JAVA多線(xiàn)程編程核心技術(shù)--遇到的問(wèn)題

sleep(1)可以解決共享內(nèi)存的問(wèn)題

代碼

• 一個(gè)線(xiàn)程B寫(xiě)，一個(gè)線(xiàn)程A讀，在沒(méi)有volitile的情況下，如何停止線(xiàn)程A。
• ThreadB.java

package com;

public class ThreadB extends Thread {

    private MyList list;

    public ThreadB(MyList list) {
        this.list = list;
    }

    @Override
    public void run() {
        try {
            for (int i = 0; i < 10; i++) {
                list.add();
                System.out.println("添加了" + i + "個(gè)元素");
                Thread.sleep(1000);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

• TheadA.java

package com;

public class ThreadA extends Thread {

    private MyList list;

    public ThreadA(MyList list) {
        this.list = list;
    }

    @Override
    public void run() {
        try {
            while (true) {
                sleep(1);
                if (list.size() == 5) {
                    System.out.println("線(xiàn)程退出");
                    throw new InterruptedException();
                }
            }
        } catch (Exception e) {
            System.out.println("異常了");
            e.printStackTrace();
        }
    }
}

• MyList.java

package com;


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

public class MyList {
    private List<String> list = new ArrayList<String>();

    public void add() {
        list.add("畢玉強(qiáng)");
    }

    public int size() {
        return list.size();
    }
}

• Run.class

package com;

public class Run {

    public static void main(String[] args) {

        MyList myList = new MyList();
        ThreadA threadA = new ThreadA(myList);
        threadA.setName("a");
        ThreadB threadB = new ThreadB(myList);
        threadB.setName("b");
        threadB.start();
        threadA.start();

    }
}

問(wèn)題解釋

• 雖然沒(méi)有volitile,sleep(1)會(huì)引起上下文切換，將主內(nèi)存的數(shù)據(jù)重新加載到線(xiàn)程棧。
• 另外jvm會(huì)盡可能的將數(shù)據(jù)加載,到主內(nèi)存中，并且在主內(nèi)存讀讀取。
• System.out.PrintLn(" "),sychronized(list){},因?yàn)橛袀€(gè)this鎖，所以比較耗時(shí)，也符合上述條件。