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