死锁编码及定位分析

是什么

​ 死锁是指两个或两个以上的进程在执行过程中,因争夺资源而造成的一种互相等待的现象,若无外力干涉,他们都将无法进行下去,如果系统资源充足,进行的资源请求都能够得到满足,死锁出现的可能性就很低,否则就回因争夺有限的资源而陷入死锁.

package top.ygy.thread;

public class DeadLockDemo {
	public static void main(String[] args) {
		String lockA = "lockA";
		String lockB = "lockB";
		
		new Thread(new HoldLockTHread(lockA,lockB),"ThreadAAA").start();
		new Thread(new HoldLockTHread(lockB,lockA),"ThreadBBB").start();
	}
}

class HoldLockTHread implements Runnable {

	private String lockA;
	private String lockB;

	public HoldLockTHread(String lockA, String lockB) {
		this.lockA = lockA;
		this.lockB = lockB;
	}

	@Override
	public void run() {
		synchronized (lockA) {
			System.out.println(Thread.currentThread().getName() + "\t 自己持有:"
					+ lockA + ",尝试获得:" + lockB);
			synchronized (lockB) {
				System.out.println(Thread.currentThread().getName() + "\t 自己持有:"
						+ lockB + ",尝试获得:" + lockA);
			}
		}
	}

}

产生原因

1. 系统资源不足
2. 进程运行推进的顺序不合适
3. 资源分配不当

解决

工具

• jps 命令类似与 linux 的 ps 命令，但是它只列出系统中所有的 Java 应用程序。
• jstack是java虚拟机自带的一种堆栈跟踪工具

查看进程?

• linux ps -ef | grep xxxx ls -f
• windows下的java运行程序,也有类似查看进程的命令,但是我们目前查看的只是java
  • jsp -l
• jsp查出端口号,用jstack查看具体信息
  • jstack 端口号

C:\Users\Administrator>jps -l
55408 sun.tools.jps.Jps
56256 top.ygy.thread.DeadLockDemo
46376

C:\Users\Administrator>jstack 56256

Found one Java-level deadlock:
=============================
"ThreadBBB":
  waiting to lock monitor 0x0000000057086768 (object 0x00000000d60ca108, a java.
lang.String),
  which is held by "ThreadAAA"
"ThreadAAA":
  waiting to lock monitor 0x0000000057089208 (object 0x00000000d60ca140, a java.
lang.String),
  which is held by "ThreadBBB"

Java stack information for the threads listed above:
===================================================
"ThreadBBB":
        at top.ygy.thread.HoldLockTHread.run(DeadLockDemo.java:29)
        - waiting to lock <0x00000000d60ca108> (a java.lang.String)
        - locked <0x00000000d60ca140> (a java.lang.String)
        at java.lang.Thread.run(Thread.java:748)
"ThreadAAA":
        at top.ygy.thread.HoldLockTHread.run(DeadLockDemo.java:29)
        - waiting to lock <0x00000000d60ca140> (a java.lang.String)
        - locked <0x00000000d60ca108> (a java.lang.String)
        at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.