详细介绍：参考Thread内部类:State
WAITING与TIMED_WAITING: 调用以下三个方法会进入WAITING状态： * Object.wait() 不设置超时时间 * Thread.join() 不设置超时时间 * LockSupport.park() 不设置超时时间 调用下面的方法会进入TIMED_WAITING状态： * Object.wait(time) * Thread.join(time) * Thread.sleep(time) * LockSupport.parkNanos(time) * LockSupport.parkUntil(time)
jstack 是一个可以用来打印java进程中的线程堆栈信息的工具。一般都位于jdk安装目录的bin目录下。 一般，jstack都用来检测死锁，以及分析当前程序运行状态。
jstack [options] pid pid:即进程id，可以通过jps命令查看 options:可选选项。一般常用的是-l和-m，-l用于打印详细的堆栈信息，包括当前线程获得到的同步器(AbstractOwnableSynchronizer)。-m则会打印包含C++或C的堆栈信息。
例如： 命令：jstack 10968 则会把进程号为10968的进程所包含的线程信息打印出来。 其中的部分结果如下：
"main" #1 prio=5 os_prio=0 tid=0x00007fab88009800 nid=0x2add waiting on condition [0x00007fab8ee92000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:304) at test.DeadLockTest.main(DeadLockTest.java:17)命令：jstack -l 10968则会包含当前线程获取到的同步器。 其中的部分结果如下：
"main" #1 prio=5 os_prio=0 tid=0x00007fab88009800 nid=0x2add waiting on condition [0x00007fab8ee92000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:304) at test.DeadLockTest.main(DeadLockTest.java:17) Locked ownable synchronizers: - None可以看到，带-l参数的，在线程信息后面有个’ Locked ownable synchronizers:’信息。
关于jstack的使用，下面两篇文章写的很不错，非常建议一看: 1. java-thread-dumps 2. java-thread-dumps-2
我们来看一下，当线程处于不同状态的时候，通过jstack看到的是什么样子的。
WAITING状态通过上面的讲解我们知道，线程进入waiting状态可以通过三种方式：1.Object.wait,2.Thread.join,3.LockSupport.park ，那么我们分别来看下，当程序分别通过这三种方式进入WAITING状态的时候，对应的jstack信息是怎样的。
1.Object.wait方式 代码：
public class WaitingTest { public static void main(String[] args) throws InterruptedException { // Object.wait synchronized (WaitingTest.class) { WaitingTest.class.wait(); } }}jstack 结果(省略其他部分，下同):
"main" #1 prio=5 os_prio=0 tid=0x00007f384c009800 nid=0x2d9c in Object.wait() [0x00007f385268b000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d6ddb9a0> (a java.lang.Class for test.WaitingTest) at java.lang.Object.wait(Object.java:502) at test.WaitingTest.main(WaitingTest.java:8) - locked <0x00000000d6ddb9a0> (a java.lang.Class for test.WaitingTest)2.Thread.join方式 代码：
public static void main(String[] args) throws InterruptedException { // Thread.join Thread thread = new Thread() { @Override public void run() { System.out.println("run"); try { Thread.sleep(1000 * 300); } catch (InterruptedException e) { e.printStackTrace(); } } }; thread.start(); // 当前线程调用thread线程的join方法 thread.join(); // 只有thread的run方法执行完成之后，才会执行输出 System.out.println("Current thread running"); }jstack:
"main" #1 prio=5 os_prio=0 tid=0x00007f88cc009800 nid=0x2f10 in Object.wait() [0x00007f88d5b73000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d6ddddf8> (a test.WaitingTest$1) at java.lang.Thread.join(Thread.java:1245) - locked <0x00000000d6ddddf8> (a test.WaitingTest$1) at java.lang.Thread.join(Thread.java:1319) at test.WaitingTest.main(WaitingTest.java:23) Locked ownable synchronizers: - None3.LockSupport.park方式 代码：
public static void main(String[] args) throws InterruptedException { LockSupport.park(); }jstack:
"main" #1 prio=5 os_prio=0 tid=0x00007f6efc009800 nid=0x2f88 waiting on condition [0x00007f6f034dd000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:304) at test.WaitingTest.main(WaitingTest.java:8) Locked ownable synchronizers: - None TIMED_WAITING1.Object.wait(time) 代码：
