多线程六：死锁例子与排查

死锁产生情况：双方互相持有对方的锁的情况

死锁示例代码：

public class DealThread implements Runnable {
	public String username;
	public Object lock1 = new Object();
	public Object lock2 = new Object();
	public void setFlag(String username) {
		this.username = username;
	}
	
	@Override
	public void run() {
		if(username.equals("a")) {
			synchronized(lock1) {
				try {
					System.out.println("username = " + username);
					Thread.sleep(3000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				synchronized(lock2) {
					System.out.println("lock2执行");
				}
			}
		}
		if(username.equals("b")) {
			synchronized(lock2) {
				try {
					System.out.println("username = " + username);
					Thread.sleep(3000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				synchronized(lock1) {
					System.out.println("lock1执行");
				}
			}
		}
	}
}

Run方法：
public class Run {
	public static void main(String[] args) {
		try {
			DealThread t1 = new DealThread();
			t1.setFlag("a");
			Thread thread1 = new Thread(t1);
			thread1.start();
			Thread.sleep(100);
			t1.setFlag("b");
			Thread thread2 = new Thread(t1);
			thread2.start();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

运行结果：

排查：

使用jdk自带工具进行排查
执行jps指令，可以查看当前运行的线程：

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可以看到Run线程的id值为3684。在执行jstack命令，查看结果：