qt中waitForReadyRead和waitForBytesWritten函数的使用

一些见解
官方文档介绍

Blocks until new data is available for reading and the readyRead() signal has been emitted, or until msecs milliseconds have passed. If msecs is -1, this function will not time out.
Returns true if new data is available for reading; otherwise returns false (if the operation timed out or if an error occurred).
This function can operate without an event loop. It is useful when writing non-GUI applications and when performing I/O operations in a non-GUI thread.
If called from within a slot connected to the readyRead() signal, readyRead() will not be reemitted.
Reimplement this function to provide a blocking API for a custom device. The default implementation does nothing, and returns false.
Warning: Calling this function from the main (GUI) thread might cause your user interface to freeze.

文档没有直接说明会产生error信号：
在超时的时候会触发error(QAbstractSocket::SocketError)信号（SocketTimeoutError），一不注意可能就会产生一个bug
举例：

//尝试在waitForReadyRead()函数之前有数据过来，当执行wait函数时，会直接返回true。
//在阻塞期间来数据，会返回true。
//阻塞默认参数30000ms，超时返回false。

while (written != data.size())
{
if (mSocket->waitForBytesWritten())
{
written += mSocket->write(data.mid(written, data.size() - written));
}
}

if (port.waitForReadyRead(10)) 
    {
        port->readAll();
     }

因为waitfor系列函数是通过readyRead()信号与bytesWritten()信号来实现的，如果产生这两个信号过快（就像上面的代码，死循环执行疯狂产生信号），会导致对应到槽函数的事件（信号到槽的执行是一种事件，这个事件将会到对应线程的消息队列中排队等待执行）一直在消息队列中疯狂阻塞，阻塞的结果就是消息队列不断膨胀，从而内存不断增加，直到队列到达上限导致程序崩溃。
一定要注意超时的问题！