tomcat cpu占用过高，系统负载高问题跟踪

2011-09-06 线上8核 linux服务器，负载为8为正常情况，目前CPU负载过高，最高负载30多，平均负载在20左右，已经持续近一周，具体占用CPU资源的服务是tomcat_sc，占用CPU资源高达：720% 使用jconsole去跟踪更改catalina.sh 启动设置：

$ CATALINA_OPTS="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=8933 -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false -Djava.rmi.server.hostname=$server_ip";

import java.rmi.registry.LocateRegistry;
import javax.management.MBeanServer;
import javax.management.remote.JMXConnectorServer;
import javax.management.remote.JMXConnectorServerFactory;
import javax.management.remote.JMXServiceURL;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.net.MalformedURLException;

public class JmxTest {
public static void main(String[] args) {
MBeanServer mbeanServer =
ManagementFactory.getPlatformMBeanServer();

JMXServiceURL url = null;
try {
url = new JMXServiceURL(
"service:jmx:rmi://localhost:12199/jndi/rmi://localhost:8933/jmxrmi");
} catch (MalformedURLException e) {
e.printStackTrace();
}

JMXConnectorServer connectorServer =
null;
try {
connectorServer = JMXConnectorServerFactory.newJMXConnectorServer(url, null, mbeanServer);
} catch (IOException e) {
e.printStackTrace();
}

try {
System.setProperty("java.rmi.server.randomIDs", "true");
LocateRegistry.getRegistry(8933);
connectorServer.start();
} catch (IOException e) {
e.printStackTrace(); 
}

}
}

hostname -i 为127.0.0.1 测试服务器配置完后，在本机使用jconsole连接，输入测试服务器帐号密码即可连上。网上资料说要改hostname，没有更改hostname也可行线上先开了服务器端口，又开了本机端口，telnet可以连上，但jconsole无法连接，查google，说： the jvm you're trying to connect to actually exposes *two* ports, the one specified via -Dcom.sun.management.jmxremote.port, and some other one. The 2nd one is random, but jconsole wants to connect to it, so if you have a firewall, and you've only opened up the above port, you're hosed. 只开放了一个端口就不可以？必须外网服务器所有端口都对内网开放？继续跟踪。 jmap jconsole jstack都是java自带的jmx 问题跟踪工具，可以学习一下帮助分析定位内存溢出程序死锁之类的程序问题使用 jmap 查看内存状况 jmap -histo:live pid 服务自建类的数量并不多 jstack 跟踪堆栈也没看出个所以然继续jconsole调查 google “jconsole remote set random port to certain” 找到一篇像样的文章： http://www.componative.com/content/controller/developer/insights/jconsole3/ 于是写了servlet去注册指定端口未果在测试机上先试试写java文件：出现 java.rmi.AccessException: Cannot modify this registry 错误注释掉 catalina.sh的启动设置 -Dcom.sun.management.jmxremote.port=8933 也不行最终放弃了jconsole 使用 java.lang.management..ThreadMXBean 用焱哥转发新阳提供的 jsp页面分析性能问题，主要是看线程阻塞情况主要代码：

ThreadMXBean tm = ManagementFactory.getThreadMXBean();
tm.setThreadContentionMonitoringEnabled(true);
<%
long [] tid = tm.getAllThreadIds();
ThreadInfo [] tia = tm.getThreadInfo(tid, Integer.MAX_VALUE);

long [][] threadArray = new long[tia.length][2];

for (int i = 0; i < tia.length; i++) {
long threadId = tia[i].getThreadId();

long cpuTime = tm.getThreadCpuTime(tia[i].getThreadId())/(1000*1000*1000);
threadArray[i][0] = threadId;
threadArray[i][1] = cpuTime;
}

检测到如下线程问题: Thread ID: 89 Thread Name: http-6080-Processor73 Thread State: RUNNABLE Thread Lock Name: null Thread Lock Owner Name: null Thread CPU Time: 35678 sec Stack Info: (depth:31) +java.util.HashMap.get(HashMap.java:303) +com.netqin.baike.server.nqrs.CloudSecurityCommand.writePkgsLog(CloudSecurityCommand.java:466) +com.netqin.baike.server.nqrs.CloudSecurityCommand.execute(CloudSecurityCommand.java:153) +com.netqin.baike.server.BaikeServer.service(BaikeServer.java:64) +sun.reflect.GeneratedMethodAccessor33.invoke(Unknown Source) CPU占用时间达到 35678秒，到下午到了50000秒左右，tomcat的CPU占用达到了200% 分析代码，发现是单例bean中使用了 hashmap 作为类对象，多线程访问时类成员hashmap并不是线程安全的非单例，引起了问题。更正代码后，几个月没有发现问题