[GRASS-dev] [GRASS GIS] #943: wxpython gui hangs after switching to cairo display driver

[GRASS GIS]

#943: wxpython gui hangs after switching to cairo display driver
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 Reporter:  epatton                       |       Owner:  grass-dev@…              
     Type:  defect                        |      Status:  new                      
 Priority:  critical                      |   Milestone:  6.4.3                    
Component:  wxGUI                         |     Version:  svn-develbranch6         
 Keywords:  cairo, driver, gui, wxpython  |    Platform:  Linux                    
      Cpu:  All                           |  
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Comment(by hamish):

 by adding a little debug write to d.mon just before its final exit(), I
 can see that the module was completing ok; i.e. not getting hung up in the
 G_spawn(). But then something is still holding it open and it becomes a
 zombie until you manually stop the cairo driver process. At which point it
 releases and all is back to normal (except wxgui mouse cursor remains an
 hourglass)

 doing the same thing from the command line works fine.

 if it was some "Graphics driver [cairo] started" text from d.mon waiting
 to be flushed from the stderr buffer by python's popen.communicate(), then
 for one thing the proc.communicate() should flush it, and for another why
 would externally stopping the cairo driver suddenly free it?

 Glynn wrote:
 > Terminating a process implicitly close()s all open file descriptors,
 > but the underlying object (file, socket, etc) isn't actually closed
 > until no process has it open.

 is there a chance that the G_spawn()'d `mon.start` or `mon.select` program
 has gotten a hold of one of the stdin/out/err pipes, and is holding it
 open, and then in the wxgui the proc.communicate() can't let its end go
 until that happens?

 but in that case perhaps the zombie wouldn't exist? since the zombie
 exists perhaps it is d.mon's exit() which can't let go of the pipe?


 thanks,
 Hamish

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Ticket URL: <https://trac.osgeo.org/grass/ticket/943#comment:19>
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