from __future__ import absolute_import import time import os from . import (LockBase, LockFailed, NotLocked, NotMyLock, LockTimeout, AlreadyLocked) class LinkLockFile(LockBase): """Lock access to a file using atomic property of link(2). >>> lock = LinkLockFile('somefile') >>> lock = LinkLockFile('somefile', threaded=False) """ def acquire(self, timeout=None): try: open(self.unique_name, "wb").close() except IOError: raise LockFailed("failed to create %s" % self.unique_name) timeout = timeout if timeout is not None else self.timeout end_time = time.time() if timeout is not None and timeout > 0: end_time += timeout while True: # Try and create a hard link to it. try: os.link(self.unique_name, self.lock_file) except OSError: # Link creation failed. Maybe we've double-locked? nlinks = os.stat(self.unique_name).st_nlink if nlinks == 2: # The original link plus the one I created == 2. We're # good to go. return else: # Otherwise the lock creation failed. if timeout is not None and time.time() > end_time: os.unlink(self.unique_name) if timeout > 0: raise LockTimeout("Timeout waiting to acquire" " lock for %s" % self.path) else: raise AlreadyLocked("%s is already locked" % self.path) time.sleep(timeout is not None and timeout / 10 or 0.1) else: # Link creation succeeded. We're good to go. return def release(self): if not self.is_locked(): raise NotLocked("%s is not locked" % self.path) elif not os.path.exists(self.unique_name): raise NotMyLock("%s is locked, but not by me" % self.path) os.unlink(self.unique_name) os.unlink(self.lock_file) def is_locked(self): return os.path.exists(self.lock_file) def i_am_locking(self): return (self.is_locked() and os.path.exists(self.unique_name) and os.stat(self.unique_name).st_nlink == 2) def break_lock(self): if os.path.exists(self.lock_file): os.unlink(self.lock_file)