forgot to add the BLEEDING FILE

fileLock.py

@@ -0,0 +1,104 @@
+# Copyright (c) 2009, Evan Fosmark
+# All rights reserved.
+# 
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met: 
+# 
+# 1. Redistributions of source code must retain the above copyright notice, this
+#    list of conditions and the following disclaimer. 
+# 2. 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. 
+# 
+# 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 THE COPYRIGHT OWNER OR CONTRIBUTORS 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.
+# 
+# The views and conclusions contained in the software and documentation are those
+# of the authors and should not be interpreted as representing official policies, 
+# either expressed or implied, of the FreeBSD Project.
+
+import os
+import time
+import errno
+
+class FileLockException(Exception):
+    pass
+
+class FileLock(object):
+    """ A file locking mechanism that has context-manager support so 
+        you can use it in a with statement. This should be relatively cross
+        compatible as it doesn't rely on msvcrt or fcntl for the locking.
+    """
+
+    def __init__(self, file_name, timeout=10, delay=.05):
+        """ Prepare the file locker. Specify the file to lock and optionally
+            the maximum timeout and the delay between each attempt to lock.
+        """
+        self.is_locked = False
+        self.lockfile = os.path.join(os.getcwd(), "%s.lock" % file_name)
+        self.file_name = file_name
+        self.timeout = timeout
+        self.delay = delay
+
+
+    def acquire(self):
+        """ Acquire the lock, if possible. If the lock is in use, it check again
+            every `wait` seconds. It does this until it either gets the lock or
+            exceeds `timeout` number of seconds, in which case it throws 
+            an exception.
+        """
+        start_time = time.time()
+        while True:
+            try:
+                self.fd = os.open(self.lockfile, os.O_CREAT|os.O_EXCL|os.O_RDWR)
+                break;
+            except OSError as e:
+                if e.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):
+        """ Get rid of the lock by deleting the lockfile. 
+            When working in a `with` statement, this gets automatically 
+            called at the end.
+        """
+        if self.is_locked:
+            os.close(self.fd)
+            os.unlink(self.lockfile)
+            self.is_locked = False
+
+
+    def __enter__(self):
+        """ Activated when used in the with statement. 
+            Should automatically acquire a lock to be used in the with block.
+        """
+        if not self.is_locked:
+            self.acquire()
+        return self
+
+
+    def __exit__(self, type, value, traceback):
+        """ Activated at the end of the with statement.
+            It automatically releases the lock if it isn't locked.
+        """
+        if self.is_locked:
+            self.release()
+
+
+    def __del__(self):
+        """ Make sure that the FileLock instance doesn't leave a lockfile
+            lying around.
+        """
+        self.release()