Helium: Adding vector clock

blimp/net/helium/vector_clock.cc

Index: blimp/net/helium/vector_clock.cc
diff --git a/blimp/net/helium/vector_clock.cc b/blimp/net/helium/vector_clock.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f31181086e80f1be9030a3e61011c3d681c7ee3e
--- /dev/null
+++ b/blimp/net/helium/vector_clock.cc
@@ -0,0 +1,56 @@
+// Copyright 2016 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 "blimp/net/helium/vector_clock.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+
+namespace blimp {
+
+VectorClock::VectorClock() : local_revision_(0), remote_revision_(0) {}
+
+VectorClock::VectorClock(int32_t local_revision, int32_t remote_revision)
+    : local_revision_(local_revision), remote_revision_(remote_revision) {}
+
+VectorClock::Comparison VectorClock::CompareTo(const VectorClock& other) const {
+  DCHECK(local_revision() >= other.local_revision());

[Kevin M, 2016/09/27 21:36:09]

add blank line below dchecks

[scf, 2016/09/27 23:23:10]

Done.

+  if (local_revision() == other.local_revision()) {
+    if (remote_revision() == other.remote_revision()) {
+      return VectorClock::Comparison::EqualTo;
+    } else if (remote_revision() < other.remote_revision()) {
+      return VectorClock::Comparison::LessThan;
+    } else {
+      return VectorClock::Comparison::GreaterThan;
+    }
+  } else {
+    if (local_revision() > other.local_revision()) {
+      if (remote_revision() == other.remote_revision()) {
+        return VectorClock::Comparison::GreaterThan;
+      } else {
+        return VectorClock::Comparison::Conflict;
+      }
+    } else {  // We know its not equal or greater, so its smaller
+      if (remote_revision() == other.remote_revision()) {
+        return VectorClock::Comparison::LessThan;
+      } else {
+        DCHECK(false) << "Local revision should always be greater or equal.";

[Kevin M, 2016/09/27 21:36:09]

* Already checked in the top of CompareTo.
* No need to add explanation; that DCHECK body is self explanatory.
* DCHECK(false) should be DLOG(FATAL)

[scf, 2016/09/27 23:23:10]

Done.

+        return VectorClock::Comparison::Conflict;
+      }
+    }
+  }
+}
+
+VectorClock VectorClock::MergeWith(const VectorClock& other) const {
+  VectorClock result(std::max(local_revision(), other.local_revision()),
+                     std::max(remote_revision(), other.remote_revision()));
+  return result;
+}
+
+void VectorClock::IncrementLocal() {
+  set_local_revision(local_revision() + 1);

[Kevin M, 2016/09/27 21:36:09]

Accesses to members of |this| needn't be mediated by setters/getters. My
previous comment was more relevant to accessing state in other objects.

[scf, 2016/09/27 23:23:10]

Done.

+}
+
+}  // namespace blimp