mercurial/merge.py

48427:08b060abd658

            assert len(getfiledata) == (
                mresult.len((mergestatemod.ACTION_GET,)) if wantfiledata else 0
            )
            with repo.dirstate.parentchange():
                repo.setparents(fp1, fp2)
                mergestatemod.recordupdates(
                    repo, mresult.actionsdict, branchmerge, getfiledata
                )
                # update completed, clear state

48428:6dc3dc5e9636

            assert len(getfiledata) == (
                mresult.len((mergestatemod.ACTION_GET,)) if wantfiledata else 0
            )
            with repo.dirstate.parentchange():
                ### Filter Filedata
                #
                # We gathered "cache" information for the clean file while
                # updating them: mtime, size and mode.
                #
                # At the time this comment is written, they are various issues
                # with how we gather the `mode` and `mtime` information (see
                # the comment in `batchget`).
                #
                # We are going to smooth one of this issue here : mtime ambiguity.
                #
                # i.e. even if the mtime gathered during `batchget` was
                # correct[1] a change happening right after it could change the
                # content while keeping the same mtime[2].
                #
                # When we reach the current code, the "on disk" part of the
                # update operation is finished. We still assume that no other
                # process raced that "on disk" part, but we want to at least
                # prevent later file change to alter the content of the file
                # right after the update operation. So quickly that the same
                # mtime is record for the operation.
                # To prevent such ambiguity to happens, we will only keep the
                # "file data" for files with mtime that are stricly in the past,
                # i.e. whose mtime is strictly lower than the current time.
                #
                # This protect us from race conditions from operation that could
                # run right after this one, especially other Mercurial
                # operation that could be waiting for the wlock to touch files
                # content and the dirstate.
                #
                # In an ideal world, we could only get reliable information in
                # `getfiledata` (from `getbatch`), however the current approach
                # have been a successful compromise since many years.
                #
                # At the time this comment is written, not using any "cache"
                # file data at all here would not be viable. As it would result is
                # a very large amount of work (equivalent to the previous `hg
                # update` during the next status after an update).
                #
                # [1] the current code cannot grantee that the `mtime` and
                # `mode` are correct, but the result is "okay in practice".
                # (see the comment in `batchget`).                #
                #
                # [2] using nano-second precision can greatly help here because
                # it makes the "different write with same mtime" issue
                # virtually vanish. However, dirstate v1 cannot store such
                # precision and a bunch of python-runtime, operating-system and
                # filesystem does not provide use with such precision, so we
                # have to operate as if it wasn't available.
                if getfiledata:
                    ambiguous_mtime = {}
                    now = timestamp.get_fs_now(repo.vfs)
                    if now is None:
                        # we can't write to the FS, so we won't actually update
                        # the dirstate content anyway, no need to put cache
                        # information.
                        getfiledata = None
                    else:
                        now_sec = now[0]
                        for f, m in pycompat.iteritems(getfiledata):
                            if m is not None and m[2][0] >= now_sec:
                                ambiguous_mtime[f] = (m[0], m[1], None)
                        for f, m in pycompat.iteritems(ambiguous_mtime):
                            getfiledata[f] = m

                repo.setparents(fp1, fp2)
                mergestatemod.recordupdates(
                    repo, mresult.actionsdict, branchmerge, getfiledata
                )
                # update completed, clear state