Why my object stay in main thread?

[honestapple]

Yes, it is QtSerialPort library.

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Added after 26 minutes:

Yes, I knew that you have mention that. I am doing a USB DAQ GUI part on PC using QT4.8.6+QWT6.0.2 under Windows XP. I should receive data from device and display waveform, frequency spectrum, etc. I have made a demo without threads which could receive and send command( using timer ) at a interval, but I could not display the wavefrom in realtime. In fact, it was not that the waveform could not be displayed completly. It is sometimes good, sometimes bad. When it was bad, I knew that there are something wrong with the QwtCPointerData. Because there are many operation in main GUI thread, I wanted to tried to use monitor thread to release GUI thread from doing data receiving and sending command.