/*package*/ Handler target;

/*package*/ Runnable callback;

public int what;

public Object obj;

  // sometimes we store linked lists of these things

/*package*/ Message next;

    private static final Object sPoolSync = new Object();

    private static Message sPool;

private static int sPoolSize = 0;

    private static final int MAX_POOL_SIZE = 50;

public Message() {

    }

   public static Message obtain() {

        synchronized (sPoolSync) { //对一个变量进行加锁，进行同步控制

            if (sPool != null) {  //若不为空，则在消息池中取出空消息

                Message m = sPool;

                sPool = m.next;

                m.next = null;

                m.flags = 0; // clear in-use flag

                sPoolSize--;

                return m;

            }

        }

        return new Message();

    }

   /**

     * Sends this Message to the Handler specified by {@link #getTarget}.

     * Throws a null pointer exception if this field has not been set.

     */

    public void sendToTarget() {

        target.sendMessage(this);

    }

    public static Message obtain(Handler h, int what) {

        Message m = obtain();

        m.target = h;

        m.what = what;

        return m;

    }

/**

     * Same as {@link #obtain()}, but sets the values of the target, what, and obj

     * members.

     * @param h  The target value to set.

     * @paramwhat  The what value to set.

     * @paramobj  The object method to set.

     * @return  A Message object from the global pool.

     */

    public static Message obtain(Handler h, int what, Object obj) {

        Message m = obtain();

        m.target = h;

        m.what = what;

        m.obj = obj;

        return m;

    }