Break reference cycle Line2D <-> Line2D._lineFunc.

anntzer · anntzer · commit 353275c53efb · 2016-07-24T02:35:38.000-07:00
Upon drawing, Line2D objects would store a reference to one of their own bound methods as their `_lineFunc` argument. This would lead to them being gc'ed not when going out of scope, but only when the "true" gc kicks in; additionally this led to some pickle-related bugs (#3627). One can easily sidestep this problem by not storing this bound method. To check the behavior, try (py3.4+ only): ``` import gc import weakref from matplotlib import pyplot as plt def f(): fig, ax = plt.subplots() img = ax.imshow([[0, 1], [2, 3]]) weakref.finalize(img, print, "gc'ing image") l, = plt.plot([0, 1]) weakref.finalize(l, print, "gc'ing line") fig.canvas.draw() img.remove() l.remove() f() print("we have left the function") gc.collect() print("and cleaned up our mess") ``` Before the patch, the AxesImage is gc'ed when the function exits but the Line2D only upon explicit garbage collection. After the patch, both are collected immediately.
diff --git a/lib/matplotlib/lines.py b/lib/matplotlib/lines.py
@@ -445,12 +445,6 @@ def __init__(self, xdata, ydata,
 
         self.set_data(xdata, ydata)
 
-    def __getstate__(self):
-        state = super(Line2D, self).__getstate__()
-        # _linefunc will be restored on draw time.
-        state.pop('_lineFunc', None)
-        return state
-
     def contains(self, mouseevent):
         """
         Test whether the mouse event occurred on the line.  The pick
@@ -784,7 +778,7 @@ def draw(self, renderer):
         if funcname != '_draw_nothing':
             tpath, affine = transf_path.get_transformed_path_and_affine()
             if len(tpath.vertices):
-                self._lineFunc = getattr(self, funcname)
+                line_func = getattr(self, funcname)
                 gc = renderer.new_gc()
                 self._set_gc_clip(gc)
 
@@ -807,7 +801,7 @@ def draw(self, renderer):
                 if self.get_sketch_params() is not None:
                     gc.set_sketch_params(*self.get_sketch_params())
 
-                self._draw_lines(renderer, gc, tpath, affine.frozen())
+                line_func(renderer, gc, tpath, affine.frozen())
                 gc.restore()
 
         if self._marker and self._markersize > 0:
@@ -1250,9 +1244,6 @@ def set_dashes(self, seq):
         else:
             self.set_linestyle((0, seq))
 
-    def _draw_lines(self, renderer, gc, path, trans):
-        self._lineFunc(renderer, gc, path, trans)
-
     def _draw_solid(self, renderer, gc, path, trans):
         gc.set_linestyle('solid')
         gc.set_dashes(self._dashOffset, self._dashSeq)
diff --git a/lib/matplotlib/tests/test_pickle.py b/lib/matplotlib/tests/test_pickle.py
@@ -236,7 +236,7 @@ def test_grid():
     fig = manager.canvas.figure
     ax = fig.add_subplot(1, 1, 1)
     ax.grid()
-    # Drawing the grid triggers instance methods to be attached
+    # Drawing the grid used to trigger instance methods to be attached
     # to the Line2D object (_lineFunc).
     manager.canvas.draw()
 
