core: refactor witness data processing flow (#124)

Since witness data need to include data from application after it
processed a block (e.g. stateRoot).  We should make the process of
witness data asynchronous.

An interface `BlockProcessedChan()` is added to the application
interface to return a channel for notifying the consensus core when a
block is processed. The notification object includes a byte slice
(witenss data) which will be include in the final witness data object.

1 files changed, 4 insertions, 0 deletions

diff --git a/core/interfaces.go b/core/interfaces.go
index 4f67e1e..8ecfb3c 100644
--- a/core/interfaces.go
+++ b/core/interfaces.go
@@ -46,6 +46,10 @@ type Application interface {
 	// DeliverBlock is called when a block is add to the compaction chain.
 	DeliverBlock(blockHash common.Hash, timestamp time.Time)
 
+	// BlockProcessedChan returns a channel to receive the block hashes that have
+	// finished processing by the application.
+	BlockProcessedChan() <-chan types.WitnessResult
+
 	// WitnessAckDeliver is called when a witness ack is created.
 	WitnessAckDeliver(witnessAck *types.WitnessAck)
 }