CPU 100%肯定是出现死锁，这个时候观察内存还是够用的，但是CPU一直100%，以下几步解决：
1. 找到进程消耗cpu最大的
$top
top - :: up days, :, user, load average: 0.75, 0.60, 0.53
Tasks: total, running, sleeping, stopped, zombie
Cpu(s): 11.6%us, 7.0%sy, 0.0%ni, 81.3%id, 0.0%wa, 0.0%hi, 0.0%si, 0.1%st
Mem: 8388608k total, 8381460k used, 7148k free, 0k buffers
Swap: 1999864k total, 0k used, 1999864k free, 4089340k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
admin - 5631m .0g 102m S : java
2. 打出进程中线程占用情况：
$top -p -H
top - :: up days, :, user, load average: 0.63, 0.59, 0.54
Tasks: total, running, sleeping, stopped, zombie
Cpu(s): 0.7%us, 0.3%sy, 0.0%ni, 98.8%id, 0.0%wa, 0.0%hi, 0.0%si, 0.2%st
Mem: 8388608k total, 8382160k used, 6448k free, 0k buffers
Swap: 1999864k total, 0k used, 1999864k free, 4089636k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
admin - 5631m .0g 102m S :21.02 java
admin - 5631m .0g 102m S :56.39 java
3. dump文件：
$ jstack > Desktop/jstack.log
4. 找到#2步的PID对应的16进制
$printf %x
269d6
5. 在#3的dump文件中找到#4对应的线程堆栈(0x269d6)：
zhangdeMacBook-Air:~ zhang$ more Desktop/jstack.log
2016-07-17 11:45:20
Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.79-b02 mixed mode):
"Attach Listener" daemon prio=5 tid=0x00007f9aab82a800 nid=0x580b waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"SocketConnectorIoProcessor-0.2" daemon prio=5 tid=0x00007f9aab43b800 nid=0x7003 runnable [0x00000001699a4000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.KQueueArrayWrapper.kevent0(Native Method)
at sun.nio.ch.KQueueArrayWrapper.poll(KQueueArrayWrapper.java:200)
at sun.nio.ch.KQueueSelectorImpl.doSelect(KQueueSelectorImpl.java:103)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:87)
- locked <0x00000001585a8078> (a sun.nio.ch.Util$2)
- locked <0x00000001585a8088> (a java.util.Collections$UnmodifiableSet)
- locked <0x00000001585a8028> (a sun.nio.ch.KQueueSelectorImpl)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:98)
at org.apache.mina.transport.socket.nio.SocketIoProcessor$Worker.run(SocketIoProcessor.java:480)
at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
6. 结合dump和代码分析问题原因，一般都能找到原因
Java ConcurrentModificationException异常原因和解决方法