一、问题描述

Linux服务器的配置是4核16G，将war包部署到tomcat后，启动tomcat，发现内存占用率不高，但是CPU一直高达100%；浏览器输入相关url也无法访问该项目，且tomcat的进程一直存在，程序的配置什么的都没问题啊，一头雾水......通过top命令查看服务器的性能状况如下：

[root@aws-java-MAM ec2-user]# top

top - 18:49:21 up 45 min, 2 users, load average: 0.97, 0.50, 0.19

Tasks: 129 total, 1 running, 128 sleeping, 0 stopped, 0 zombie

Cpu0 : 95.1%us, 0.0%sy, 0.0%ni, 4.9%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

Cpu1 : 5.9%us, 0.0%sy, 0.0%ni, 94.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

Cpu2 : 1.6%us, 0.5%sy, 0.0%ni, 97.8%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

Cpu3 : 1.1%us, 0.0%sy, 0.0%ni, 98.9%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

Mem: 16330912k total, 2374776k used, 13956136k free, 20172k buffers

Swap: 0k total, 0k used, 0k free, 370244k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND

2141 root 20 0 7684m 1.7g 22m S 103.0 11.0 3:35.95 java

1423 root 20 0 449m 23m 2884 S 0.0 0.1 0:01.05 salt-minion

1959 root 20 0 98280 3860 2920 S 0.0 0.0 0:00.00 sshd

2278 root 20 0 98280 3836 2900 S 0.0 0.0 0:00.00 sshd

1387 postfix 20 0 81536 3436 2544 S 0.0 0.0 0:00.00 qmgr

1379 root 20 0 81284 3424 2520 S 0.0 0.0 0:00.01 master

1386 postfix 20 0 81364 3380 2508 S 0.0 0.0 0:00.00 pickup

1303 ntp 20 0 30720 2124 1508 S 0.0 0.0 0:00.00 ntpd

1986 root 20 0 105m 2000 1544 S 0.0 0.0 0:00.03 bash

1413 zabbix 20 0 42448 1972 1300 S 0.0 0.0 0:00.13 zabbix_agentd

可以看出PID为2141的java进程耗费内存11%，不算高，但是CPU达到103%，应该是哪里出现了死循环或者线程阻塞住了，导致CPU占用居高不下(各种配置个人觉得应该是没问题的)，怎么定位到具体线程或者程序位置呢？想到了jstack工具。

二、jstack简介

jstack是java虚拟机自带的一种堆栈跟踪工具。用于打印出给定的java进程ID或core file或远程调试服务的Java堆栈信息，使用jstack命令工具可以得到线程堆栈信息，根据这些线程堆栈信息，我们可以去检查Java程序出现的问题，如检测死锁，并输出死锁的信息的排查。

