71 lines
2.6 KiB
Python
71 lines
2.6 KiB
Python
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from __future__ import absolute_import
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import os
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import time
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from . import (LockBase, NotLocked, NotMyLock, LockTimeout,
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AlreadyLocked)
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class SymlinkLockFile(LockBase):
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"""Lock access to a file using symlink(2)."""
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def __init__(self, path, threaded=True, timeout=None):
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# super(SymlinkLockFile).__init(...)
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LockBase.__init__(self, path, threaded, timeout)
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# split it back!
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self.unique_name = os.path.split(self.unique_name)[1]
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def acquire(self, timeout=None):
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# Hopefully unnecessary for symlink.
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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 symbolic link to it.
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try:
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os.symlink(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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if self.i_am_locking():
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# Linked to out unique name. Proceed.
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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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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 / 10 if timeout is not None else 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 self.i_am_locking():
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raise NotMyLock("%s is locked, but not by me" % self.path)
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os.unlink(self.lock_file)
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def is_locked(self):
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return os.path.islink(self.lock_file)
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def i_am_locking(self):
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return (os.path.islink(self.lock_file)
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and os.readlink(self.lock_file) == self.unique_name)
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def break_lock(self):
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if os.path.islink(self.lock_file): # exists && link
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os.unlink(self.lock_file)
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