public static WindowManagerService main(final Context context, final InputManagerService im,final boolean showBootMsgs, final boolean onlyCore, WindowManagerPolicy policy,ActivityTaskManagerService atm, Supplier<SurfaceControl.Transaction> transactionFactory,Supplier<Surface> surfaceFactory,
            Function<SurfaceSession, SurfaceControl.Builder> surfaceControlFactory) {
        DisplayThread.getHandler().runWithScissors(() ->
                sInstance = new WindowManagerService(context, im, showBootMsgs, onlyCore, policy,
                        atm, transactionFactory, surfaceFactory, surfaceControlFactory), 0);
        return sInstance;
}

public final boolean runWithScissors(@NonNull Runnable r, long timeout) {
    if (r == null) {
        throw new IllegalArgumentException("runnable must not be null");
    }
    if (timeout < 0) {
        throw new IllegalArgumentException("timeout must be non-negative");
    }
    if (Looper.myLooper() == mLooper) {
        r.run();
        return true;
    }
    BlockingRunnable br = new BlockingRunnable(r);
    return br.postAndWait(this, timeout);
}

private static final class BlockingRunnable implements Runnable {
    private final Runnable mTask;
    private boolean mDone;
    public BlockingRunnable(Runnable task) {
        mTask = task;
    }
    @Override
    public void run() {
        try {
            mTask.run();//運行在 handler 線程
        } finally {
            synchronized (this) {
                mDone = true; //標記完成
                notifyAll(); //喚醒線程
            }
        }
    }
    public boolean postAndWait(Handler handler, long timeout) {
        //使用 post 進行發(fā)送
        if (!handler.post(this)) {
            return false;
        }
        synchronized (this) {
            if (timeout > 0) {
                final long expirationTime = SystemClock.uptimeMillis() + timeout;
                while (!mDone) {
                    long delay = expirationTime - SystemClock.uptimeMillis();
                    if (delay <= 0) {
                        return false; // timeout
                    }
                    try {
                        wait(delay);
                    } catch (InterruptedException ex) {
                    }
                }
            } else {
                while (!mDone) {
                    try {
                        wait();
                    } catch (InterruptedException ex) {
                    }
                }
            }
        }
        return true;
    }
}