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annotate web/atomicfile.py @ 222:fb742ee61342

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screenshot of parameter UI
author Matt Johnston <matt@ucc.asn.au>
date Fri, 19 Dec 2014 22:50:37 +0800
parents 6dd157a12035
children 87c20b8c5472
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1 import os
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2 import time
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3 import fcntl
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4 import sys
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5
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6 class AtomicFile(object):
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7 DELAY = 0.5
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8 def __init__(self, name):
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9 self.name = name
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10
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11 def write(self, data, timeout = 5):
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12 try:
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13 end = time.time() + timeout
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14 with open(self.name, "r+") as f:
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15 while timeout == 0 or time.time() < end:
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16 try:
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17 fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
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18 except IOError:
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19 time.sleep(DELAY)
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20 continue
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21
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22 os.ftruncate(f.fileno(), 0)
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23 f.write(data)
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24 return True
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25
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26 except IOError, e:
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27 print>>sys.stderr, e
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28
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29 return False
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30
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31 def read(self, timeout = 5):
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32 try:
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33 end = time.time() + timeout
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34 with open(self.name, "r") as f:
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35 while timeout == 0 or time.time() < end:
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36 try:
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37 fcntl.lockf(f, fcntl.LOCK_SH | fcntl.LOCK_NB)
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38 except IOError:
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39 time.sleep(DELAY)
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40 continue
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41
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42 return f.read()
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43
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44 except IOError, e:
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45 print>>sys.stderr, e
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46
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47 return None