Linux下java进程CPU占用率高分析方法

在工做当中，确定会遇到由代码所致使的高CPU耗用以及内存溢出的状况。这种状况发生时，咱们怎么去找出缘由并解决。

通常解决方法是经过top命令找出消耗资源高的线程id，利用strace命令查看该线程全部系统调用。

1. 经过top命令找到可疑进程PID

top - 09:37:18 up 70 days, 16:29,  2 users,  load average: 1.13, 1.04, 0.97
Tasks: 105 total,   1 running, 104 sleeping,   0 stopped,   0 zombie
Cpu(s):  1.0%us,  4.9%sy,  0.0%ni, 93.6%id,  0.0%wa,  0.0%hi,  0.0%si,  0.5%st
Mem:   2067816k total,  1756680k used,   311136k free,   236340k buffers
Swap:   524284k total,   255508k used,   268776k free,   277040k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
24138 apache    20   0 1273m 384m 3668 S 103.3 19.0   1232:39 java
 3359 root      39  19  2704   36    0 S  0.3  0.0   4:39.34 gam_server
 6696 root      20   0 34148 1604  244 S  0.3  0.1   5:06.63 httpd
19254 root      20   0  785m 221m 3176 S  0.3 11.0   9:04.36 java
    1 root      20   0  2224   28    0 S  0.0  0.0   1:22.46 init
    2 root      20   0     0    0    0 S  0.0  0.0   0:00.00 kthreadd
    3 root      20   0     0    0    0 S  0.0  0.0   0:33.42 ksoftirqd/0
    5 root      20   0     0    0    0 S  0.0  0.0   0:00.03 kworker/u:0

从上面命令中能够看出java进程CPU利用率一直保持100%，稳居不下，找到PID 24138

2. 找出消耗资源最高的线程

top -H -p  24138 能够不用第一步，直接执行命令 top -H ，就能够查看到消耗资源最高的线程

top - 09:49:49 up 70 days, 16:41,  2 users,  load average: 1.01, 1.04, 1.00
Tasks:  72 total,   1 running,  71 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.6%us,  1.3%sy,  0.0%ni, 97.7%id,  0.1%wa,  0.0%hi,  0.0%si,  0.2%st
Mem:   2067816k total,  1760840k used,   306976k free,   236744k buffers
Swap:   524284k total,   253344k used,   270940k free,   279092k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
24167 apache    20   0 1273m 384m 3688 R 99.1 19.0   1169:43 java
24152 apache    20   0 1273m 384m 3688 S  2.0 19.0   0:28.58 java
24188 apache    20   0 1273m 384m 3688 S  2.0 19.0   4:56.69 java
24138 apache    20   0 1273m 384m 3688 S  0.0 19.0   0:00.00 java

3. 查看这个线程全部系统调用

strace -p 24167

经过这3步基本能够找出什么缘由致使java进程占用那么高CPU资源。

咱们也能够获取堆栈信息：

jstack 28857 > a.txt

从打印出来的堆栈信息文件（a.txt）里，找到该进程（28871）信息：

Thread 28871: (state = IN_NATIVE)
 - sun.nio.ch.ServerSocketChannelImpl.accept0(java.io.FileDescriptor, java.io.FileDescriptor, java.net.InetSocketAddress[])@bci=0 (Compiled frame; information may be imprecise)
 - sun.nio.ch.ServerSocketChannelImpl.accept() @bci=130, line=226 (Compiled frame)
 - org.eclipse.jetty.server.nio.SelectChannelConnector.accept(int) @bci=20, line=97 (Compiled frame)
 - org.eclipse.jetty.server.AbstractConnector$Acceptor.run() @bci=153, line=833 (Compiled frame)
 - org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(java.lang.Runnable) @bci=1, line=598 (Interpreted frame)
 - org.eclipse.jetty.util.thread.QueuedThreadPool$3.run() @bci=47, line=533 (Interpreted frame)
 - java.lang.Thread.run() @bci=11, line=722 (Interpreted frame)