三、排查方式

1、首先通过如下命令显示线程列表

ps -mp pid -o THREAD,tid,time

[root@aws-java-MAM ec2-user]# ps -mp 2141 -o THREAD,tid,time |sort -rn

USER %CPU PRI SCNT WCHAN USER SYSTEM TID TIME

root 94.3 - - - - - - 00:04:04

root 85.9 19 - - - - 2185 00:03:21

root 3.7 19 - futex_ - - 2153 00:00:09

root 3.6 19 - futex_ - - 2152 00:00:09

root 2.8 19 - futex_ - - 2162 00:00:07

root 1.3 19 - futex_ - - 2154 00:00:03

root 0.9 19 - futex_ - - 2176 00:00:02

root 0.7 19 - futex_ - - 2147 00:00:02

root 0.7 19 - futex_ - - 2146 00:00:02

root 0.7 19 - futex_ - - 2145 00:00:02

root 0.7 19 - futex_ - - 2144 00:00:02

root 0.2 19 - futex_ - - 2148 00:00:00

root 0.2 19 - futex_ - - 2143 00:00:00

root 0.1 19 - inet_s - - 2209 00:00:00

root 0.0 19 - poll_s - - 2181 00:00:00

root 0.0 19 - poll_s - - 2179 00:00:00

root 0.0 19 - futex_ - - 2188 00:00:00

root 0.0 19 - futex_ - - 2183 00:00:00

root 0.0 19 - futex_ - - 2182 00:00:00

root 0.0 19 - futex_ - - 2180 00:00:00

root 0.0 19 - futex_ - - 2178 00:00:00

root 0.0 19 - futex_ - - 2175 00:00:00

从这里可以看出最耗CPU的线程ID是2185，占用CPU85.9%，TIME对应的是时间，持续了3分21秒钟了，命令中的sort -rn是倒序排序的意思。

2、将需要的线程ID转换为16进制格式

printf "%x\n" tid

[root@aws-java-MAM ec2-user]# printf "%x\n" 2185

889

3、打印线程的堆栈信息

jstack pid |grep tid -A 100

[root@aws-java-MAM ec2-user]# jstack 2141 |grep 889 -A 100

"Common.timer" #39 daemon prio=5 os_prio=0 tid=0x00007ffbc4398800 nid=0x889 runnable [0x00007ffc49b19000]

java.lang.Thread.State: RUNNABLE

at com.skymusic.service.cache.Cache$1.run(Cache.java:59)

at java.util.TimerThread.mainLoop(Timer.java:555)

at java.util.TimerThread.run(Timer.java:505)

"Timer-1" #37 daemon prio=5 os_prio=0 tid=0x00007ffbc4373800 nid=0x887 in Object.wait() [0x00007ffc49c1a000]

java.lang.Thread.State: TIMED_WAITING (on object monitor)

at java.lang.Object.wait(Native Method)

at java.util.TimerThread.mainLoop(Timer.java:552)

- locked <0x00000006c8201a40> (a java.util.TaskQueue)

at java.util.TimerThread.run(Timer.java:505)

"pool-4-thread-2" #36 prio=5 os_prio=0 tid=0x00007ffbc41f9800 nid=0x886 waiting on condition [0x00007ffc49f1b000]

java.lang.Thread.State: TIMED_WAITING (parking)

at sun.misc.Unsafe.park(Native Method)

- parking to wait for <0x00000006cb893460> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)

at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)

at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)

at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)

at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)

at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

at java.lang.Thread.run(Thread.java:745)

"AMQP Connection 172.31.44.144:5672" #35 prio=5 os_prio=0 tid=0x00007ffbc41f8000 nid=0x885 runnable [0x00007ffc4a01c000]

java.lang.Thread.State: RUNNABLE

at java.net.SocketInputStream.socketRead0(Native Method)

at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)

at java.net.SocketInputStream.read(SocketInputStream.java:170)

at java.net.SocketInputStream.read(SocketInputStream.java:141)

at java.io.BufferedInputStream.fill(BufferedInputStream.java:246)

at java.io.BufferedInputStream.read(BufferedInputStream.java:265)

- locked <0x00000006cb893a28> (a java.io.BufferedInputStream)

at java.io.DataInputStream.readUnsignedByte(DataInputStream.java:288)

at com.rabbitmq.client.impl.Frame.readFrom(Frame.java:91)

at com.rabbitmq.client.impl.SocketFrameHandler.readFrame(SocketFrameHandler.java:164)

- locked <0x00000006cb893a08> (a java.io.DataInputStream)

at com.rabbitmq.client.impl.AMQConnection$MainLoop.run(AMQConnection.java:596)

at java.lang.Thread.run(Thread.java:745)

"pool-2-thread-2" #34 prio=5 os_prio=0 tid=0x00007ffbc41f6800 nid=0x884 waiting on condition [0x00007ffc4a11d000]

java.lang.Thread.State: TIMED_WAITING (parking)

at sun.misc.Unsafe.park(Native Method)

- parking to wait for <0x00000006cbca2378> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)

at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)

at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)

at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)

at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)

at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

at java.lang.Thread.run(Thread.java:745)

"AMQP Connection 172.31.41.147:5672" #33 prio=5 os_prio=0 tid=0x00007ffbc41ef000 nid=0x883 runnable [0x00007ffc4a21e000]

java.lang.Thread.State: RUNNABLE

at java.net.SocketInputStream.socketRead0(Native Method)

at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)

at java.net.SocketInputStream.read(SocketInputStream.java:170)

at java.net.SocketInputStream.read(SocketInputStream.java:141)

at java.io.BufferedInputStream.fill(BufferedInputStream.java:246)

at java.io.BufferedInputStream.read(BufferedInputStream.java:265)

