Java多线程状态切换

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线程状态

• NEW
• RUNNABLE
• BLOCKED
• WAITING
• TIMED_WAITING
• TERMINATED

参考JDK源码Thread.java中的State枚举类

 /**
  * A thread state.  A thread can be in one of the following states:
  * <ul>
  * <li>{@link #NEW}<br>
  *     A thread that has not yet started is in this state.
  *     </li>
  * <li>{@link #RUNNABLE}<br>
  *     A thread executing in the Java virtual machine is in this state.
  *     </li>
  * <li>{@link #BLOCKED}<br>
  *     A thread that is blocked waiting for a monitor lock
  *     is in this state.
  *     </li>
  * <li>{@link #WAITING}<br>
  *     A thread that is waiting indefinitely for another thread to
  *     perform a particular action is in this state.
  *     </li>
  * <li>{@link #TIMED_WAITING}<br>
  *     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}<br>
  *     A thread that has exited is in this state.
  *     </li>
  * </ul>
  *
  * <p>
  * 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>
      *
      * <p>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;
 } 

线程状态切换图

Note：

阻塞状态是线程因为某种原因放弃CPU使用权，暂时停止运行。直到线程进入就绪状态，才有机会转到运行状态。阻塞的情况分三种：

1. 等待阻塞：运行的线程执行wait()方法，JVM会把该线程放入等待池中。(wait会释放持有的锁)
2. 同步阻塞：运行的线程在获取对象的同步锁时，若该同步锁被别的线程占用，则JVM会把该线程放入锁池中。
3. 其他阻塞：运行的线程执行sleep()或join()方法，或者发出了I/O请求时，JVM会把该线程置为阻塞状态。当sleep()状态超时、join()等待线程终止或者超时、或者I/O处理完毕时，线程重新转入就绪状态。