Non blocking pyplot GUI for GDB python pretty printer

Hi, all.
I'm using matplotlib as a GDB pretty printer to visualize the data under Windows XP.
Is it possible to open a plot window which does not block the GDB's command line prompt?
I try to put the mainloop (show() function) in a separate thread, but this cause some GDB hanging issue if I try to show the plot window in the second time.
A minimal testing shows that a normal Tk window don't have this issue.
See my testing sample code in:

One of GDB developer Tom replied in the stackoverflow, he said that it is an issue related to SIGCHLD. I personally don't have a solution, so I'd ask for your help, thanks.