Helium: Adding vector clock

blimp/net/helium/vector_clock.h

Index: blimp/net/helium/vector_clock.h
diff --git a/blimp/net/helium/vector_clock.h b/blimp/net/helium/vector_clock.h
new file mode 100644
index 0000000000000000000000000000000000000000..56c90cbe088313ba6c6e879d5e433d21c05f7700
--- /dev/null
+++ b/blimp/net/helium/vector_clock.h
@@ -0,0 +1,34 @@
+// 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.
+
+#ifndef BLIMP_NET_HELIUM_VECTOR_CLOCK_H_
+#define BLIMP_NET_HELIUM_VECTOR_CLOCK_H_
+
+#include <cinttypes>

[Kevin M, 2016/09/27 17:31:10]

<stdint.h> is used more frequently

[scf, 2016/09/27 18:29:59]

Done.

+
+#include "blimp/net/blimp_net_export.h"
+
+namespace blimp {
+
+class BLIMP_NET_EXPORT VectorClock {

[Kevin M, 2016/09/27 17:31:10]

Add comment to class describing what vector clocks do, how this class implements
them, where it might be used, and links to reference materials. A lot of people
are unfamiliar with vector clocks so this file will be the first place they'll
look for more information.

[scf, 2016/09/27 18:29:59]

Done.

+ public:
+  VectorClock(int32_t local_revision, int32_t remote_revision);

[Kevin M, 2016/09/27 17:31:10]

Does it make sense to have a default -public constructor for this class, or
should we declare it under private?

[scf, 2016/09/27 18:29:59]

Agree, default public makes sense.

+
+  enum class Comparison { LessThan, EqualTo, GreaterThan, Conflicts };

[Kevin M, 2016/09/27 17:31:10]

Enums go at the top of public:

[Kevin M, 2016/09/27 17:31:10]

Potentially misguided language nit:

What about "Conflict", singular? Otherwise we would need "ConflictsWith" if we
maintained the convention of the previous three items.

[scf, 2016/09/27 18:29:59]

Done.

[scf, 2016/09/27 18:29:59]

Done.

+
+  Comparison CompareTo(const VectorClock& other) const;

[Kevin M, 2016/09/27 17:31:10]

Add comments for all public members except maybe the revision getters (those are
pretty obvious)

[scf, 2016/09/27 18:29:59]

Done.

+  VectorClock MergeWith(const VectorClock& other);
+  void IncrementLocal();
+
+  int32_t local_revision() { return local_revision_; }
+  int32_t remote_revision() { return remote_revision_; }
+
+ private:
+  int32_t local_revision_ = 0;
+  int32_t remote_revision_ = 0;
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_HELIUM_VECTOR_CLOCK_H_