一、命令行工具jstack

用于查看线程状态

  • 例子

    1. public class ThreadState {
    3.   public static void main(String[] args) {
    4.       new Thread(new TimeWaiting(), "TimeWaitingThread").start();
    5.       new Thread(new Waiting(), "WaitingThread").start();
    6.       // 使用两个Blocked线程，一个获取锁成功，另一个被阻塞
    7.       new Thread(new Blocked(), "BlockedThread-1").start();
    8.       new Thread(new Blocked(), "BlockedThread-2").start();
    9.   }
    11.   // 该线程不断地进行睡眠
    12.   static class TimeWaiting implements Runnable {
    13.       @Override
    14.       public void run() {
    15.           while (true) {
    16.               try {
    17.                   TimeUnit.SECONDS.sleep(100);
    18.               } catch (InterruptedException e) {
    19.                   e.printStackTrace();
    20.               }
    21.           }
    22.       }
    23.   }
    25.   // 该线程在Waiting.class实例上等待
    26.   static class Waiting implements Runnable {
    27.       @Override
    28.       public void run() {
    29.           while (true) {
    30.               synchronized (Waiting.class) {
    31.                   try {
    32.                       Waiting.class.wait();
    33.                   } catch (InterruptedException e) {
    34.                       e.printStackTrace();
    35.                   }
    36.               }
    37.           }
    38.       }
    39.   }
    41.   // 该线程在Blocked.class实例上加锁后，不会释放该锁
    42.   static class Blocked implements Runnable {
    43.       public void run() {
    44.           synchronized (Blocked.class) {
    45.               while (true) {
    46.                   try {
    47.                       TimeUnit.SECONDS.sleep(100);
    48.                   } catch (InterruptedException e) {
    49.                       e.printStackTrace();
    50.                   }
    51.               }
    52.           }
    53.       }
    54.   }
    55. }

  • 启动以上程序后，控制台上输入jps 查看进程

    1. $ jps
    2. 7012 Main
    3. 32037 Jps
    4. 26870 Main
    5. 31862 Launcher
    6. 31863 ThreadState
    7. 29629 KotlinCompileDaemon

  • 查看 ThreadState 的状态 : jstack　进程id

  1. jstack　31863
  1. //...省略
  3. //BlockedThread-2 阻塞状态: BLOCKED
  4. "BlockedThread-2" #13 prio=5 os_prio=0 tid=0x00007f0dd8214800 nid=0x7c98 waiting for monitor entry [0x00007f0dc1600000]
  5.    java.lang.Thread.State: BLOCKED (on object monitor)
  6.    at concurrency.ThreadState$Blocked.run(ThreadState.java:54)
  7.    - waiting to lock <0x00000000d93089b0> (a java.lang.Class for concurrency.ThreadState$Blocked)
  8.    at java.lang.Thread.run(Thread.java:748)
  10. // BlockedThread-1  获取了锁，执行sleep()方法，进入超时等待状态: TIMED_WAITING
  11. "BlockedThread-1" #12 prio=5 os_prio=0 tid=0x00007f0dd8213000 nid=0x7c97 waiting on condition [0x00007f0dc1701000]
  12.    java.lang.Thread.State: TIMED_WAITING (sleeping)
  13.    at java.lang.Thread.sleep(Native Method)
  14.    at concurrency.ThreadState$Blocked.run(ThreadState.java:54)
  15.    - locked <0x00000000d93089b0> (a java.lang.Class for concurrency.ThreadState$Blocked)
  16.    at java.lang.Thread.run(Thread.java:748)
  17. //WaitingThread　等待状态: WAITING
  18. "WaitingThread" #11 prio=5 os_prio=0 tid=0x00007f0dd8211000 nid=0x7c96 in Object.wait() [0x00007f0dc1802000]
  19.    java.lang.Thread.State: WAITING (on object monitor)
  20.    at java.lang.Object.wait(Native Method)
  21.    - waiting on <0x00000000d9308dc8> (a java.lang.Class for concurrency.ThreadState$Waiting)
  22.    at java.lang.Object.wait(Object.java:502)
  23.    at concurrency.ThreadState$Waiting.run(ThreadState.java:39)
  24.    - locked <0x00000000d9308dc8> (a java.lang.Class for concurrency.ThreadState$Waiting)
  25.    at java.lang.Thread.run(Thread.java:748)
  26. // TimeWaitingThread　超时等待状态:TIMED_WAITING
  27. "TimeWaitingThread" #10 prio=5 os_prio=0 tid=0x00007f0dd8210000 nid=0x7c95 waiting on condition [0x00007f0dc1903000]
  28.    java.lang.Thread.State: TIMED_WAITING (sleeping)
  29.    at java.lang.Thread.sleep(Native Method)
  30.    at concurrency.ThreadState$TimeWaiting.run(ThreadState.java:24)
  31.    at java.lang.Thread.run(Thread.java:748)
  33. //省略...

二、vmstat 查看线程切换次数

参考
https://wiki.openjdk.java.net/display/CodeTools