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annotate mercurial/transaction.py @ 95:589f507bb259

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Beginnings of transaction undo support
author mpm@selenic.com
date Wed, 18 May 2005 16:31:51 -0800
parents 42177b56b949
children 8d55c2d72c7c
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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, after = None):
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18 self.opener = opener
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19 self.after = after
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20 self.entries = []
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21 self.map = {}
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22 self.journal = journal
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23
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24 # abort here if the journal already exists
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25 if os.path.exists(self.journal):
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26 raise "journal already exists!"
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28 self.file = open(self.journal, "w")
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30 def __del__(self):
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31 if self.entries: self.abort()
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32 try: os.unlink(self.journal)
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33 except: pass
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34
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35 def add(self, file, offset):
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36 if file in self.map: return
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37 self.entries.append((file, offset))
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38 self.map[file] = 1
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39 # add enough data to the journal to do the truncate
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40 self.file.write("%s\0%d\n" % (file, offset))
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41 self.file.flush()
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42
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43 def close(self):
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44 self.file.close()
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45 self.entries = []
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46 if self.after:
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47 os.rename(self.journal, self.after)
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48 else:
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49 os.unlink(self.journal)
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51 def abort(self):
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52 if not self.entries: return
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53
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54 print "transaction abort!"
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55
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56 for f, o in self.entries:
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57 self.opener(f, "a").truncate(o)
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58
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59 self.entries = []
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60
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61 print "rollback completed"
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63 def recover(self):
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64 for l in open(self.journal).readlines():
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65 f, o = l.split('\0')
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66 self.opener(f, "a").truncate(int(o))
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67 os.unlink(self.journal)
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