多線程學習筆記(七)

時間 2019-11-07

標籤多線程學習筆記欄目 Java 简体版

原文原文鏈接

在使用synchronized時,當一個線程獲得一個對象鎖後,再次請求此對象鎖時是能夠再次獲得該對象鎖的.這也證實在一個synchronized方法/塊的內部調用本類的其餘synchronized方法/塊時,是永遠能夠獲得鎖的.ide

public class ThreadReenter {
    synchronized public void firstService() {
        System.out.println("This is the first service!");
        secondService();
    }

    synchronized public void secondService() {
        System.out.println("This is the second service!");
        thirdService();
    }

    synchronized public void thirdService() {
        System.out.println("This is the third service!");
    }
}

public class FirstThread extends Thread {

    @Override
    public void run(){
        ThreadReenter threadReenter = new ThreadReenter();
        threadReenter.firstService();
    }
}

public class Run {
    public static void main(String[] args) {
        FirstThread firstThread = new FirstThread();
        firstThread.start();

    }
}

運行結果:this

可重入鎖的概念:線程

本身能夠再次獲取本身的內部鎖.好比一個線程獲取了某個對象的鎖,此時這個對象的鎖尚未釋放,當這個線程想要獲取這個對象的鎖的時候仍是能夠獲取的,若是不能夠鎖重入的話,就會形成死鎖.對象

注:可重入鎖也適用於父子類繼承的環境中.繼承

public class ThreadReenter {
    public int i = 10;
    synchronized public void ancestor(){
        try{
            i--;
            System.out.println("the ancestor i = " + i);
            Thread.sleep(200);
        }catch (Exception e){
            e.printStackTrace();
        }
    }

}

public class SonOfThreadReenter extends ThreadReenter{
    synchronized public void Posterity(){
        try{
            while(i > 0){
                i--;
                System.out.println("the Posterity i = " + i);
                Thread.sleep(200);
                this.ancestor();
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

public class FirstThread extends Thread {

    @Override
    public void run(){
        SonOfThreadReenter sonOfThreadReenter = new SonOfThreadReenter();
        sonOfThreadReenter.Posterity();
    }
}

public class Run {
    public static void main(String[] args) {
        FirstThread firstThread = new FirstThread();
        firstThread.start();

    }
}

運行結果:同步

當存在父子類繼承時,子類是徹底能夠經過可重入鎖調用父類的同步方法的.it