Fix thread-related plotting crash on Linux.

Plotter.notify was called from the fitting thread.  This caused
hard crash when plot windows were updated during refinement.

Solution: Use thread-safe postEvent function to request plot updates.

Author: pavoljuhas

diffpy/pdfgui/control/calculation.py

@@ -130,12 +130,7 @@ def start(self):
         gui = self.owner.controlCenter.gui
         if gui:
             gui.postEvent(gui.OUTPUT, None)
-            try:
-                gui.lock()
-                for plot in self.owner.controlCenter.plots:
-                    plot.notify(self)
-            finally:
-                gui.unlock()
+            gui.postEvent(gui.PLOTNOW, self)
         return
 
     def calculate(self):

diffpy/pdfgui/control/fitting.py

@@ -723,14 +723,7 @@ def refine_step(self):
         gui = self.controlCenter.gui
         if gui:
             gui.postEvent(gui.OUTPUT, None)
-        try:
-            if gui:
-                gui.lock()
-            for plot in self.controlCenter.plots:
-                plot.notify(self)
-        finally:
-            if gui:
-                gui.unlock()
+            gui.postEvent(gui.PLOTNOW, self)
 
         if finished:
             self.res = "* %s\n\n"%time.ctime()+ self.server.save_res_string()

diffpy/pdfgui/gui/mainframe.py

@@ -286,6 +286,7 @@ def __customProperties(self):
         self.ERROR = 1
         self.UPDATE = 1<<1
         self.OUTPUT = 1<<2
+        self.PLOTNOW = 1<<3
 
         # Needed for the error checker so it doesn't throw errors at quit time
         self.quitting = False
@@ -2472,6 +2473,11 @@ def onCustom(self, event):
             self.updateFittingStatus(job)
         elif event.type == self.OUTPUT:
             self.updateOutput()
+        elif event.type == self.PLOTNOW:
+            # job is a fitting or a calculation with a new data to plot.
+            job = event.info
+            for plot in self.control.plots:
+                plot.notify(job)
         return
 
     def updateFittingStatus(self, job):