I think you are going for the whole thing wrong First you are assuming that by the time you receive readyRead() all the data you need will be available, which is incorrect, only part of it may be there. And to overcome this issue you should read the data from the port when it comes in and only when there is enough to process it, signal the wait condition. This way you'll get rid of two problems at once. And no need to disconnect signals.

Next thing - by groupping everything into one object, your program has become everything but a good designed object oriented application. Instead of aggregating, separate the data used by different tasks. Make them two classes containing only the data they need. There is a question whether you need the threads at all - from what I see, you don't, you can do everything in one thread. Once you have clear design, everything will become easier.