Move locking of fontlist.json *into* json_dump.

anntzer · anntzer · commit ae891aed9191 · 2020-03-02T22:18:13.000+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
@@ -100,4 +100,8 @@ deprecation warning.
 
 Previously setting the *ecolor* would turn off automatic color cycling for the plot, leading to the 
 the lines and markers defaulting to whatever the first color in the color cycle was in the case of 
-multiple plot calls. 
+multiple plot calls. 
+
+`.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:
@@ -1338,8 +1341,7 @@ def _rebuild():
     global fontManager
     _log.info("Generating new fontManager, this may take some time...")
     fontManager = FontManager()
-    with cbook._lock_path(_fmcache):
-        json_dump(fontManager, _fmcache)
+    json_dump(fontManager, _fmcache)
 
 
 try:
