I've been struggling with my Python application and I can't find any answers.
I'm having PyQT GUI application which uses Matplotlib widget. GUI starts a new thread which handles plotting to mpl widget. I'm afraid I run now to a race condition by accessing matplotlib drawing components from another thread which leads to crash.
This is basically, what my code looks like:
class Analyzer(QMainWindow, Ui_MainWindow):
def __init__(self, parent=None):
self.timer = QTimer()
super(Analyzer, self).__init__(parent)
self.setupUi(self)
self.background = self.mpl.canvas.copy_from_bbox(self.mpl.canvas.ax.bbox)
self.plotQueue = Queue.Queue()
self.plotterStarted = False
self.plotter = Plotter(self.mpl, self.plotQueue)
self.cam = Cam(self.plotQueue, self.textEdit)
...
class Ui_MainWindow(object):
def setupUi(self, MainWindow):
...
self.mpl = MplWidget(self.centralWidget)
...
class MplWidget(QtGui.QWidget):
"""Widget defined in Qt Designer"""
def __init__(self, parent = None):
QtGui.QWidget.__init__(self, parent)
self.canvas = MplCanvas()
...
class MplCanvas(FigureCanvas):
"""Class to represent the FigureCanvas widget"""
def __init__(self):
# setup Matplotlib Figure and Axis
self.fig = Figure()
self.ax = self.fig.add_subplot(111)
# initialization of the canvas
FigureCanvas.__init__(self, self.fig)
FigureCanvas.updateGeometry(self)
And plotter class:
class Plotter():
def __init__(self, mpl="", plotQueue=""):
self.mpl = mpl
self.background = self.mpl.canvas.copy_from_bbox(self.mpl.canvas.ax.bbox)
self.plotQueue = plotQueue
...
def start(self):
threading.Thread(target=self.run).start()
''' Real time plotting '''
def run(self):
while True:
try:
inputData = self.plotQueue.get(timeout=1)
# Go through samples
for samples in inputData:
self.line, = self.mpl.canvas.ax.plot(x, y, animated=True, label='Jee')
for sample in samples:
x.append(sample['tick'])
y.append(sample['linear'])
self.line.set_data(x,y)
self.mpl.canvas.ax.draw_artist(self.line)
self.mpl.canvas.blit(self.mpl.canvas.ax.bbox)
...
So I pass mpl and plotQueue to Plotter class object. PlotQueue is populated in Cam class which processes incoming data from external hw. Plotter reads the plotQueue, processes it and calls drawing for mpl.
But is this a thread safe method to access mpl? If not, how should I do it? Any tips on this are appreciated.
Edit 1.
I added QTimer in main thread to handle drawing, as suggested in comments. After a small tweaking, I got it working fairly well.
class Analyzer(...):
def __init__(self, parent=None):
QObject.connect(self.timer, SIGNAL("timeout()"), self.periodicCall)
def periodicCall(self):
self.plotter.draw()
def startButton(self):
self.timer.start(10)
Thanks a lot for useful comments.
