transaction: add support for non-append files

This adds support for normal, non-append-only files in transactions.  For
example, .hg/store/fncache and .hg/store/phaseroots should be written as part of
the transaction, but are not append only files.

This adds a journal.backupfiles along side the normal journal. This tracks which
files have been backed up as part of the transaction.  transaction.addbackup()
creates a backup of the file (using a hardlink), which is later used to recover
in the event of the transaction failing.

Using a seperate journal allows the repository to still be used by older
versions of Mercurial. A future patch will use this functionality and add tests
for it.

mercurial/transaction.py

@@ -1,204 +1,303 b''
 # transaction.py - simple journaling scheme for mercurial
 #
 # This transaction scheme is intended to gracefully handle program
 # errors and interruptions. More serious failures like system crashes
 # can be recovered with an fsck-like tool. As the whole repository is
 # effectively log-structured, this should amount to simply truncating
 # anything that isn't referenced in the changelog.
 #
 # Copyright 2005, 2006 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
-import errno
-import error
+import errno, os
+import error, util
 
 def active(func):
     def _active(self, *args, **kwds):
         if self.count == 0:
             raise error.Abort(_(
                 'cannot use transaction when it is already committed/aborted'))
         return func(self, *args, **kwds)
     return _active
 
-def _playback(journal, report, opener, entries, unlink=True):
+def _playback(journal, report, opener, entries, backupentries, unlink=True):
     for f, o, ignore in entries:
         if o or not unlink:
             try:
                 fp = opener(f, 'a')
                 fp.truncate(o)
                 fp.close()
             except IOError:
                 report(_("failed to truncate %s\n") % f)
                 raise
         else:
             try:
                 opener.unlink(f)
             except (IOError, OSError), inst:
                 if inst.errno != errno.ENOENT:
                     raise
+
+    backupfiles = []
+    for f, b, ignore in backupentries:
+        filepath = opener.join(f)
+        backuppath = opener.join(b)
+        try:
+            util.copyfile(backuppath, filepath)
+            backupfiles.append(b)
+        except IOError:
+            report(_("failed to recover %s\n") % f)
+            raise
+
     opener.unlink(journal)
+    backuppath = "%s.backupfiles" % journal
+    if opener.exists(backuppath):
+        opener.unlink(backuppath)
+    for f in backupfiles:
+        opener.unlink(f)
 
 class transaction(object):
     def __init__(self, report, opener, journal, after=None, createmode=None,
             onclose=None, onabort=None):
         """Begin a new transaction
 
         Begins a new transaction that allows rolling back writes in the event of
         an exception.
 
         * `after`: called after the transaction has been committed
         * `createmode`: the mode of the journal file that will be created
         * `onclose`: called as the transaction is closing, but before it is
         closed
         * `onabort`: called as the transaction is aborting, but before any files
         have been truncated
         """
         self.count = 1
         self.usages = 1
         self.report = report
         self.opener = opener
         self.after = after
         self.onclose = onclose
         self.onabort = onabort
         self.entries = []
+        self.backupentries = []
         self.map = {}
+        self.backupmap = {}
         self.journal = journal
         self._queue = []
 
+        self.backupjournal = "%s.backupfiles" % journal
         self.file = opener.open(self.journal, "w")
+        self.backupsfile = opener.open(self.backupjournal, 'w')
         if createmode is not None:
             opener.chmod(self.journal, createmode & 0666)
+            opener.chmod(self.backupjournal, createmode & 0666)
 
     def __del__(self):
         if self.journal:
             self._abort()
 
     @active
     def startgroup(self):
-        self._queue.append([])
+        self._queue.append(([], []))
 
     @active
     def endgroup(self):
         q = self._queue.pop()
-        d = ''.join(['%s\0%d\n' % (x[0], x[1]) for x in q])
-        self.entries.extend(q)
+        self.entries.extend(q[0])
+        self.backupentries.extend(q[1])
+
+        offsets = []
+        backups = []
+        for f, o, _ in q[0]:
+            offsets.append((f, o))
+
+        for f, b, _ in q[1]:
+            backups.append((f, b))
+
+        d = ''.join(['%s\0%d\n' % (f, o) for f, o in offsets])
         self.file.write(d)
         self.file.flush()
 
+        d = ''.join(['%s\0%s\0' % (f, b) for f, b in backups])
+        self.backupsfile.write(d)
+        self.backupsfile.flush()
+
     @active
     def add(self, file, offset, data=None):
-        if file in self.map:
+        if file in self.map or file in self.backupmap:
             return
         if self._queue:
-            self._queue[-1].append((file, offset, data))
+            self._queue[-1][0].append((file, offset, data))
             return
 
         self.entries.append((file, offset, data))
         self.map[file] = len(self.entries) - 1
         # add enough data to the journal to do the truncate
         self.file.write("%s\0%d\n" % (file, offset))
         self.file.flush()
 
