为什么一个空闲的Java线程显示出高CPU使用率？

Question

[jboss@prodmachine ~]$ ps -elf | grep java
0 S jboss     8844     1  0  80   0 - 28275 wait   15:30 ?        00:00:00 /bin/sh /usr/java/wildfly/bin/standalone.sh -c standalone.xml
0 S jboss     8896  8844 99  80   0 - 7337773 futex_ 15:30 ?      08:16:14 /usr/java/default/bin/java -D[Standalone] -server -Xms64m -Xmx25600m -XX:MetaspaceSize=96M -XX:MaxMetaspaceSize=1024m -Djava.net.preferIPv4Stack=true -Djboss.modules.system.pkgs=org.jboss.byteman,com.newrelic -Djava.awt.headless=true -javaagent:/usr/java/wildfly/newrelic/newrelic.jar -Dorg.jboss.boot.log.file=/usr/java/wildfly/standalone/log/server.log -Dlogging.configuration=file:/usr/java/wildfly/standalone/configuration/logging.properties -jar /usr/java/wildfly/jboss-modules.jar -mp /usr/java/wildfly/modules org.jboss.as.standalone -Djboss.home.dir=/usr/java/wildfly -Djboss.server.base.dir=/usr/java/wildfly/standalone -c standalone.xml

top -n 1 -H -p 8896

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                           
 9310 jboss     20   0 28.0g 4.4g  33m S 43.3 15.2   3:16.72 java                                                                               
 9207 jboss     20   0 28.0g 4.4g  33m S 13.8 15.2  42:00.05 java                                                                               
 9292 jboss     20   0 28.0g 4.4g  33m S 13.8 15.2   3:17.87 java

[jboss@prodmachine ~]$ /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-8.b13.39.39.amzn1.x86_64/bin/jstack -l 8896 > /tmp/jstack.txt

揭示了这一点

"default task-86" #272 prio=5 os_prio=0 tid=0x00000000090ee800 nid=0x245e waiting on condition [0x00007f3220cee000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x0000000181c9e050> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
        at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

但我读到的所有内容都表明，处于“等待”状态的线程不应该占用CPU资源。为什么我会看到这个奇怪的结果？我是不是一路上搞砸了什么？

Answer 1

与其使用命令行来监视线程活动，不如使用Java visual VM，这会更好，而且对您有极大的帮助。

处于“等待”或“Hibernate”状态的线程是否使用CPU？

进入和退出睡眠/等待状态需要时间。这是成本相对较小，但非微不足道，如果调用足够。