模拟问题代码

构造一个死循环,造成CPU使用率100%。

> vim InfiniteLoop.java
public class InfiniteLoop {

    public static void main(String[] args) {
        Runnable target;
        Thread thread=new Thread(new Runnable() {
            @Override
            public void run() {
                long i=0;
                while (true){
                    i++;
                }
            }
        });
        thread.setName("rumenz");
        thread.start();
    }
}

> javac InfiniteLoop.java

运行问题代码

> java InfiniteLoop

发现系统CPU 100%

> top

6076 root      20   0 7096732  18972  10648 S 100.0  0.1   7:42.51 java InfiniteLoop

得到进程号是6076

根据top命令，发现PID为6076的Java进程占用CPU高达100%，出现故障。

找出具体的线程号

> top -Hp 6076

6096 root      20   0 7096732  18972  10648 R 99.7  0.1   9:09.92 java 

得到线程号是6096

将线程号转换成16进制

> printf "%x\n" 6096
17d0

万事具备,开始使用jstack打印堆栈信息

> jstack 6076 | grep 17d0 -A 30

"rumenz" #10 prio=5 os_prio=0 tid=0x00007fe0580f9000 nid=0x17d0 runnable [0x00007fe04431d000]
   java.lang.Thread.State: RUNNABLE
        at InfiniteLoop$1.run(InfiniteLoop.java:11)
        at java.lang.Thread.run(Thread.java:748)

"Service Thread" #9 daemon prio=9 os_prio=0 tid=0x00007fe0580e5800 nid=0x17ce runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread3" #8 daemon prio=9 os_prio=0 tid=0x00007fe0580c8000 nid=0x17cd waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread2" #7 daemon prio=9 os_prio=0 tid=0x00007fe0580c6000 nid=0x17cc waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007fe0580c4000 nid=0x17cb waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007fe0580c1000 nid=0x17ca waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007fe0580bf800 nid=0x17c9 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007fe05808e800 nid=0x17c8 in Object.wait() [0x00007fe044b25000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000000076d408ed8> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
        - locked <0x000000076d408ed8> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

at InfiniteLoop$1.run(InfiniteLoop.java:11),提示出代码11行, 查看源码发现有一个死循环。

总结解决JAVA,CPU 100%的问题

• top 查找CPU 100%的进程号pid
• top -Hp pid找出进程pid下最占CPU的线程号tid
• printf "%x\n" tid 将tid转换成十六进制 16tid
• jstack pid | grep 16tid -A 30打印堆栈信息
• 处理问题代码

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