| 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) |