Add file locking for -j parallel execution.

cdist/flock.py

@@ -0,0 +1,58 @@
+# -*- coding: utf-8 -*-
+#
+# 2017 Darko Poljak (darko.poljak at gmail.com)
+#
+# This file is part of cdist.
+#
+# cdist is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# cdist 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with cdist. If not, see <http://www.gnu.org/licenses/>.
+#
+#
+
+import fcntl
+import logging
+import os
+
+
+log = logging.getLogger('cdist-flock')
+
+
+class Flock():
+    def __init__(self, path):
+        self.path = path
+        self.lockfd = None
+
+    def flock(self):
+        log.debug('Acquiring lock on %s', self.path)
+        self.lockfd = open(self.path, 'w+')
+        fcntl.flock(self.lockfd, fcntl.LOCK_EX)
+        log.debug('Acquired lock on %s', self.path)
+
+    def funlock(self):
+        log.debug('Releasing lock on %s', self.path)
+        fcntl.flock(self.lockfd, fcntl.LOCK_UN)
+        self.lockfd.close()
+        self.lockfd = None
+        try:
+            os.remove(self.path)
+        except FileNotFoundError:
+            pass
+        log.debug('Released lock on %s', self.path)
+
+    def __enter__(self):
+        self.flock()
+        return self
+
+    def __exit__(self, *args):
+        self.funlock()
+        return False