Fix ConsensusContext.CreateContext()

[greymistcube]

There are numerous issues related to this problem.

• CreateContext() can create a Context with a wrong ValidatorSet

  libplanet/Libplanet.Net/Consensus/ConsensusContext.cs

  Lines 455 to 461 in 7bbce0e

  	if (_blockChain.Tip.ProtocolVersion
  	< BlockMetadata.SlothProtocolVersion)
  	{
  	validatorSet = _blockChain
  	.GetWorldState(_blockChain[Height - 1].StateRootHash)
  	.GetValidatorSet();
  	}

  • CreateContext() can be called with any height that is greater than or equal to Height, meaning it is impossible to know the ValidatorSet for given height if height is greater than Height.
• HandleMessage() can lock the entire ConsensusContext

  libplanet/Libplanet.Net/Consensus/ConsensusContext.cs

  Lines 252 to 275 in 7bbce0e

  	public bool HandleMessage(ConsensusMsg consensusMessage)
  	{
  	long height = consensusMessage.Height;
  	if (height < Height)
  	{
  	_logger.Debug(
  	"Discarding a received message as its height #{MessageHeight} " +
  	"is lower than the current context's height #{ContextHeight}",
  	height,
  	Height);
  	return false;
  	}
  	lock (_contextLock)
  	{
  	if (!_contexts.ContainsKey(height))
  	{
  	_contexts[height] = CreateContext(height);
  	}
  	_contexts[height].ProduceMessage(consensusMessage);
  	return true;
  	}
  	}

  • When ConsensusMsgs with "future" heights are received, it gets funneled to HandleMessage(), and this would result in a lock until the first call to GetNextStateRootHash() is resolved.

It is hard to know the full extent of the problem as this may cause issues on very non-trivial edge cases. The issue is farther exacerbated by having the value of Height becoming further asynchronous with the state of BlockChain the ConsensusContext is referencing.