线程的状态

Thread.State首先看JDK中的代码: java.lang.Thread.State /** * A thread state. A thread can be in one of the following states: * 一个线程的状态，一个线程可以处于以下状态中的某一个状态 * <ul> * <li>{@link #NEW} * A thread that has not yet started is in this state. * </li> * <li>{@link #RUNNABLE} * A thread executing in the Java virtual machine is in this state. * </li> * <li>{@link #BLOCKED} * A thread that is blocked waiting for a monitor lock * is in this state. * </li> * <li>{@link #WAITING} * A thread that is waiting indefinitely for another thread to * perform a particular action is in this state. * </li> * <li>{@link #TIMED_WAITING} * A thread that is waiting for another thread to perform an action * for up to a specified waiting time is in this state. * </li> * <li>{@link #TERMINATED} * A thread that has exited is in this state. * </li> * </ul> * * * A thread can be in only one state at a given point in time. * These states are virtual machine states which do not reflect * any operating system thread states. * * @since 1.5 * @see #getState / public enum State { /* * Thread state for a thread which has not yet started. / NEW, /* * Thread state for a runnable thread. A thread in the runnable * state is executing in the Java virtual machine but it may * be waiting for other resources from the operating system * such as processor. / RUNNABLE, /* * Thread state for a thread blocked waiting for a monitor lock. * A thread in the blocked state is waiting for a monitor lock * to enter a synchronized block/method or * reenter a synchronized block/method after calling * {@link Object#wait() Object.wait}. / BLOCKED, /* * Thread state for a waiting thread. * A thread is in the waiting state due to calling one of the * following methods: * <ul> * <li>{@link Object#wait() Object.wait} with no timeout</li> * <li>{@link #join() Thread.join} with no timeout</li> * <li>{@link LockSupport#park() LockSupport.park}</li> * </ul> * * A thread in the waiting state is waiting for another thread to * perform a particular action. * * For example, a thread that has called <tt>Object.wait()</tt> * on an object is waiting for another thread to call * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on * that object. A thread that has called <tt>Thread.join()</tt> * is waiting for a specified thread to terminate. / WAITING, /* * Thread state for a waiting thread with a specified waiting time. * A thread is in the timed waiting state due to calling one of * the following methods with a specified positive waiting time: * <ul> * <li>{@link #sleep Thread.sleep}</li> * <li>{@link Object#wait(long) Object.wait} with timeout</li> * <li>{@link #join(long) Thread.join} with timeout</li> * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li> * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li> * </ul> / TIMED_WAITING, /* * Thread state for a terminated thread. * The thread has completed execution. */ TERMINATED; }1、新建(New)新创建了一个线程对象，还未调用start()方法。2、就绪（Runnable）线程对象创建后，其他线程(比如main线程）调用了该对象的start()方法。该状态的线程位于可运行线程池中，等待被线程调度选中获取cpu 的使用权。3、运行中（Running，线程状态中并没有这一状态，但是实际执行中是有的）可运行状态(runnable)的线程获得了cpu 时间片（timeslice），执行程序代码。4、限期等待（Timed Waiting）也可以称作 TIMED_WAITING（有等待时间的等待状态）。线程主动调用以下方法：Thread.sleep方法；Object的wait方法，带有时间；Thread.join方法，带有时间；LockSupport的parkNanos方法，带有时间。5、无限期等待（Waiting）运行中（Running）的线程执行了以下方法：Object的wait方法，并且没有使用timeout参数;Thread的join方法，没有使用timeout参数；LockSupport的park方法；Conditon的await方法。6、阻塞（Blocked）阻塞状态是指线程因为某种原因放弃了cpu 使用权，暂时停止运行。直到线程进入可运行(runnable)状态，才有机会再次获得cpu timeslice 转到运行(running)状态。阻塞的情况分两种：同步阻塞：运行(running)的线程进入了一个synchronized方法，若该同步锁被别的线程占用，则JVM会把该线程放入锁池(lock pool)中。其他阻塞：运行(running)的线程发出了I/O请求时，JVM会把该线程置为阻塞状态。当I/O处理完毕时，线程重新转入可运行(runnable)状态。7、结束（Terminated）线程run()、main() 方法执行结束，或者因异常退出了run()方法，则该线程结束生命周期。线程状态探秘jstack查看线程状态jstack -l <pid> 即可察看线程状态，如何使用呢？随便写一个死循环看一下public class TestThreadState { public static void main(String[] args) { for (; ; ) { } }}ps -ef|grep TestThreadState，找到对应的pid，jstack -l <pid>即可，如果未输出线程信息，可以尝试使用-F参数来强制输出。“main” #1 prio=5 os_prio=31 tid=0x00007f8194801800 nid=0x1603 runnable [0x000070000a9b4000] java.lang.Thread.State: RUNNABLE at org.java.bin.TestThreadState.main(TestThreadState.java:12)