[DRAFT] Require locking agreement to ChangeView and allowing committed nodes to move to higher views

neo/Consensus/ChangeView.cs

@@ -7,14 +7,22 @@ public class ChangeView : ConsensusMessage
  public byte NewViewNumber;
  /// <summary>
  /// Timestamp of when the ChangeView message was created. This allows receiving nodes to ensure
- // they only respond once to a specific ChangeView request (it thus prevents replay of the ChangeView
- // message from repeatedly broadcasting RecoveryMessages).
+ /// they only respond once to a specific ChangeView request (it thus prevents replay of the ChangeView
+ /// message from repeatedly broadcasting RecoveryMessages).
  /// </summary>
  public uint Timestamp;
+ /// <summary>
+ /// Flag whether the node is locked/committed to change view from it's current view.
+ /// If not set, this indicates this is a request to change view, but not a commitment, and therefore it may
+ /// still accept further preparations and commit to generate a block in the current view.
+ /// If set, this node is locked to change view, and will not accept further preparations in the current view.
+ /// </summary>
+ public bool Locked;
 
  public override int Size => base.Size
  + sizeof(byte) //NewViewNumber
- + sizeof(uint); //Timestamp
+ + sizeof(uint) //Timestamp
+ + sizeof(bool); //Committed
 
  public ChangeView()
  : base(ConsensusMessageType.ChangeView)
@@ -26,13 +34,15 @@ public override void Deserialize(BinaryReader reader)
  base.Deserialize(reader);
  NewViewNumber = reader.ReadByte();
  Timestamp = reader.ReadUInt32();
+ Locked = reader.ReadBoolean();
  }
 
  public override void Serialize(BinaryWriter writer)
  {
  base.Serialize(writer);
  writer.Write(NewViewNumber);
  writer.Write(Timestamp);
+ writer.Write(Locked);
  }
  }
 }

neo/Consensus/ConsensusContext.cs

@@ -137,21 +137,23 @@ public bool Load()
 
  public ConsensusPayload MakeChangeView(byte newViewNumber)
  {
+ var changeViewLockedCount = ChangeViewPayloads.Count(p => p != null && p.GetDeserializedMessage<ChangeView>().NewViewNumber > ViewNumber);
+ if (ChangeViewPayloads[MyIndex]?.GetDeserializedMessage<ChangeView>().NewViewNumber <= ViewNumber && newViewNumber > ViewNumber)
+ changeViewLockedCount++;
  return ChangeViewPayloads[MyIndex] = MakeSignedPayload(new ChangeView
  {
  NewViewNumber = newViewNumber,
- Timestamp = TimeProvider.Current.UtcNow.ToTimestamp()
+ Timestamp = TimeProvider.Current.UtcNow.ToTimestamp(),
+ Locked = changeViewLockedCount >= this.M() && !(this.ResponseSent() || this.IsPrimary())
  });
  }
 
  public ConsensusPayload MakeCommit()
  {
- if (CommitPayloads[MyIndex] == null)
- CommitPayloads[MyIndex] = MakeSignedPayload(new Commit
- {
- Signature = MakeHeader()?.Sign(keyPair)
- });
- return CommitPayloads[MyIndex];
+ return CommitPayloads[MyIndex] ?? (CommitPayloads[MyIndex] = MakeSignedPayload(new Commit
+ {
+ Signature = MakeHeader()?.Sign(keyPair)
+ }));
  }
 
  private Block _header = null;
@@ -235,6 +237,7 @@ public ConsensusPayload MakeRecoveryMessage()
  }
  return MakeSignedPayload(new RecoveryMessage()
  {
+ Timestamp = TimeProvider.Current.UtcNow.ToTimestamp(),
  ChangeViewMessages = LastChangeViewPayloads.Where(p => p != null).Select(p => RecoveryMessage.ChangeViewPayloadCompact.FromPayload(p)).Take(this.M()).ToDictionary(p => (int)p.ValidatorIndex),
  PrepareRequestMessage = prepareRequestMessage,
  // We only need a PreparationHash set if we don't have the PrepareRequest information.
@@ -280,10 +283,14 @@ public void Reset(byte viewNumber)
  else
  {
  for (int i = 0; i < LastChangeViewPayloads.Length; i++)
- if (ChangeViewPayloads[i]?.GetDeserializedMessage<ChangeView>().NewViewNumber == viewNumber)
+ {
+ var changeViewMessage = ChangeViewPayloads[i]?.GetDeserializedMessage<ChangeView>();
+ if (changeViewMessage?.NewViewNumber == viewNumber && changeViewMessage.Locked)
  LastChangeViewPayloads[i] = ChangeViewPayloads[i];
  else
  LastChangeViewPayloads[i] = null;
+ }
+
  }
  ViewNumber = viewNumber;
  PrimaryIndex = this.GetPrimaryIndex(viewNumber);