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Java JVM-虚拟机专栏系列笔记，系统性学习可访问个人复盘笔记-技术博客 Java JVM-虚拟机 (opens new window)

• 排查过程
• 扩展
• 说明

排查过程

• 执行 top 命令，定位高 CPU 占用的 PID

  PID USER  PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+     COMMAND
10834 hdfs  20   0 6125996   3.4g   6800 S  107.0  5.4    343:35.01  /usr/java/jdk1.8...

• 执行 ps -mp PID -o THREAD,tid,time 命令查看线程耗时情况

ps -mp 10834 -o THREAD,tid,time
USER     %CPU PRI SCNT WCHAN  USER SYSTEM   TID     TIME
hdfs      0.2   -    - -         -      -     - 05:43:35
hdfs      0.0  19    - futex_    -      - 11013 00:47:47 --以该线程长耗时为例分析
hdfs      0.0  19    - futex_    -      - 11014 00:01:21
hdfs      0.0  19    - futex_    -      - 11035 00:00:07
hdfs      0.0  19    - futex_    -      - 11037 00:20:04
hdfs      0.0  19    - ep_pol    -      - 11401 00:04:52
hdfs      0.0  19    - ep_pol    -      - 11402 00:04:31
hdfs      0.0  19    - futex_    -      - 11403 00:21:01

• 执行 printf "%x\n" TID 将 tid 转换为十六进制

printf "%x\n" 11013
2b05

• 执行 jstack PID |grep TID -A 30 定位具体线程

jstack 10834 |grep 2b05 -A 30
"C1 CompilerThread0" #7 daemon prio=9 os_prio=31 cpu=398.45ms elapsed=1607.13s tid=0x00007fd03c809800 nid=0x3d03 waiting on condition  [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE
   No compile task
--
"生产者-3" #14 prio=5 os_prio=31 cpu=375.00ms elapsed=1606.74s tid=0x00007fd03b8bd800 nid=0x6403 waiting on condition  [0x0000700009200000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
	at java.lang.Thread.sleep(java.base@11.0.2/Native Method)
	at io.gourd.java.concurrency.app.pc.CarFactory$Producer.run(CarFactory.java:45)
	at java.lang.Thread.run(java.base@11.0.2/Thread.java:834)

"生产者-4" #15 prio=5 os_prio=31 cpu=375.46ms elapsed=1606.74s tid=0x00007fd03b931000 nid=0xa203 waiting on condition  [0x0000700009303000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
	at java.lang.Thread.sleep(java.base@11.0.2/Native Method)
	at io.gourd.java.concurrency.app.pc.CarFactory$Producer.run(CarFactory.java:45)
	at java.lang.Thread.run(java.base@11.0.2/Thread.java:834)

扩展

根据实际线程情况定位相关代码，如果定位到 GC 相关线程引起高 CPU 问题，可使用 jstat (opens new window) 相关命令观察 GC 情况
例如： jstat -gcutil -t -h 5 PID 500 10

说明

实际生产过程中我们可以选择更多的工具进行运行监控、分析 dump 文件：

• 推荐-Memory Analyzer (MAT) (opens new window)
• 推荐-付费-jprofiler (opens new window)
• 推荐-Flight Recorder-飞行记录仪 (opens new window)
• jhsdb (opens new window)
• jconsole (opens new window)
• Java Mission Control (opens new window)

更多 JDK 相关命令详细用法可参考 Java JVM JDK13 诊断命令处理工具 jps,jstat,jinfo,jmap,jstack,jcmd (opens new window)

更多故障诊断及调优，参考本专栏 Java JVM（JDK13）-专栏文章目录汇总 (opens new window)。