From 9d3ded841d4def41a5a61dd18e2e69b819025dc0 Mon Sep 17 00:00:00 2001
From: Pierre-Yves Chibon <pingou@pingoured.fr>
Date: Oct 26 2015 10:04:07 +0000
Subject: Embed and adjust for our need the simpleflock module


---

diff --git a/mdapi/file_lock.py b/mdapi/file_lock.py
new file mode 100644
index 0000000..9fdb867
--- /dev/null
+++ b/mdapi/file_lock.py
@@ -0,0 +1,64 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright © derpston.
+#
+# Source: https://github.com/derpston/python-simpleflock/
+#
+# License: WTFPL
+#
+
+'''
+Simple file lock mechanism
+'''
+
+import time
+import os
+import fcntl
+import errno
+
+
+class FileFlock:
+    """ Provides the simplest possible interface to flock-based file locking.
+    Intended for use with the `with` syntax. It will create/truncate/delete
+    the lock file as necessary.
+
+    """
+
+    def __init__(self, path, timeout=None, wait_for=0.1):
+        self._path = path
+        self._timeout = timeout
+        self._fd = None
+        self.wait_for = wait_for
+
+    def __enter__(self):
+        self._fd = os.open(self._path, os.O_CREAT)
+        start_lock_search = time.time()
+        while True:
+            try:
+                fcntl.flock(self._fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+                # Lock acquired!
+                return
+            except IOError as ex:
+                # Keep going if resource temporarily unavailable
+                if ex.errno != errno.EAGAIN:
+                    raise
+                # Exceeded the user-specified timeout.
+                elif self._timeout is not None \
+                        and time.time() > (start_lock_search + self._timeout):
+                    raise
+
+            # Let's not spin continuously
+            time.sleep(self.wait_for)
+
+    def __exit__(self, *args):
+        fcntl.flock(self._fd, fcntl.LOCK_UN)
+        os.close(self._fd)
+        self._fd = None
+
+        # Try to remove the lock file, but don't try too hard because it is
+        # unnecessary. This is mostly to help the user see whether a lock
+        # exists by examining the filesystem.
+        try:
+            os.unlink(self._path)
+        except:
+            pass