- locked <0x00000006cbcb8b60> (a java.io.BufferedInputStream)

at java.io.DataInputStream.readUnsignedByte(DataInputStream.java:288)

at com.rabbitmq.client.impl.Frame.readFrom(Frame.java:91)

at com.rabbitmq.client.impl.SocketFrameHandler.readFrame(SocketFrameHandler.java:164)

- locked <0x00000006cbcb8b40> (a java.io.DataInputStream)

at com.rabbitmq.client.impl.AMQConnection$MainLoop.run(AMQConnection.java:596)

at java.lang.Thread.run(Thread.java:745)

"Timer-0" #32 daemon prio=5 os_prio=0 tid=0x00007ffbf8f94800 nid=0x882 in Object.wait() [0x00007ffc4aad1000]

java.lang.Thread.State: TIMED_WAITING (on object monitor)

at java.lang.Object.wait(Native Method)

- waiting on <0x00000006cbcc2d48> (a java.util.TaskQueue)

at java.util.TimerThread.mainLoop(Timer.java:552)

- locked <0x00000006cbcc2d48> (a java.util.TaskQueue)

at java.util.TimerThread.run(Timer.java:505)

"Thread-7" #30 daemon prio=5 os_prio=0 tid=0x00007ffbf8f90800 nid=0x880 waiting on condition [0x00007ffc4b0f3000]

java.lang.Thread.State: WAITING (parking)

at sun.misc.Unsafe.park(Native Method)

- parking to wait for <0x00000006c8160e18> (a java.util.concurrent.CountDownLatch$Sync)

at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)

at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)

at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:997)

at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1304)

at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:231)

at com.dj.boot.Boot.init(Boot.java:108)

at com.dj.boot.Boot.dev(Boot.java:35)

at com.dj.filter.MD5Filter$1.run(MD5Filter.java:65)

at java.lang.Thread.run(Thread.java:745)

"startQuertz_QuartzSchedulerThread" #29 prio=5 os_prio=0 tid=0x00007ffbf8f77800 nid=0x87f in Object.wait() [0x00007ffc4b1f4000]

java.lang.Thread.State: TIMED_WAITING (on object monitor)

at java.lang.Object.wait(Native Method)

at org.quartz.core.QuartzSchedulerThread.run(QuartzSchedulerThread.java:410)

- locked <0x00000006c7dbf6b0> (a java.lang.Object)

"startQuertz_Worker-10" #28 prio=5 os_prio=0 tid=0x00007ffbf8f6c000 nid=0x87e in Object.wait() [0x00007ffc4b2f5000]

java.lang.Thread.State: TIMED_WAITING (on object monitor)

[root@aws-java-MAM ec2-user]#

-A后面的参数是行数，显示多少行堆栈信息，100就是显示100行。其中以下部分的内容引起了我的关注：

"Thread-7" #30 daemon prio=5 os_prio=0 tid=0x00007ffbf8f90800 nid=0x880 waiting on condition [0x00007ffc4b0f3000]

java.lang.Thread.State: WAITING (parking)

at sun.misc.Unsafe.park(Native Method)

- parking to wait for <0x00000006c8160e18> (a java.util.concurrent.CountDownLatch$Sync)

at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)

at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)

at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:997)

at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1304)

at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:231)

at com.dj.boot.Boot.init(Boot.java:108)

at com.dj.boot.Boot.dev(Boot.java:35)

at com.dj.filter.MD5Filter$1.run(MD5Filter.java:65)

at java.lang.Thread.run(Thread.java:745)

这里有个MD5Filter类的run方法，起了一个线程去初始化一个Boot配置(其他同事新增的业务，不了解)，然后一直在这里WATTING了，于是找了相关同事看了一下，发现新增的业务逻辑有问题，同事改了之后CPU就下来了。

4、再总结下排查CPU故障的方法和技巧

1)top命令

查看实时的CPU使用情况，也可以查看最近一段时间的CPU使用情况。

2)PS命令

进程状态监控命令；可以查看进程以及进程中线程的当前CPU使用情况，属于当前状态的采样数据。

3)jstack

查看某个进程的当前线程栈运行情况。根据这个命令的输出可以定位某个进程的所有线程的当前运行状态、运行代码，以及是否死锁等。

4)pstack

查看某个进程的当前线程栈运行情况。