Fix cache overflow

Author: dappham-CODRA

qwt/text.py

@@ -234,6 +234,7 @@ def draw(self, painter, rect, flags, text):
 _FONT_TUPLE_CACHE: dict = {}  # tuple_key -> tuple_key (interning, also acts
 #                              as the "have we seen this logical font" set)
 _FONT_KEY_CACHE_LIMIT = 1024
+_FM_CACHE_LIMIT = 256  # max QFontMetrics/QFontMetricsF entries per engine
 
 
 def _font_tuple_key(font):
@@ -317,13 +318,17 @@ def fontmetrics(self, font):
         try:
             return self._fm_cache[fid]
         except KeyError:
+            if len(self._fm_cache) >= _FM_CACHE_LIMIT:
+                self._fm_cache.clear()
             return self._fm_cache.setdefault(fid, QFontMetrics(font))
 
     def fontmetrics_f(self, font):
         fid = font_key_cached(font)
         try:
             return self._fm_cache_f[fid]
         except KeyError:
+            if len(self._fm_cache_f) >= _FM_CACHE_LIMIT:
+                self._fm_cache_f.clear()
             return self._fm_cache_f.setdefault(fid, QFontMetricsF(font))
 
     def heightForWidth(self, font, flags, text, width):
@@ -359,6 +364,8 @@ def effectiveAscent(self, font):
         ascent = ASCENTCACHE.get(fontKey)
         if ascent is not None:
             return ascent
+        if len(ASCENTCACHE) >= _FM_CACHE_LIMIT:
+            ASCENTCACHE.clear()
         return ASCENTCACHE.setdefault(fontKey, self.findAscent(font))
 
     def findAscent(self, font):
@@ -411,6 +418,8 @@ def textMargins(self, font):
         if cached is None:
             fm = self.fontmetrics(font)
             cached = (0, 0, fm.ascent() - self.effectiveAscent(font), fm.descent())
+            if len(self._margins_cache) >= _FM_CACHE_LIMIT:
+                self._margins_cache.clear()
             self._margins_cache[fkey] = cached
         self._margins_last_id = font_id
         self._margins_last_value = cached