FontManager fixes.

anntzer · anntzer · commit a0065c30ae7a · 2020-06-23T09:04:54.000+02:00
Previously, when using findfont with rebuild_is_missing (the default)
_rebuild() would generate a new fontManager instance, but because
findfont is defined as `findfont = fontManager.findfont`, this would
keep using the old fontManager instance; we can't just fix this with
`def findfont(...): return fontManager.findfont(...)` because people may
be importing the fontManager instance anyways and not benefitting from
the rebuilt one.

Instead, overwrite(!) the contents of the existing fontManager instance
with the new one as needed.
diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
@@ -1371,8 +1371,13 @@ def _findfont_cached(self, prop, fontext, directory, fallback_to_default,
             if rebuild_if_missing:
                 _log.info(
                     'findfont: Found a missing font file.  Rebuilding cache.')
-                _rebuild()
-                return fontManager.findfont(
+                new_fm = _load_fontmanager(try_read_cache=False)
+                # Replace self by the new fontmanager, because users may have
+                # a reference to this specific instance.
+                # TODO: _load_fontmanager should really be (used by) a method
+                # modifying the instance in place.
+                vars(self).update(vars(new_fm))
+                return self.findfont(
                     prop, fontext, directory, rebuild_if_missing=False)
             else:
                 raise ValueError("No valid font could be found")
@@ -1394,11 +1399,6 @@ def is_opentype_cff_font(filename):
         return False
 
 
-_fmcache = os.path.join(
-    mpl.get_cachedir(), 'fontlist-v{}.json'.format(FontManager.__version__))
-fontManager = None
-
-
 _get_font = lru_cache(64)(ft2font.FT2Font)
 # FT2Font objects cannot be used across fork()s because they reference the same
 # FT_Library object.  While invalidating *all* existing FT2Fonts after a fork
@@ -1418,22 +1418,23 @@ def get_font(filename, hinting_factor=None):
                      _kerning_factor=rcParams['text.kerning_factor'])
 
 
-def _rebuild():
-    global fontManager
-    _log.info("Generating new fontManager, this may take some time...")
-    fontManager = FontManager()
-    json_dump(fontManager, _fmcache)
-
-
-try:
-    fontManager = json_load(_fmcache)
-except Exception:
-    _rebuild()
-else:
-    if getattr(fontManager, '_version', object()) != FontManager.__version__:
-        _rebuild()
-    else:
-        _log.debug("Using fontManager instance from %s", _fmcache)
+def _load_fontmanager(*, try_read_cache=True):
+    fm_path = Path(
+        mpl.get_cachedir(), f"fontlist-v{FontManager.__version__}.json")
+    if try_read_cache:
+        try:
+            fm = json_load(fm_path)
+        except Exception as exc:
+            pass
+        else:
+            if getattr(fm, "_version", object()) == FontManager.__version__:
+                _log.debug("Using fontManager instance from %s", fm_path)
+                return fm
+    fm = FontManager()
+    json_dump(fm, fm_path)
+    _log.info("generated new fontManager")
+    return fm
 
 
+fontManager = _load_fontmanager()
 findfont = fontManager.findfont
