執行緒狀態

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;
}

執行緒池狀態

// runState is stored in the high-order bits
private static final int RUNNING    = -1 << COUNT_BITS;
private static final int SHUTDOWN   =  0 << COUNT_BITS;
private static final int STOP       =  1 << COUNT_BITS;
private static final int TIDYING    =  2 << COUNT_BITS;
private static final int TERMINATED =  3 << COUNT_BITS;

• 執行緒池建立後處於RUNNING狀態。
• 呼叫shutdown()方法後處於SHUTDOWN狀態，執行緒池不能接受新的任務，清除一些空閒worker，會等待阻塞佇列的任務完成。
• 呼叫shutdownNow()方法後處於STOP狀態，執行緒池不能接受新的任務，中斷所有執行緒，阻塞佇列中沒有被執行的任務全部丟棄。此時，poolsize=0，阻塞佇列的size也為0。
• 當所有的任務已終止，ctl記錄的”任務數量”為0，執行緒池會變為TIDYING狀態。接著會執行terminated()函式。

ThreadPoolExecutor中有一個控制狀態的屬性叫ctl，它是一個AtomicInteger型別的變數。執行緒池狀態就是通過AtomicInteger型別的成員變數ctl來獲取的。獲取的ctl值傳入runStateOf方法，與~CAPACITY位與運算(CAPACITY是低29位全1的int變數)。~CAPACITY在這裡相當於掩碼，用來獲取ctl的高3位，表示執行緒池狀態；而另外的低29位用於表示工作執行緒數

附上runStateOf()方法，如下：

private static int runStateOf(int c)     { return c & ~CAPACITY; }

• 執行緒池處在TIDYING狀態時，執行完terminated()方法之後，就會由 TIDYING -> TERMINATED， 執行緒池被設定為TERMINATED狀態。