public GitLogProvider(
     @NotNull Project project,
     @NotNull GitRepositoryManager repositoryManager,
     @NotNull VcsLogObjectsFactory factory,
     @NotNull GitUserRegistry userRegistry) {
   myProject = project;
   myRepositoryManager = repositoryManager;
   myUserRegistry = userRegistry;
   myRefSorter = new GitRefManager(myRepositoryManager);
   myVcsObjectsFactory = factory;
   myVcs = ObjectUtils.assertNotNull(GitVcs.getInstance(project));
 }
  @NotNull
  @Override
  public DetailedLogData readFirstBlock(
      @NotNull VirtualFile root, @NotNull Requirements requirements) throws VcsException {
    if (!isRepositoryReady(root)) {
      return LogDataImpl.empty();
    }
    GitRepository repository =
        ObjectUtils.assertNotNull(myRepositoryManager.getRepositoryForRoot(root));

    // need to query more to sort them manually; this doesn't affect performance: it is equal for
    // -1000 and -2000
    int commitCount = requirements.getCommitCount() * 2;

    String[] params =
        new String[] {"HEAD", "--branches", "--remotes", "--max-count=" + commitCount};
    // NB: not specifying --tags, because it introduces great slowdown if there are many tags,
    // but makes sense only if there are heads without branch or HEAD labels (rare case). Such cases
    // are partially handled below.

    boolean refresh =
        requirements instanceof VcsLogProviderRequirementsEx
            && ((VcsLogProviderRequirementsEx) requirements).isRefresh();

    DetailedLogData data = GitHistoryUtils.loadMetadata(myProject, root, true, params);

    Set<VcsRef> safeRefs = data.getRefs();
    Set<VcsRef> allRefs = new OpenTHashSet<VcsRef>(safeRefs, DONT_CONSIDER_SHA);
    Set<VcsRef> branches = readBranches(repository);
    addNewElements(allRefs, branches);

    Collection<VcsCommitMetadata> allDetails;
    Set<String> currentTagNames = null;
    DetailedLogData commitsFromTags = null;
    if (!refresh) {
      allDetails = data.getCommits();
    } else {
      // on refresh: get new tags, which point to commits not from the first block; then get
      // history, walking down just from these tags
      // on init: just ignore such tagged-only branches. The price for speed-up.
      VcsLogProviderRequirementsEx rex = (VcsLogProviderRequirementsEx) requirements;

      currentTagNames = readCurrentTagNames(root);
      addOldStillExistingTags(allRefs, currentTagNames, rex.getPreviousRefs());

      allDetails = newHashSet(data.getCommits());

      Set<String> previousTags =
          newHashSet(ContainerUtil.mapNotNull(rex.getPreviousRefs(), GET_TAG_NAME));
      Set<String> safeTags = newHashSet(ContainerUtil.mapNotNull(safeRefs, GET_TAG_NAME));
      Set<String> newUnmatchedTags = remove(currentTagNames, previousTags, safeTags);

      if (!newUnmatchedTags.isEmpty()) {
        commitsFromTags = loadSomeCommitsOnTaggedBranches(root, commitCount, newUnmatchedTags);
        addNewElements(allDetails, commitsFromTags.getCommits());
        addNewElements(allRefs, commitsFromTags.getRefs());
      }
    }

    StopWatch sw = StopWatch.start("sorting commits in " + root.getName());
    List<VcsCommitMetadata> sortedCommits = VcsLogSorter.sortByDateTopoOrder(allDetails);
    sortedCommits =
        sortedCommits.subList(0, Math.min(sortedCommits.size(), requirements.getCommitCount()));
    sw.report();

    if (LOG.isDebugEnabled()) {
      validateDataAndReportError(
          root, allRefs, sortedCommits, data, branches, currentTagNames, commitsFromTags);
    }

    return new LogDataImpl(allRefs, sortedCommits);
  }