jstack应用-查找CPU飚高的原因
场景
在系统上线后，经常会遇到运维的同学跑过来说：“这次发版后，cpu线程使用率到一场，到100%了”。这时候不要慌，可以使用堆转储来分析到底是哪个线程引起的。
查找元凶
[root@java_mofei_01 test]# topMem: 16333644k total, 9472968k used, 6860676k free, 165616k buffersSwap: 0k total, 0k used, 0k free, 6665292k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 17850 root 20 0 7588m 112m 11m S 100.7 0.7 47:53.80 java 1552 root 20 0 121m 13m 8524 S 0.7 0.1 14:37.75 AliYunDun 3581 root 20 0 9750m 2.0g 13m S 0.7 12.9 298:30.20 java 1 root 20 0 19360 1612 1308 S 0.0 0.0 0:00.81 init 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd 3 root RT 0 0 0 0 S 0.0 0.0 0:00.14 migration/0
发现pid=17850的进程线程使用率100%，查询进程中哪个线程导致的问题
[root@java_mofei_01 test]# top -H -p 17850top - 17:43:15 up 5 days, 7:31, 1 user, load average: 0.99, 0.97, 0.91Tasks: 32 total, 1 running, 31 sleeping, 0 stopped, 0 zombieCpu(s): 3.7%us, 8.9%sy, 0.0%ni, 87.4%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%stMem: 16333644k total, 9592504k used, 6741140k free, 165700k buffersSwap: 0k total, 0k used, 0k free, 6781620k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 17880 root 20 0 7588m 112m 11m R 99.9 0.7 50:47.43 java 17856 root 20 0 7588m 112m 11m S 0.3 0.7 0:02.08 java 17850 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17851 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.23 java 17852 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.09 java 17853 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.12 java 17854 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.07 java 17855 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.06 java 17857 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.07 java 17858 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.08 java 17859 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.04 java 17860 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.05 java 17861 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17862 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17863 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17864 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.10 java 17865 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.12 java 17866 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.09 java 17867 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.12 java 17868 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17869 root 20 0 7588m 112m 11m S 0.0 0.7 0:01.04 java 17870 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17871 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17872 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17873 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17874 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17875 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17876 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17877 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17878 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17879 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java 17946 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java
发现17880的线程导致cpu飚高。
通过jstack查看线程信息
[root@java_mofei_01 test]# printf "%x\n" 17880 45d8[root@java_mofei_01 test]# jstack 17850|grep 45d8 -A 30"pool-1-thread-11" #20 prio=5 os_prio=0 tid=0x00007fc860352800 nid=0x45d8 runnable [0x00007fc8417d2000] java.lang.Thread.State: RUNNABLE at java.io.FileOutputStream.writeBytes(Native Method) at java.io.FileOutputStream.write(FileOutputStream.java:326) at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82) at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140) - locked <0x00000006c6c2e708> (a java.io.BufferedOutputStream) at java.io.PrintStream.write(PrintStream.java:482) - locked <0x00000006c6c10178> (a java.io.PrintStream) at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221) at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291) at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:104) - locked <0x00000006c6c26620> (a java.io.OutputStreamWriter) at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:185) at java.io.PrintStream.write(PrintStream.java:527) - eliminated <0x00000006c6c10178> (a java.io.PrintStream) at java.io.PrintStream.print(PrintStream.java:597) at java.io.PrintStream.println(PrintStream.java:736) - locked <0x00000006c6c10178> (a java.io.PrintStream) at com.demo.guava.HardTask.call(HardTask.java:18) at com.demo.guava.HardTask.call(HardTask.java:9) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745)"pool-1-thread-10" #19 prio=5 os_prio=0 tid=0x00007fc860345000 nid=0x45d7 waiting on condition [0x00007fc8418d3000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x00000006c6c14178> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
首先把pid 17880转成16进制
查询堆信息
发现HardTask（源码在末尾）第18行可能有问题
源码
public class HardTask implements Callable{ @Override public String call() throws Exception { while(true){ int a=100; int b=100; int rs=a+b/100-b; System.out.println(rs); } }}public class SimpleTask implements Callable { @Override public String call() throws Exception { Thread.sleep(300); //什么都不做 return null; }}public class CpuTest { public static void main(String[] args){ ExecutorService executorService=Executors.newFixedThreadPool(11); for (int i = 0; i < 10; i++) { executorService.submit(new SimpleTask()); } executorService.submit(new HardTask()); }}
源码很简单，就是创建了2种线程HardTask和SimpleTask。然后通过CpuTest进行启动。