qt中waitForReadyRead和waitForBytesWritten函数的使用

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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队列中排队等待执行）一直在消队列中疯狂阻塞，阻塞的结果就是消队列不断膨胀，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！

本文标签： 函数QTwaitForReadyReadwaitForBytesWritten