(1000);

            ThreadB b = new ThreadB(service);
            b.start();

            System.out.println("已经发起停止的命令了！");
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

package Second;

public class Service {

    private boolean isContinueRun = true;

    public void runMethod() {
        String anyString = new String();
        while (isContinueRun == true) {
            synchronized (anyString) {
            }
        }
        System.out.println("停下来了！");
    }

    public void stopMethod() {
        isContinueRun = false;
    }
}