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1 from __future__ import absolute_import
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2
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3 import time
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4 import os
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5
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6 from . import (LockBase, LockFailed, NotLocked, NotMyLock, LockTimeout,
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7 AlreadyLocked)
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8
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9 class SymlinkLockFile(LockBase):
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10 """Lock access to a file using symlink(2)."""
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11
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12 def __init__(self, path, threaded=True, timeout=None):
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13 # super(SymlinkLockFile).__init(...)
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14 LockBase.__init__(self, path, threaded, timeout)
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15 # split it back!
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16 self.unique_name = os.path.split(self.unique_name)[1]
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17
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18 def acquire(self, timeout=None):
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19 # Hopefully unnecessary for symlink.
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20 #try:
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21 # open(self.unique_name, "wb").close()
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22 #except IOError:
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23 # raise LockFailed("failed to create %s" % self.unique_name)
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24 timeout = timeout is not None and timeout or self.timeout
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25 end_time = time.time()
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26 if timeout is not None and timeout > 0:
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27 end_time += timeout
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28
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29 while True:
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30 # Try and create a symbolic link to it.
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31 try:
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32 os.symlink(self.unique_name, self.lock_file)
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33 except OSError:
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34 # Link creation failed. Maybe we've double-locked?
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35 if self.i_am_locking():
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36 # Linked to out unique name. Proceed.
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37 return
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38 else:
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39 # Otherwise the lock creation failed.
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40 if timeout is not None and time.time() > end_time:
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41 if timeout > 0:
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42 raise LockTimeout("Timeout waiting to acquire"
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43 " lock for %s" %
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44 self.path)
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45 else:
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46 raise AlreadyLocked("%s is already locked" %
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47 self.path)
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48 time.sleep(timeout/10 if timeout is not None else 0.1)
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49 else:
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50 # Link creation succeeded. We're good to go.
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51 return
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52
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53 def release(self):
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54 if not self.is_locked():
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55 raise NotLocked("%s is not locked" % self.path)
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56 elif not self.i_am_locking():
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57 raise NotMyLock("%s is locked, but not by me" % self.path)
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58 os.unlink(self.lock_file)
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59
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60 def is_locked(self):
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61 return os.path.islink(self.lock_file)
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62
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63 def i_am_locking(self):
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64 return os.path.islink(self.lock_file) and \
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65 os.readlink(self.lock_file) == self.unique_name
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66
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67 def break_lock(self):
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68 if os.path.islink(self.lock_file): # exists && link
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69 os.unlink(self.lock_file)
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