java调试-jstack命令

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jstack命令使用

jstack可用于导出java运用程序的线程堆栈，其基本使用语法为：

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jstack [-l] pid

-l 打印关于锁的附加信息,例如属于java.util.concurrent的ownable synchronizers列表.

常用用法

下面这段代码运行之后会出现死锁现象(因为线程1持有lock1，在等待lock2，线程2持有lock2在等待lock1，造成了循环等待，形成死锁)：

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package com.zsr.test.lock;
/**
 * 
 * Created by david.zhang
 */
public class TestDeadLock {
    private static final Object lock1 = new Object();
    private static final Object lock2 = new Object();
    public static void main(String[] args) {
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (lock1) {
                    try {
                        Thread.sleep(1000);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    synchronized (lock2) {
                        System.out.println("线程1执行....");
                    }
                }
            }
        });
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (lock2) {
                    try {
                        Thread.sleep(1000);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    synchronized (lock1) {
                        System.out.println("线程2执行...");
                    }
                }
            }
        });
        t1.start();
        t2.start();
    }
}

运行这段代码，然后使用jstack命令导出这个程序的线程堆栈信息：

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nalideMacBook-Pro-4:public nali$ jstack -l 35072 > /Users/nali/deadlock.txt

打开导出的线程堆栈信息文件，文件末尾如下所示：

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Found one Java-level deadlock:
=============================
"Thread-1":
  waiting to lock monitor 0x00007fe6d48432b8 (object 0x00000007d558e9d8, a java.lang.Object),
  which is held by "Thread-0"
"Thread-0":
  waiting to lock monitor 0x00007fe6d4844758 (object 0x00000007d558e9e8, a java.lang.Object),
  which is held by "Thread-1"
Java stack information for the threads listed above:
===================================================
"Thread-1":
	at com.zsr.test.lock.TestDeadLock$2.run(TestDeadLock.java:39)
	- waiting to lock <0x00000007d558e9d8> (a java.lang.Object)
	- locked <0x00000007d558e9e8> (a java.lang.Object)
	at java.lang.Thread.run(Thread.java:745)
"Thread-0":
	at com.zsr.test.lock.TestDeadLock$1.run(TestDeadLock.java:23)
	- waiting to lock <0x00000007d558e9e8> (a java.lang.Object)
	- locked <0x00000007d558e9d8> (a java.lang.Object)
	at java.lang.Thread.run(Thread.java:745)
Found 1 deadlock.

导出的线程堆栈文件中明确提示发现死锁，并且指明了死锁的原因。

jstack不仅能够导出线程堆栈，还能自动进行死锁检测，输出线程死锁原因。

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