Java线程状态

在Thread类中，存在一个State枚举：

    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 {@code Object.wait()}
         * on an object is waiting for another thread to call
         * {@code Object.notify()} or {@code Object.notifyAll()} on
         * that object. A thread that has called {@code Thread.join()}
         * 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;
    }

通过该枚举可知道一个Thread具有6种状态：

1. NEW
   线程创建后，未启动时的状态

2. RUNNABLE
   可运行状态。处于该状态的线程正在JVM中执行，但可能在等待操作系统资源，比如处理器资源
   对于io方法，比如socket.getInputStream().read()方法，阻塞时，线程状态也是RUNNABLE

   "main" #1 prio=5 os_prio=0 cpu=171.88ms elapsed=7.02s tid=0x0000022bc7a3f400 nid=0x3f4c runnable  [0x00000086ab2ff000]
      java.lang.Thread.State: RUNNABLE
   	at sun.nio.ch.SocketDispatcher.read0(java.base@17.0.2/Native Method)
   	at sun.nio.ch.SocketDispatcher.read(java.base@17.0.2/SocketDispatcher.java:46)
   	at sun.nio.ch.NioSocketImpl.tryRead(java.base@17.0.2/NioSocketImpl.java:261)
   	at sun.nio.ch.NioSocketImpl.implRead(java.base@17.0.2/NioSocketImpl.java:312)
   	at sun.nio.ch.NioSocketImpl.read(java.base@17.0.2/NioSocketImpl.java:350)
   	at sun.nio.ch.NioSocketImpl$1.read(java.base@17.0.2/NioSocketImpl.java:803)
   	at java.net.Socket$SocketInputStream.read(java.base@17.0.2/Socket.java:966)
   	at java.io.InputStream.readNBytes(java.base@17.0.2/InputStream.java:409)
   	at java.io.InputStream.readAllBytes(java.base@17.0.2/InputStream.java:346)
   	at org.hzqisheng.ReadSocket.main(ReadSocket.java:15)
   

3. BLOCKED
   阻塞状态
   线程处于一个阻塞状态，等待监视器锁。
   等待进入synchronized块/代码的线程会进入BLOCKED状态。

4. WAITING
   等待状态
   调用以下方法会导致线程进入WAITING状态

   • 未指定timeout的Object.wait
   • 未指定timeout的Thread.join
   • LockSupport.park()

5. TIMED_WAITING
   指定了时间的等待状态
   调用以下方法会导致线程进入TIMED_WAITING状态

   • Thread.sleep
   • Object.wait带有超时时间
   • Thread.join带有超时时间
   • LockSupport.parkNanos
   • LockSupport.parkUntil

6. TERMINATED
   已停止的线程