Integrate persistent cache with "var_dir" conf option

[mpd-sima.git] / sima / utils / filelock.py

diff --git a/sima/utils/filelock.py b/sima/utils/filelock.py
new file mode 100644 (file)
index 0000000..8f7065f
--- /dev/null
+++ b/sima/utils/filelock.py
@@ -0,0 +1,95 @@
+# -*- coding: utf-8 -*-
+
+# Copyright (c) 2009 Evan Fosmark
+# Copyright (c) 2014 Jack Kaliko <kaliko@azylum.org>
+#
+#   This program 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.
+#
+#   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+#
+
+# https://github.com/dmfrey/FileLock
+"""
+Plain file lock to une in context:
+    >>> with FileLock('/path/to/file/to/write'):
+    >>>     # a lock file is maintain within the scope of this context:
+    >>>     # /path/to/file/to/write.lock
+    >>>     ... # process file writing
+"""
+
+import errno
+import os
+import time
+
+class FileLockException(Exception):
+    """FileLock Exception"""
+    pass
+
+class FileLock:
+    """ A plain file lock whit context-manager"""
+
+    def __init__(self, file_name, timeout=10, delay=.05):
+        """
+        Setup file lock.
+        Setup timeout and the delay.
+        """
+        self.filedsc = None
+        self.is_locked = False
+        dirname = os.path.dirname(file_name)
+        self.lockfile = os.path.join(dirname, '{0}.lock'.format(file_name))
+        self.file_name = file_name
+        self.timeout = timeout
+        self.delay = delay
+
+    def acquire(self):
+        """Acquire the lock, if possible.
+        """
+        start_time = time.time()
+        while True:
+            try:
+                self.filedsc = os.open(self.lockfile,
+                                       os.O_CREAT|os.O_EXCL|os.O_RDWR)
+                break
+            except OSError as err:
+                if err.errno != errno.EEXIST:
+                    raise
+                if (time.time() - start_time) >= self.timeout:
+                    raise FileLockException('Timeout occured.')
+                time.sleep(self.delay)
+        self.is_locked = True
+
+    def release(self):
+        """Release the lock.
+        """
+        if self.is_locked:
+            os.close(self.filedsc)
+            os.unlink(self.lockfile)
+            self.is_locked = False
+
+    def __enter__(self):
+        """start of the with statement.
+        """
+        if not self.is_locked:
+            self.acquire()
+        return self
+
+    def __exit__(self, type, value, traceback):
+        """end of the with statement
+        """
+        if self.is_locked:
+            self.release()
+
+    def __del__(self):
+        """Cleanup
+        """
+        self.release()