synchronized 同步，解決多執行緒 訪問臨界區的問題，作用於例項 ，但是 修飾 static 方法 是 作用.class 鎖

volatile 變數的執行緒可見，換句不太恰當的話，就是扔在了執行緒棧外（共享區域）

volatile 例項1，這裡有個坑 while(flag)  會被jvm 優化 成 if(flag){ while(true){} }　 (坑)　

package Concurrency;

public class volatile1 extends Thread {
    private volatile boolean
 
 flag = true;
    public void run(){
        while(this.flag == true){
        }
        System.out.println("出來了");
    }
    public void setFlag(boolean flag){
        this.flag = flag;
    }
    public static   void main(String []arg)throws InterruptedException
    {
        volatile1 v = new volatile1();
        v.start();;
        Thread.sleep(
 
1000);
        v.setFlag(false);
        Thread.sleep(2000);
        System.out.println("Main 走了");
    }
}

重入問題 ，那個準則，不要進行 申請記憶體，靜態地址，非重入函式，（剩下的重入鎖 學到再說）

多執行緒重入

package Concurrency;

public class syncDubbo1 {
    public synchronized  void func1(){
        System.out.println(
 
"Func1");
        func2();
    }
    public synchronized  void func2(){
        System.out.println("func2");
        func3();
    }
    public synchronized  void func3(){
        System.out.println("func3");
    }


    public static void main(String []arg){
        syncDubbo1 s = new syncDubbo1();
        Thread t1 =new Thread(new Runnable() {
            @Override
            public void run() {
                s.func1();
            }
        });
        t1.start();

        s.func2();

    }
}

父子類的重入

package Concurrency;

import java.util.concurrent.SubmissionPublisher;

public class syncDubbo2 {
    static class Father{
        static int i =10;
        public synchronized void operator(){
            i--;
            try {
                System.out.println("Father sub Num "+i);
                Thread.sleep(100);
            }catch (InterruptedException e){
                e.printStackTrace();;
            }
        }
    }
    static class Sub extends Father{
        @Override
        public synchronized void operator(){
            while(i>0)
            {
                i--;
                try {
                    System.out.println("Son  sub Num "+i);
                    Thread.sleep(100);
                    super.operator();
                }catch (InterruptedException e){
                    e.printStackTrace();;
                }
            }
        }
    }
    public static void  main(String []arg){
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                Sub s =  new Sub();
                s.operator();
            }
        });
        t1.start();
    }
}