Move locking of fontlist.json *into* json_dump.

anntzer · anntzer · commit e1ccb6f85100 · 2020-01-05T21:35:39.000+01:00
This makes it easier for end users to call json_dump (which is public
API) safely, given that _lock_path is not public API.
diff --git a/doc/api/next_api_changes/behaviour.rst b/doc/api/next_api_changes/behaviour.rst
@@ -62,3 +62,7 @@ property.  This now raises a TypeError.
 `.FileMovieWriter` now defaults to writing temporary frames in a temporary
 directory, which is always cleared at exit.  In order to keep the individual
 frames saved on the filesystem, pass an explicit *frame_prefix*.
+
+`.font_manager.json_dump` now locks the font manager dump file
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... to prevent multiple processes from writing to it at the same time.
diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
@@ -914,11 +914,14 @@ def json_dump(data, filename):
     shipped with Matplotlib) are stored relative to that data path (to remain
     valid across virtualenvs).
 
+    This function temporarily locks the output file to prevent multiple
+    processes from overwriting one another's output.
+
     See Also
     --------
     json_load
     """
-    with open(filename, 'w') as fh:
+    with cbook._lock_path(filename), open(filename, 'w') as fh:
         try:
             json.dump(data, fh, cls=_JSONEncoder, indent=2)
         except OSError as e:
@@ -1335,8 +1338,7 @@ def get_font(filename, hinting_factor=None):
 def _rebuild():
     global fontManager
     fontManager = FontManager()
-    with cbook._lock_path(_fmcache):
-        json_dump(fontManager, _fmcache)
+    json_dump(fontManager, _fmcache)
     _log.info("generated new fontManager")
 
 