public static void main(String[] args) throws InterruptedException { synchronized (WaitingTest.class) { WaitingTest.class.wait(1000 * 50); } }jstack:
"main" #1 prio=5 os_prio=0 tid=0x00007fd598009800 nid=0x301b in Object.wait() [0x00007fd59eea0000] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d6ddb9b8> (a java.lang.Class for test.WaitingTest) at test.WaitingTest.main(WaitingTest.java:9) - locked <0x00000000d6ddb9b8> (a java.lang.Class for test.WaitingTest) Locked ownable synchronizers: - None2.Thread.join(time) 代码:
public static void main(String[] args) throws InterruptedException { // Thread.join Thread thread = new Thread() { @Override public void run() { System.out.println("run"); try { Thread.sleep(1000 * 300); } catch (InterruptedException e) { e.printStackTrace(); } } }; thread.start(); // 当前线程调用thread线程的join方法 thread.join(1000 * 200); // 只有thread的run方法执行完成之后，才会执行输出 System.out.println("Current thread running"); }jstack:
"main" #1 prio=5 os_prio=0 tid=0x00007f024c009800 nid=0x365c in Object.wait() [0x00007f0254768000] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d6dddf40> (a test.WaitingTest$1) at java.lang.Thread.join(Thread.java:1253) - locked <0x00000000d6dddf40> (a test.WaitingTest$1) at test.WaitingTest.main(WaitingTest.java:25) Locked ownable synchronizers: - None3.Thread.sleep 代码：
public static void main(String[] args) throws InterruptedException { Thread.currentThread().sleep(1000 * 500);}jstack:
"main" #1 prio=5 os_prio=0 tid=0x00007f54a8009800 nid=0x36eb waiting on condition [0x00007f54ae463000] java.lang.Thread.State: TIMED_WAITING (sleeping) at java.lang.Thread.sleep(Native Method) at test.WaitingTest.main(WaitingTest.java:8) Locked ownable synchronizers: - None4.LockSupport.parkNanos(time) 和 LockSupport.parkUntil(time) 两个方法类似 代码：
public static void main(String[] args) throws InterruptedException { LockSupport.parkNanos(Long.MAX_VALUE);}jstack:
"main" #1 prio=5 os_prio=0 tid=0x00007eff98009800 nid=0x37b6 waiting on condition [0x00007effa0141000] java.lang.Thread.State: TIMED_WAITING (parking) at sun.misc.Unsafe.park(Native Method) at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:338) at test.WaitingTest.main(WaitingTest.java:8) Locked ownable synchronizers: - None BLOCKED状态BLOCKED状态，表示线程正在等待监视器锁。我们可以通过一个死锁的例子来分析。 例子很简单，程序中有两个Waiter线程，WaiterA和WaitB，它们都需要获取两个锁：lock_1和lock_2,但是它们获取锁的顺序不同，因此导致了死锁。 代码：
public class WaitingTest { private static Object lock_1 = new Object(); private static Object lock_2 = new Object(); public static void main(String[] args) throws InterruptedException { new WaiterA().start(); new WaiterB().start(); } static class WaiterA extends Thread { @Override public void run() { // 先获取lock_1,然后再获取lock_2 synchronized (lock_1) { System.out.println("lock1 get,wait to get lock2"); try { Thread.sleep(3 * 1000); } catch (InterruptedException e1) { } synchronized (lock_2) { System.out.println("lock2 get"); try { Thread.sleep(1000 * 50); } catch (InterruptedException e) { e.printStackTrace(); } } } } } static class WaiterB extends Thread { @Override public void run() { // 先获取lock_2,然后再获取lock_1 synchronized (lock_2) { System.out.println("lock2 get,wait to get lock1"); synchronized (lock_1) { System.out.println("lock1 get"); try { Thread.sleep(1000 * 50); } catch (InterruptedException e) { e.printStackTrace(); } } } } }}jstack:
