comparison mercurial/localrepo.py @ 42546:904e0da2e195

merge with stable

42544:2702dfc7e029

        return cls(self, name, visibilityexceptions)

    @mixedrepostorecache(('bookmarks', 'plain'), ('bookmarks.current', 'plain'),
                         ('bookmarks', ''), ('00changelog.i', ''))
    def _bookmarks(self):
        # Since the multiple files involved in the transaction cannot be
        # written atomically (with current repository format), there is a race
        # condition here.
        #
        # 1) changelog content A is read
        # 2) outside transaction update changelog to content B
        # 3) outside transaction update bookmark file referring to content B
        # 4) bookmarks file content is read and filtered against changelog-A
        #
        # When this happens, bookmarks against nodes missing from A are dropped.
        #
        # Having this happening during read is not great, but it become worse
        # when this happen during write because the bookmarks to the "unknown"
        # nodes will be dropped for good. However, writes happen within locks.
        # This locking makes it possible to have a race free consistent read.
        # For this purpose data read from disc before locking  are
        # "invalidated" right after the locks are taken. This invalidations are
        # "light", the `filecache` mechanism keep the data in memory and will
        # reuse them if the underlying files did not changed. Not parsing the
        # same data multiple times helps performances.
        #
        # Unfortunately in the case describe above, the files tracked by the
        # bookmarks file cache might not have changed, but the in-memory
        # content is still "wrong" because we used an older changelog content
        # to process the on-disk data. So after locking, the changelog would be
        # refreshed but `_bookmarks` would be preserved.
        # Adding `00changelog.i` to the list of tracked file is not
        # enough, because at the time we build the content for `_bookmarks` in
        # (4), the changelog file has already diverged from the content used
        # for loading `changelog` in (1)
        #
        # To prevent the issue, we force the changelog to be explicitly
        # reloaded while computing `_bookmarks`. The data race can still happen
        # without the lock (with a narrower window), but it would no longer go
        # undetected during the lock time refresh.
        #
        # The new schedule is as follow
        #
        # 1) filecache logic detect that `_bookmarks` needs to be computed
        # 2) cachestat for `bookmarks` and `changelog` are captured (for book)
        # 3) We force `changelog` filecache to be tested
        # 4) cachestat for `changelog` are captured (for changelog)
        # 5) `_bookmarks` is computed and cached
        #
        # The step in (3) ensure we have a changelog at least as recent as the
        # cache stat computed in (1). As a result at locking time:
        #  * if the changelog did not changed since (1) -> we can reuse the data
        #  * otherwise -> the bookmarks get refreshed.
        self._refreshchangelog()
        return bookmarks.bmstore(self)

    def _refreshchangelog(self):
        """make sure the in memory changelog match the on-disk one"""
        if ('changelog' in vars(self) and self.currenttransaction() is None):

42546:904e0da2e195

        return cls(self, name, visibilityexceptions)

    @mixedrepostorecache(('bookmarks', 'plain'), ('bookmarks.current', 'plain'),
                         ('bookmarks', ''), ('00changelog.i', ''))
    def _bookmarks(self):
        return bookmarks.bmstore(self)

    def _refreshchangelog(self):
        """make sure the in memory changelog match the on-disk one"""
        if ('changelog' in vars(self) and self.currenttransaction() is None):