Qmutex/QThread PyQt problem

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Hello,

I have a problem with getting my thread to work correctly in pyqt. I also dont really understand mutex and where to use it correctly. I have attached my code.

The short:
I select a file that will get tailed.
Once I click start a QTimer is activated to check for new files every 5 seconds to handle rollovers. (If there is another way to do this pray tell!)

Anyways It works the first time that the program runs through but after that it complains about a RuntimeError: underlying C/C++ object has been deleted.

Any help would be extremely appreciated!! Even if someone could maybe just paste me some py
qt code that uses threads and mutexs' so I can get a general idea. There seems to be a very big void on google regarding the subject :-(

Regards!