場景

在系統上線后，經常會遇到運維的同學跑過來說：“這次發版后，cpu線程使用率到一場，到100%了”。這時候不要慌，可以使用堆轉儲來分析到底是哪個線程引起的。

查找元兇

[root@java_mofei_01 test]# top Mem: 16333644k total, 9472968k used, 6860676k free, 165616k buffers Swap: 0k total, 0k used, 0k free, 6665292k cachedPID 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

發現pid=17850的進程線程使用率100%，查詢進程中哪個線程導致的問題

[root@java_mofei_01 test]# top -H -p 17850 top - 17:43:15 up 5 days, 7:31, 1 user, load average: 0.99, 0.97, 0.91 Tasks: 32 total, 1 running, 31 sleeping, 0 stopped, 0 zombie Cpu(s): 3.7%us, 8.9%sy, 0.0%ni, 87.4%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 16333644k total, 9592504k used, 6741140k free, 165700k buffers Swap: 0k total, 0k used, 0k free, 6781620k cachedPID 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

發現17880的線程導致cpu飚高。

通過jstack查看線程信息

[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: RUNNABLEat 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轉成16進制
• 查詢堆信息
• 發現HardTask（源碼在末尾）第18行可能有問題

  源碼

public class HardTask implements Callable<String> {@Overridepublic 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<String> {@Overridepublic 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());} }

源碼很簡單，就是創建了2種線程HardTask和SimpleTask。然后通過CpuTest進行啟動。

轉載于:https://blog.51cto.com/4436396/2118787

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