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1 # lock.py - simple locking scheme for mercurial
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2 #
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3 # Copyright 2005 Matt Mackall <mpm@selenic.com>
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4 #
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5 # This software may be used and distributed according to the terms
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6 # of the GNU General Public License, incorporated herein by reference.
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7
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8 import os, time
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9
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10 class LockHeld(Exception):
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11 pass
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12
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13 class lock:
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14 def __init__(self, file, wait = 1):
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15 self.f = file
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16 self.held = 0
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17 self.wait = wait
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18 self.lock()
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19
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20 def __del__(self):
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21 self.release()
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22
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23 def lock(self):
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24 while 1:
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25 try:
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26 self.trylock()
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27 return 1
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28 except LockHeld, inst:
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29 if self.wait:
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30 time.sleep(1)
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31 continue
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32 raise inst
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33
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34 def trylock(self):
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35 pid = os.getpid()
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36 try:
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37 os.symlink(str(pid), self.f)
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38 self.held = 1
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39 except:
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40 raise LockHeld(os.readlink(self.f))
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41
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42 def release(self):
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43 if self.held:
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44 self.held = 0
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45 os.unlink(self.f)
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46
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