Move locking of fontlist.json *into* json_dump.

anntzer · anntzer · commit bf869e7759a5 · 2020-01-14T01:37:47.000+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
@@ -70,3 +70,7 @@ shape ``(n, 2)`` would plot the first column of *x* against the first column
 of *y*, the second column of *x* against the second column of *y*, **and** the
 first column of *x* against the third column of *y*.  This now raises an error
 instead.
+
+`.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
@@ -911,11 +911,14 @@ 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")
 
 
