sync: Introduce ModelTypeRegistry and helpers

sync/engine/committer_list.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sync/engine/committer_list.h"
+
+#include <map>
+
+#include "sync/engine/sync_directory_commit_contribution.h"
+#include "sync/engine/sync_directory_commit_contributor.h"
+#include "sync/protocol/sync.pb.h"
+
+namespace syncer {
+
+typedef std::map<ModelType, size_t> TypeToIndexMap;
+
+CommitterList::CommitterList()
+    : commit_contributor_deleter_(&commit_contributor_map_) {}
+
+CommitterList::~CommitterList() {}
+
+void CommitterList::RegisterType(
+    ModelType type,
+    SyncDirectoryCommitContributor* contributor) {
+  bool inserted =
+      commit_contributor_map_.insert(std::make_pair(type, contributor)).second;
+  DCHECK(inserted) << "Attempt to override existing type handler in map";
+}
+
+void CommitterList::GatherCommitContributions(
+    ModelTypeSet commit_types,
+    size_t max_entries,
+    ContributionMap* contributions) {
+  size_t num_entries = 0;
+  for (ModelTypeSet::Iterator it = commit_types.First();
+       it.Good(); it.Inc()) {
+    CommitContributorMap::iterator cm_it =
+        commit_contributor_map_.find(it.Get());
+    if (cm_it == commit_contributor_map_.end()) {
+      NOTREACHED()
+          << "Could not find requested type " << ModelTypeToString(it.Get())
+          << " in contributor map.";
+      continue;
+    }
+    size_t spaces_remaining = max_entries - num_entries;
+    SyncDirectoryCommitContribution* contribution =
+        cm_it->second->GetContribution(spaces_remaining);
+    if (contribution) {
+      num_entries += contribution->GetNumEntries();
+      contributions->insert(std::make_pair(it.Get(), contribution));
+    }
+    if (num_entries == max_entries) {

[Nicolas Zea, 2014/01/07 23:11:40]

I think it's a bit cleaner to write this as:
if (num >= max) {
  DCHECK_EQ(num, max) << "...";
  break;
}

[rlarocque, 2014/01/08 01:37:24]

Done.

+      break;  // No point in continuting to iterate in this case.
+    } else if (num_entries > max_entries) {
+      NOTREACHED() << "Number of commit entries exceeds maximum.";
+      break;  // This should never happen, but let's exit early if it does.
+    }
+  }
+}
+
+}  // namespace syncer