     @active
+    def addbackup(self, file, hardlink=True):
+        """Adds a backup of the file to the transaction
+
+        Calling addbackup() creates a hardlink backup of the specified file
+        that is used to recover the file in the event of the transaction
+        aborting.
+
+        * `file`: the file path, relative to .hg/store
+        * `hardlink`: use a hardlink to quickly create the backup
+        """
+
+        if file in self.map or file in self.backupmap:
+            return
+        backupfile = "journal.%s" % file
+        if self.opener.exists(file):
+            filepath = self.opener.join(file)
+            backuppath = self.opener.join(backupfile)
+            util.copyfiles(filepath, backuppath, hardlink=hardlink)
+        else:
+            self.add(file, 0)
+            return
+
+        if self._queue:
+            self._queue[-1][1].append((file, backupfile))
+            return
+
+        self.backupentries.append((file, backupfile, None))
+        self.backupmap[file] = len(self.backupentries) - 1
+        self.backupsfile.write("%s\0%s\0" % (file, backupfile))
+        self.backupsfile.flush()
+
+    @active
     def find(self, file):
         if file in self.map:
             return self.entries[self.map[file]]
+        if file in self.backupmap:
+            return self.backupentries[self.backupmap[file]]
         return None
 
     @active
     def replace(self, file, offset, data=None):
         '''
         replace can only replace already committed entries
         that are not pending in the queue
         '''
 
         if file not in self.map:
             raise KeyError(file)
         index = self.map[file]
         self.entries[index] = (file, offset, data)
         self.file.write("%s\0%d\n" % (file, offset))
         self.file.flush()
 
     @active
     def nest(self):
         self.count += 1
         self.usages += 1
         return self
 
     def release(self):
         if self.count > 0:
             self.usages -= 1
         # if the transaction scopes are left without being closed, fail
         if self.count > 0 and self.usages == 0:
             self._abort()
 
     def running(self):
         return self.count > 0
 
     @active
     def close(self):
         '''commit the transaction'''
         if self.count == 1 and self.onclose is not None:
             self.onclose()
 
         self.count -= 1
         if self.count != 0:
             return
         self.file.close()
         self.entries = []
         if self.after:
             self.after()
         if self.opener.isfile(self.journal):
             self.opener.unlink(self.journal)
+        if self.opener.isfile(self.backupjournal):
+            self.opener.unlink(self.backupjournal)
+            for f, b, _ in self.backupentries:
+                self.opener.unlink(b)
+        self.backupentries = []
         self.journal = None
 
     @active
     def abort(self):
         '''abort the transaction (generally called on error, or when the
         transaction is not explicitly committed before going out of
         scope)'''
         self._abort()
 
     def _abort(self):
         self.count = 0
         self.usages = 0
         self.file.close()
 
         if self.onabort is not None:
             self.onabort()
 
         try:
-            if not self.entries:
+            if not self.entries and not self.backupentries:
                 if self.journal:
                     self.opener.unlink(self.journal)
+                if self.backupjournal:
+                    self.opener.unlink(self.backupjournal)
                 return
 
             self.report(_("transaction abort!\n"))
 
             try:
                 _playback(self.journal, self.report, self.opener,
-                          self.entries, False)
+                          self.entries, self.backupentries, False)
                 self.report(_("rollback completed\n"))
             except Exception:
                 self.report(_("rollback failed - please run hg recover\n"))
         finally:
             self.journal = None
 
 
 def rollback(opener, file, report):
+    """Rolls back the transaction contained in the given file
+
+    Reads the entries in the specified file, and the corresponding
+    '*.backupfiles' file, to recover from an incomplete transaction.
+
+    * `file`: a file containing a list of entries, specifying where
+    to truncate each file.  The file should contain a list of
+    file\0offset pairs, delimited by newlines. The corresponding
+    '*.backupfiles' file should contain a list of file\0backupfile
+    pairs, delimited by \0.
+    """
     entries = []
+    backupentries = []
 
     fp = opener.open(file)
     lines = fp.readlines()
     fp.close()
     for l in lines:
         try:
             f, o = l.split('\0')
             entries.append((f, int(o), None))
         except ValueError:
             report(_("couldn't read journal entry %r!\n") % l)
 
-    _playback(file, report, opener, entries)
+    backupjournal = "%s.backupfiles" % file
+    if opener.exists(backupjournal):
+        fp = opener.open(backupjournal)
+        data = fp.read()
+        if len(data) > 0:
+            parts = data.split('\0')
+            for i in xrange(0, len(parts), 2):
+                f, b = parts[i:i + 1]
+                backupentries.append((f, b, None))
+
+    _playback(file, report, opener, entries, backupentries)