android 进程/线程管理（一）----消息机制的框架

public final boolean post(Runnable r)
{
return sendMessageDelayed(getPostMessage(r), 0);
}

public final boolean postAtTime(Runnable r, long uptimeMillis)

public final boolean postAtTime(Runnable r, Object token, long uptimeMillis)

private static Message getPostMessage(Runnable r) {
        Message m = Message.obtain();
        m.callback = r;
        return m;
    }

/**
 * A Handler allows you to send and process {@link Message} and Runnable
 * objects associated with a thread's {@link MessageQueue}.  Each Handler
 * instance is associated with a single thread and that thread's message
 * queue.  When you create a new Handler, it is bound to the thread /
 * message queue of the thread that is creating it -- from that point on,
 * it will deliver messages and runnables to that message queue and execute
 * them as they come out of the message queue.
*
 * <p>There are two main uses for a Handler: (1) to schedule messages and
 * runnables to be executed as some point in the future; and (2) to enqueue
 * an action to be performed on a different thread than your own.
*
 * <p>When posting or sending to a Handler, you can either
 * allow the item to be processed as soon as the message queue is ready
 * to do so, or specify a delay before it gets processed or absolute time for
 * it to be processed.  The latter two allow you to implement timeouts,
 * ticks, and other timing-based behavior.
*/

public void dispatchMessage(Message msg) 分发消息
public void handleMessage(Message msg)   处理消息，该方法通常情况下，须由子类继承。

public void dispatchMessage(Message msg) {
        if (msg.callback != null) {
            handleCallback(msg);
        } else {
            if (mCallback != null) {
                if (mCallback.handleMessage(msg)) {
                    return;
                }
            }
            handleMessage(msg);
        }
    }

public Handler(Looper looper, Callback callback, boolean async) {
        mLooper = looper;  mQueue = looper.mQueue; mCallback = callback;
        mAsynchronous = async;
    }

private Looper(boolean quitAllowed) {
        mQueue = new MessageQueue(quitAllowed);
        mThread = Thread.currentThread();
    }

// sThreadLocal.get() will return null unless you've called prepare().
    static final ThreadLocal<Looper> sThreadLocal = new ThreadLocal<Looper>();

private static void prepare(boolean quitAllowed) {
        if (sThreadLocal.get() != null) {
            throw new RuntimeException("Only one Looper may be created per thread");
        } sThreadLocal.set(new Looper(quitAllowed)); }

/**
     * Run the message queue in this thread. Be sure to call
     * {@link #quit()} to end the loop.
     */
    public static void loop() {
        final Looper me = myLooper();
        if (me == null) {
            throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
        }
        final MessageQueue queue = me.mQueue;

        // Make sure the identity of this thread is that of the local process,
        // and keep track of what that identity token actually is.
        Binder.clearCallingIdentity();
        final long ident = Binder.clearCallingIdentity();

        for (;;) {
            Message msg = queue.next(); // might block
            if (msg == null) {
                // No message indicates that the message queue is quitting.
                return;
            }

            // This must be in a local variable, in case a UI event sets the logger
            Printer logging = me.mLogging;
            if (logging != null) {
                logging.println(">>>>> Dispatching to " + msg.target + " " +
                        msg.callback + ": " + msg.what);
            }

            msg.target.dispatchMessage(msg);

            if (logging != null) {
                logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
            }

            // Make sure that during the course of dispatching the
            // identity of the thread wasn't corrupted.
            final long newIdent = Binder.clearCallingIdentity();
            if (ident != newIdent) {
                Log.wtf(TAG, "Thread identity changed from 0x"
                        + Long.toHexString(ident) + " to 0x"
                        + Long.toHexString(newIdent) + " while dispatching to "
                        + msg.target.getClass().getName() + " "
                        + msg.callback + " what=" + msg.what);
            }

            msg.recycle();
        }
    }

Message msg = queue.next(); // might block
            if (msg == null) {
                // No message indicates that the message queue is quitting.
                return;
            }

public static void main(String[] args) {
    ...

    Looper.prepareMainLooper();

    if (sMainThreadHandler == null) {
            sMainThreadHandler = thread.getHandler();
        }

    Looper.loop();
}

private static Looper sMainLooper;  // guarded by Looper.class