Qt:服务器端
TCP/IP助手:客户端
1)服务器端开始监听QTcpServer::Listen()
2)客户端连接服务器端
3)关闭服务器端QTcpServer::close()
4)服务器端又重新监听QTcpServer::Listen()
4)关闭客户端(实际上已经断了,至少助手没有显示关闭,所以必须先点击,再点击),又连接服务端
5)服务端崩溃,崩溃的地方在
qint64 QIODevice::write(const QByteArray &data)
{
    Q_D(QIODevice);  //这句崩了
    // Keep the chunk pointer for further processing in
    // QIODevicePrivate::write(). To reduce fragmentation,
    // the chunk size must be sufficiently large.
    if (data.size() >= QRINGBUFFER_CHUNKSIZE)
        d->currentWriteChunk = &data;
    const qint64 ret = write(data.constData(), data.size());
    d->currentWriteChunk = nullptr;
    return ret;
}