Use a lock directory to prevent race condition

...when creating the font cache
matplotlib · jenshnielsen · Oct 27, 2015 · Oct 19, 2015 · Oct 27, 2015 · Oct 27, 2015
commit c3d6a761f92c39bab8fa9729eeadfad5d0cb1a11
diff --git a/LICENSE/LICENSE_CONDA b/LICENSE/LICENSE_CONDA
@@ -0,0 +1,51 @@
+Except where noted below, conda is released under the following terms:
+
+(c) 2012 Continuum Analytics, Inc. / http://continuum.io
+All Rights Reserved
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in the
+      documentation and/or other materials provided with the distribution.
+    * Neither the name of Continuum Analytics, Inc. nor the
+      names of its contributors may be used to endorse or promote products
+      derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL CONTINUUM ANALYTICS BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+Exceptions
+==========
+
+versioneer.py is Public Domain
+
+The ProgressBar package is released under the following terms:
+
+# progressbar  - Text progress bar library for Python.
+# Copyright (c) 2005 Nilton Volpato
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
diff --git a/lib/matplotlib/cbook.py b/lib/matplotlib/cbook.py
@@ -2550,3 +2550,54 @@ def get_label(y, default_name):
 else:
    def _putmask(a, mask, values):
        return np.copyto(a, values, where=mask)
+
+
+class Locked(object):
+    """
+    Context manager to handle locks.
+
+    Based on code from conda.
+
+    (c) 2012-2013 Continuum Analytics, Inc. / http://continuum.io
+    All Rights Reserved
+
+    conda is distributed under the terms of the BSD 3-clause license.
+    Consult LICENSE.txt or http://opensource.org/licenses/BSD-3-Clause.
+    """
+    def __init__(self, path):
+        LOCKFN = '.matplotlib_lock'
+        self.path = path
+        self.end = "-" + str(os.getpid())
+        self.lock_path = os.path.join(self.path, LOCKFN + self.end)
+        self.pattern = os.path.join(self.path, LOCKFN + '-*')
+        self.remove = True
+
+    def __enter__(self):
+        retries = 10
+        sleeptime = 1
+        while retries:
+            files = glob.glob(self.pattern)
+            if files and not files[0].endswith(self.end):
+                time.sleep(sleeptime)
+                sleeptime *= 2
+                retries -= 1
+            else:
+                break
+        else:
+            raise RuntimeError(lockstr)
+
+        if not files:
+            try:
+                os.makedirs(self.lock_path)
+            except OSError:
+                pass
+        else:  # PID lock already here --- someone else will remove it.
+            self.remove = False
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        if self.remove:
+            for path in self.lock_path, self.path:
+                try:
+                    os.rmdir(path)
+                except OSError:
+                    pass
diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
@@ -1405,10 +1405,9 @@ def findfont(prop, fontext='ttf'):
 else:
    _fmcache = None

-    if not 'TRAVIS' in os.environ:
-        cachedir = get_cachedir()
-        if cachedir is not None:
-            _fmcache = os.path.join(cachedir, 'fontList.json')
+    cachedir = get_cachedir()
+    if cachedir is not None:
+        _fmcache = os.path.join(cachedir, 'fontList.json')

    fontManager = None

@@ -1419,9 +1418,13 @@ def findfont(prop, fontext='ttf'):

    def _rebuild():
        global fontManager
+
        fontManager = FontManager()
+
        if _fmcache:
-            json_dump(fontManager, _fmcache)
+            with cbook.Locked(cachedir):
+                json_dump(fontManager, _fmcache)
+
        verbose.report("generated new fontManager")

    if _fmcache: