mercurial/transaction.py
author mpm@selenic.com
Sun, 22 May 2005 08:13:38 -0800
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child 162 5dcbe4d9a30c
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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, after = None):
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        self.opener = opener
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        self.after = after
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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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            raise "journal already exists!"
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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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        if self.after:
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            os.rename(self.journal, self.after)
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        else:
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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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            try:
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                self.opener(f, "a").truncate(o)
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            except:
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                print "failed to truncate", f
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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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