FIX: macosx, clear pending timers when the figure is destroyed

Running the macosx backend without calling show() would cause
Timers to pile up and not fire because the event loop was not running.
This leaked objects when closing/opening multiple figures. To fix this,
we keep track of the timers on the canvas and remove all of the pending
timers when destroying the figure to clear all back-references.

Author: greglucas

lib/matplotlib/backends/backend_macosx.py

@@ -37,6 +37,8 @@ def __init__(self, figure):
         super().__init__(figure=figure)
         self._draw_pending = False
         self._is_drawing = False
+        # Keep track of the timers that are alive
+        self._timers = set()
 
     def draw(self):
         """Render the figure and update the macosx canvas."""
@@ -59,14 +61,16 @@ def draw_idle(self):
 
     def _single_shot_timer(self, callback):
         """Add a single shot timer with the given callback"""
-        # We need to explicitly stop (called from delete) the timer after
+        # We need to explicitly stop and remove the timer after
         # firing, otherwise segfaults will occur when trying to deallocate
         # the singleshot timers.
         def callback_func(callback, timer):
             callback()
-            del timer
+            self._timers.remove(timer)
+            timer.stop()
         timer = self.new_timer(interval=0)
         timer.add_callback(callback_func, callback, timer)
+        self._timers.add(timer)
         timer.start()
 
     def _draw_idle(self):
@@ -150,6 +154,14 @@ def _close_button_pressed(self):
         Gcf.destroy(self)
         self.canvas.flush_events()
 
+    def destroy(self):
+        # We need to clear any pending timers that never fired, otherwise
+        # we get a memory leak from the timer callbacks holding a reference
+        while self.canvas._timers:
+            timer = self.canvas._timers.pop()
+            timer.stop()
+        super().destroy()
+
     @classmethod
     def start_main_loop(cls):
         _macosx.show()