Need concurrency advice with callback function

[BreakBad]

(PyQt 4.8, Python 2.7)
After reading through the following I'm still left a bit puzzled as to which approach to attempt to utilize for my situation. Any advice would be appreciated.
Keeping_the_GUI_Responsive

I have a module, flp.so library to which I have no control over. It takes a function as a constructor argument, and performs a complex/long calculation when invoking the run() method. Here I subclassed QThread, and invoke flp.run inside the thread's run method. In turn the flp module will invoke the callback method, which emits a signal. I catch the signal back in my main thread, and update a model for a QTreeView and update a QProgressBar.

def my_runner(QThread):
    def __init__(self,callback=None):
        self.callback = callback
 
    def callback(self):
        # f_runner.f_output is array that is appended every iteration of f_runner.run()
        emit(SIGNAL('update_main'),self.f_runner.f_output.pop())
 
    def run(self):
        import flp
        self.f_runner = flp.f_runner(callback=self.callback)
        self.f_runner.run()

def my_runner(QThread):
    def __init__(self,callback=None):
        self.callback = callback

    def callback(self):
        # f_runner.f_output is array that is appended every iteration of f_runner.run()
        emit(SIGNAL('update_main'),self.f_runner.f_output.pop())

    def run(self):
        import flp
        self.f_runner = flp.f_runner(callback=self.callback)
        self.f_runner.run()

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However, the GUI is not very responsive, as the signals are probably stacking up and the events can't be processed fast enough. I try to avoid invoking QApplication.processEvents(), but tried it here and very bad things happen.

I have been rethinking this design but have gotten stuck. Eventually I would like the main thread GUI to be responsive while this thread is working and updating the progress bar and table view in the main.

TYVM for reading.