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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 LinkLockFile(LockBase):
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10 """Lock access to a file using atomic property of link(2).
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11
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12 >>> lock = LinkLockFile('somefile')
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13 >>> lock = LinkLockFile('somefile', threaded=False)
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14 """
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15
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16 def acquire(self, timeout=None):
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17 try:
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18 open(self.unique_name, "wb").close()
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19 except IOError:
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20 raise LockFailed("failed to create %s" % self.unique_name)
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21
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22 timeout = timeout is not None and timeout or self.timeout
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23 end_time = time.time()
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24 if timeout is not None and timeout > 0:
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25 end_time += timeout
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26
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27 while True:
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28 # Try and create a hard link to it.
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29 try:
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30 os.link(self.unique_name, self.lock_file)
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31 except OSError:
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32 # Link creation failed. Maybe we've double-locked?
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33 nlinks = os.stat(self.unique_name).st_nlink
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34 if nlinks == 2:
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35 # The original link plus the one I created == 2. We're
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36 # good to go.
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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 os.unlink(self.unique_name)
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42 if timeout > 0:
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43 raise LockTimeout("Timeout waiting to acquire"
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44 " lock for %s" %
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45 self.path)
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46 else:
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47 raise AlreadyLocked("%s is already locked" %
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48 self.path)
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49 time.sleep(timeout is not None and timeout/10 or 0.1)
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50 else:
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51 # Link creation succeeded. We're good to go.
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52 return
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53
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54 def release(self):
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55 if not self.is_locked():
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56 raise NotLocked("%s is not locked" % self.path)
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57 elif not os.path.exists(self.unique_name):
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58 raise NotMyLock("%s is locked, but not by me" % self.path)
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59 os.unlink(self.unique_name)
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60 os.unlink(self.lock_file)
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61
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62 def is_locked(self):
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63 return os.path.exists(self.lock_file)
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64
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65 def i_am_locking(self):
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66 return (self.is_locked() and
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67 os.path.exists(self.unique_name) and
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68 os.stat(self.unique_name).st_nlink == 2)
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69
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70 def break_lock(self):
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71 if os.path.exists(self.lock_file):
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72 os.unlink(self.lock_file)
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73
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