Helium: Adding vector clock

blimp/net/helium/vector_clock.cc

+// 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) {}

[Kevin M, 2016/09/28 01:23:15]

Put the zeroes in the .h as inline initializers

[scf, 2016/09/28 16:40:37]

Done.

+
+VectorClock::VectorClock(Revision local_revision, Revision remote_revision)
+    : local_revision_(local_revision), remote_revision_(remote_revision) {}
+
+VectorClock::Comparison VectorClock::CompareTo(const VectorClock& other) const {
+  DCHECK(local_revision_ >= other.local_revision());
+
+  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 {
+        DLOG(FATAL) << "Local revision should always be greater or equal.";

[Kevin M, 2016/09/28 01:23:15]

This state is pretty messed up, right? Maybe we should just LOG(FATAL) and crash
outright on release builds. Debug builds will never hit this line; the DCHECK on
line 19 will abort execution.

[scf, 2016/09/28 16:40:37]

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() {
+  local_revision_++;
+}
+
+}  // namespace blimp