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1 # transaction.py - simple journalling scheme for mercurial |
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2 # |
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3 # This transaction scheme is intended to gracefully handle program |
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4 # errors and interruptions. More serious failures like system crashes |
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5 # can be recovered with an fsck-like tool. As the whole repository is |
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6 # effectively log-structured, this should amount to simply truncating |
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7 # anything that isn't referenced in the changelog. |
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8 # |
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9 # Copyright 2005 Matt Mackall <mpm@selenic.com> |
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10 # |
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11 # This software may be used and distributed according to the terms |
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12 # of the GNU General Public License, incorporated herein by reference. |
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13 |
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14 import os |
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15 |
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16 class transaction: |
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17 def __init__(self, opener, journal): |
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18 self.opener = opener |
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19 self.entries = [] |
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20 self.journal = journal |
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21 |
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22 # abort here if the journal already exists |
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23 if os.path.exists(self.journal): |
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24 raise "Journal already exists!" |
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25 self.file = open(self.journal, "w") |
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26 |
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27 def __del__(self): |
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28 if self.entries: self.abort() |
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29 |
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30 def add(self, file, offset): |
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31 self.entries.append((file, offset)) |
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32 # add enough data to the journal to do the truncate |
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33 self.file.write("%s\0%d\n" % (file, offset)) |
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34 self.file.flush() |
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35 |
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36 def close(self): |
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37 self.file.close() |
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38 self.entries = [] |
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39 os.unlink(self.journal) |
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40 |
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41 def abort(self): |
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42 if not self.entries: return |
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43 |
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44 print "transaction abort!" |
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45 |
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46 for f, o in self.entries: |
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47 self.opener(f, "a").truncate(o) |
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48 |
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49 self.entries = [] |
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50 |
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51 try: |
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52 os.unlink(self.journal) |
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53 self.file.close() |
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54 except: pass |
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55 |
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56 print "rollback completed" |
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57 |
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58 def recover(self): |
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59 for l in open(self.journal).readlines(): |
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60 f, o = l.split('\0') |
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61 self.opener(f, "a").truncate(int(o)) |
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62 |