"Thread-1" #10 prio=5 os_prio=0 tid=0x00007f0d800dc800 nid=0x39da waiting for monitor entry [0x00007f0d47bfa000] java.lang.Thread.State: BLOCKED (on object monitor) at test.WaitingTest$WaiterB.run(WaitingTest.java:47) - waiting to lock <0x00000000d6ddc510> (a java.lang.Object) - locked <0x00000000d6ddc520> (a java.lang.Object) Locked ownable synchronizers: - None"Thread-0" #9 prio=5 os_prio=0 tid=0x00007f0d800da800 nid=0x39d9 waiting for monitor entry [0x00007f0d47cfb000] java.lang.Thread.State: BLOCKED (on object monitor) at test.WaitingTest$WaiterA.run(WaitingTest.java:27) - waiting to lock <0x00000000d6ddc520> (a java.lang.Object) - locked <0x00000000d6ddc510> (a java.lang.Object) Locked ownable synchronizers: - None可以看到，上面Thread-1 和Thread-0的状态都是Blocked，原因是它们都在等待监视器锁，而Thread-1 已经获取到了锁0x00000000d6ddc520，正在等待获取0x00000000d6ddc510锁，而0x00000000d6ddc510锁已经被Thread-0获取到了，Thread-0反过来又正在等待获取0x00000000d6ddc520，而这个锁又被Thread-1获取了。 在jstack的最后，还有如下信息：
Found one Java-level deadlock:============================="Thread-1": waiting to lock monitor 0x00007f0d50004ed8 (object 0x00000000d6ddc510, a java.lang.Object), which is held by "Thread-0""Thread-0": waiting to lock monitor 0x00007f0d500062c8 (object 0x00000000d6ddc520, a java.lang.Object), which is held by "Thread-1"Java stack information for the threads listed above:==================================================="Thread-1": at test.WaitingTest$WaiterB.run(WaitingTest.java:47) - waiting to lock <0x00000000d6ddc510> (a java.lang.Object) - locked <0x00000000d6ddc520> (a java.lang.Object)"Thread-0": at test.WaitingTest$WaiterA.run(WaitingTest.java:27) - waiting to lock <0x00000000d6ddc520> (a java.lang.Object) - locked <0x00000000d6ddc510> (a java.lang.Object)Found 1 deadlock.就是说，已经发现了一个死锁，还有就是关于死锁的详细说明。
RUNNABLE状态我们写一个BIO的server端，server端绑定一个端口，并通过accept()方法等待客户端链接。 代码：
public static void main(String[] args) throws InterruptedException, IOException { ServerSocket serverSocket = new ServerSocket(9999); while (true) { Socket socket = serverSocket.accept(); // do something else // .... } }jstack:
"main" #1 prio=5 os_prio=0 tid=0x00007f4b58009800 nid=0x3ab8 runnable [0x00007f4b5ff64000] java.lang.Thread.State: RUNNABLE at java.net.PlainSocketImpl.socketAccept(Native Method) at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409) at java.net.ServerSocket.implAccept(ServerSocket.java:545) at java.net.ServerSocket.accept(ServerSocket.java:513) at test.WaitingTest.main(WaitingTest.java:16) Locked ownable synchronizers: - None可以看到，此时虽然程序在等待客户端接入，但是程序状态依然是RUNNABLE的。
TERMINATED和NEW状态这两个状态分别表示线程生命终结和生命开始，在jstack中没有对应的信息显示。
总结： WAITING和TIMED_WAITING的主要不同就在于后者在等待的时候设置了超时时间通过Object.wait，Thread.join两种方式进入的WAITING或者TIMED_WAITING,通过jstack查看显示的都是wait on monitor,而通过其他方式（Thread.sleep,LockSupport等）进入的WAITING或者TIMED_WAITING,通过jstack查看显示的都是waiting on condition。BLOCKED状态，通过jstack查看，显示的是waiting for monitor entry，注意与WAITING和TIMED_WAITING的区别。java线程通过不同的方法调用进入不同的状态，下面图描述的很清楚：
顺便推荐个很好的网站： Java中的UML图：http://www.uml-diagrams.org/examples/java-uml-examples.html
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