X-Git-Url: https://git.kaliko.me/?a=blobdiff_plain;f=sima%2Flib%2Fhttpcli%2Ffilelock.py;fp=sima%2Flib%2Fhttpcli%2Ffilelock.py;h=6dc331be75a3828d080bf1a543ce230c15d202d5;hb=bed2018b162e3493dd5a5a7fe5433af2005a7d0a;hp=0000000000000000000000000000000000000000;hpb=3ee55407f08ca20a37ca008822283682d2ba58f9;p=mpd-sima.git

diff --git a/sima/lib/httpcli/filelock.py b/sima/lib/httpcli/filelock.py
new file mode 100644
index 0000000..6dc331b
--- /dev/null
+++ b/sima/lib/httpcli/filelock.py
@@ -0,0 +1,80 @@
+# -*- coding: utf-8 -*-
+# https://github.com/dmfrey/FileLock
+
+import os
+import time
+import errno
+
+class FileLockException(Exception):
+    pass
+
+class FileLock:
+    """ 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()