author | mpm@selenic.com |
Tue, 10 May 2005 00:32:05 -0800 | |
changeset 43 | 42177b56b949 |
parent 42 | 91f1fa847158 |
child 95 | 589f507bb259 |
permissions | -rw-r--r-- |
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# transaction.py - simple journalling scheme for mercurial |
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# |
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# This transaction scheme is intended to gracefully handle program |
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# errors and interruptions. More serious failures like system crashes |
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# can be recovered with an fsck-like tool. As the whole repository is |
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# effectively log-structured, this should amount to simply truncating |
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# anything that isn't referenced in the changelog. |
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# |
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# Copyright 2005 Matt Mackall <mpm@selenic.com> |
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# |
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# This software may be used and distributed according to the terms |
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# of the GNU General Public License, incorporated herein by reference. |
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import os |
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class transaction: |
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def __init__(self, opener, journal): |
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self.opener = opener |
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self.entries = [] |
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self.map = {} |
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self.journal = journal |
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# abort here if the journal already exists |
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if os.path.exists(self.journal): |
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print "journal already exists, recovering" |
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self.recover() |
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self.file = open(self.journal, "w") |
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def __del__(self): |
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if self.entries: self.abort() |
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try: os.unlink(self.journal) |
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except: pass |
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def add(self, file, offset): |
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if file in self.map: return |
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self.entries.append((file, offset)) |
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self.map[file] = 1 |
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# add enough data to the journal to do the truncate |
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self.file.write("%s\0%d\n" % (file, offset)) |
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self.file.flush() |
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def close(self): |
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self.file.close() |
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self.entries = [] |
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os.unlink(self.journal) |
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def abort(self): |
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if not self.entries: return |
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print "transaction abort!" |
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for f, o in self.entries: |
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self.opener(f, "a").truncate(o) |
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self.entries = [] |
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print "rollback completed" |
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def recover(self): |
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for l in open(self.journal).readlines(): |
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f, o = l.split('\0') |
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self.opener(f, "a").truncate(int(o)) |
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os.unlink(self.journal) |
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