《Java多线程编程核心技术》读后感（十）

一生产一消费：操作栈

本实例是使生产者向堆栈List对象中放入数据，使消费者从List堆栈中取出数据。List最大容量是1

package Third;

import java.util.ArrayList;
import java.util.List;

public class MyStack {
    private List list = new ArrayList();

    synchronized public void push() {
        try {
            if (list.size() == 1) {
                this.wait();
            }
            list.add("anyString=" + Math.random());
            this.notify();
            System.out.println("push=" + list.size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    synchronized public String pop() {
        String returnValue = "";
        try {
            if (list.size() == 0) {
                System.out.println("pop操作中的："
                        + Thread.currentThread().getName() + " 线程呈wait状态");
                this.wait();
            }
            returnValue = "" + list.get(0);
            list.remove(0);
            this.notify();
            System.out.println("pop=" + list.size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return returnValue;
    }
}

package Third;

public class P_Thread extends Thread {

    private P p;

    public P_Thread(P p) {
        super();
        this.p = p;
    }

    @Override
    public void run() {
        while (true) {
            p.pushService();
        }
    }

}

package Third;

public class C_Thread extends Thread {

    private C r;

    public C_Thread(C r) {
        super();
        this.r = r;
    }

    @Override
    public void run() {
        while (true) {
            r.popService();
        }
    }

}

package Third;

public class P {

    private MyStack myStack;

    public P(MyStack myStack) {
        super();
        this.myStack = myStack;
    }

    public void pushService() {
        myStack.push();
    }
}

package Third;

public class C {

    private MyStack myStack;

    public C(MyStack myStack) {
        super();
        this.myStack = myStack;
    }

    public void popService() {
        System.out.println("pop=" + myStack.pop());
    }
}

package Third;

public class Run {
    public static void main(String[] args) {
        MyStack myStack = new MyStack();

        P p = new P(myStack);
        C r = new C(myStack);

        P_Thread pThread = new P_Thread(p);
        C_Thread rThread = new C_Thread(r);
        pThread.start();
        rThread.start();
    }

}

程序运行的结果是size（）不会大于1

一生产多消费-操作栈:解决wait条件改变与假死

上述代码只需要更改run.java

package Third;

public class Run {
    public static void main(String[] args) throws InterruptedException {
        MyStack myStack = new MyStack();

        P p = new P(myStack);

        C r1 = new C(myStack);
        C r2 = new C(myStack);
        C r3 = new C(myStack);
        C r4 = new C(myStack);
        C r5 = new C(myStack);

        P_Thread pThread = new P_Thread(p);
        pThread.start();

        C_Thread cThread1 = new C_Thread(r1);
        C_Thread cThread2 = new C_Thread(r2);
        C_Thread cThread3 = new C_Thread(r3);
        C_Thread cThread4 = new C_Thread(r4);
        C_Thread cThread5 = new C_Thread(r5);
        cThread1.start();
        cThread2.start();
        cThread3.start();
        cThread4.start();
        cThread5.start();
    }

}

问题的出现是因为在Mystack.java类中使用了if语句作为条件判断。因为条件发生改变时并没有及时的相应，所以多个呈wait状态的线程被唤醒，继而执行list.remove(0)代码而出现异常。解决这个办法是，将if改成while

package Third;

import java.util.ArrayList;
import java.util.List;

public class MyStack {
    private List list = new ArrayList();

    synchronized public void push() {
        try {
            while (list.size() == 1) {
                this.wait();
            }
            list.add("anyString=" + Math.random());
            this.notify();
            System.out.println("push=" + list.size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    synchronized public String pop() {
        String returnValue = "";
        try {
            while (list.size() == 0) {
                System.out.println("pop操作中的："
                        + Thread.currentThread().getName() + " 线程呈wait状态");
                this.wait();
            }
            returnValue = "" + list.get(0);
            list.remove(0);
            this.notify();
            System.out.println("pop=" + list.size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return returnValue;
    }
}

出现了假死状态，解决办法是notifyAll()

多生产与一消费：操作栈

package Third;

public class Run {
    public static void main(String[] args) throws InterruptedException {
        MyStack myStack = new MyStack();

