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。