死鎖示例

由于兩個鎖對象lock1,lock2是static只存在一份,導致兩個線程執行時會相互等待已經被獲得的瑣對象,導致死鎖產生.
如果將static去掉,2個鎖對象就是線程獨有的變量,不會被別的線程發現,因此不會產生死鎖.

public class DeadLock implements Runnable{
    private String tag;
    private static Object lock1 = new Object();
    private static Object lock2 = new Object();
    
    public void setTag(String tag){
        this.tag = tag;
    }
    
    @Override
    public void run() {
        if(tag.equals("a")){
            synchronized (lock1) {
                try {
                    System.out.println("當前線程 : "  + Thread.currentThread().getName() + " 進入lock1執行");
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (lock2) {
                    System.out.println("當前線程 : "  + Thread.currentThread().getName() + " 進入lock2執行");
                }
            }
        }
        if(tag.equals("b")){
            synchronized (lock2) {
                try {
                    System.out.println("當前線程 : "  + Thread.currentThread().getName() + " 進入lock2執行");
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (lock1) {
                    System.out.println("當前線程 : "  + Thread.currentThread().getName() + " 進入lock1執行");
                }
            }
        }
    }
    
    public static void main(String[] args) {
        
        DeadLock d1 = new DeadLock();
        d1.setTag("a");
        DeadLock d2 = new DeadLock();
        d2.setTag("b");
         
        Thread t1 = new Thread(d1, "t1");
        Thread t2 = new Thread(d2, "t2");
         
        t1.start();
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        t2.start();
    }   
}