        P p1 = new P(myStack);
        P p2 = new P(myStack);
        P p3 = new P(myStack);
        P p4 = new P(myStack);
        P p5 = new P(myStack);
        P p6 = new P(myStack);

        P_Thread pThread1 = new P_Thread(p1);
        P_Thread pThread2 = new P_Thread(p2);
        P_Thread pThread3 = new P_Thread(p3);
        P_Thread pThread4 = new P_Thread(p4);
        P_Thread pThread5 = new P_Thread(p5);
        P_Thread pThread6 = new P_Thread(p6);
        pThread1.start();
        pThread2.start();
        pThread3.start();
        pThread4.start();
        pThread5.start();
        pThread6.start();

        C c1 = new C(myStack);
        C_Thread cThread = new C_Thread(c1);
        cThread.start();

    }

}

多生产与多消费：操作栈

package Third;

public class Run {
    public static void main(String[] args) throws InterruptedException {
        MyStack myStack = new MyStack();

        P p1 = new P(myStack);
        P p2 = new P(myStack);
        P p3 = new P(myStack);
        P p4 = new P(myStack);
        P p5 = new P(myStack);
        P p6 = new P(myStack);

        P_Thread pThread1 = new P_Thread(p1);
        P_Thread pThread2 = new P_Thread(p2);
        P_Thread pThread3 = new P_Thread(p3);
        P_Thread pThread4 = new P_Thread(p4);
        P_Thread pThread5 = new P_Thread(p5);
        P_Thread pThread6 = new P_Thread(p6);
        pThread1.start();
        pThread2.start();
        pThread3.start();
        pThread4.start();
        pThread5.start();
        pThread6.start();

        C r1 = new C(myStack);
        C r2 = new C(myStack);
        C r3 = new C(myStack);
        C r4 = new C(myStack);
        C r5 = new C(myStack);
        C r6 = new C(myStack);
        C r7 = new C(myStack);
        C r8 = new C(myStack);

        C_Thread cThread1 = new C_Thread(r1);
        C_Thread cThread2 = new C_Thread(r2);
        C_Thread cThread3 = new C_Thread(r3);
        C_Thread cThread4 = new C_Thread(r4);
        C_Thread cThread5 = new C_Thread(r5);
        C_Thread cThread6 = new C_Thread(r6);
        C_Thread cThread7 = new C_Thread(r7);
        C_Thread cThread8 = new C_Thread(r8);

        cThread1.start();
        cThread2.start();
        cThread3.start();
        cThread4.start();
        cThread5.start();
        cThread6.start();
        cThread7.start();
        cThread8.start();

    }

}

通过管道进行线程间通信：字节流（见书）

通过管道进行线程间通信：字符流（见书）

实战：等待/通知之交叉备份

package Third;

public class DBTools {

    volatile private boolean prevIsA = false;

    synchronized public void backupA() {
        try {
            while (prevIsA == true) {
                wait();
            }
            for (int i = 0; i < 5; i++) {
                System.out.println("★★★★★");
            }
            prevIsA = true;
            notifyAll();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    synchronized public void backupB() {
        try {
            while (prevIsA == false) {
                wait();
            }
            for (int i = 0; i < 5; i++) {
                System.out.println("☆☆☆☆☆");
            }
            prevIsA = false;
            notifyAll();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

package Third;

public class BackupA extends Thread {

    private DBTools dbtools;

    public BackupA(DBTools dbtools) {
        super();
        this.dbtools = dbtools;
    }

    @Override
    public void run() {
        dbtools.backupA();
    }

}

package Third;

public class BackupB extends Thread {

    private DBTools dbtools;

    public BackupB(DBTools dbtools) {
        super();
        this.dbtools = dbtools;
    }

    @Override
    public void run() {
        dbtools.backupB();
    }

}

package Third;

public class Run {

    public static void main(String[] args) {
        DBTools dbtools = new DBTools();
        for (int i = 0; i < 20; i++) {
            BackupB output = new BackupB(dbtools);
            output.start();
            BackupA input = new BackupA(dbtools);
            input.start();
        }
    }

}