blockchain: Cleanup and optimize stake node logic.

This reworks the stake node handling logic a bit to clean it up,
slightly optimize it, and to make it easier to decouple the chain
processing and connection code from the download logic in the future.

To accomplish this, the fetchStakeNode dependence on the
getReorganizeNodes function is removed in favor of directly iterating
the block nodes in the function as needed.  Not only is this more
efficient, it also allows the function to return stake nodes for
branches regardless of their validation status.  Currently, this is
irrelevant due to the connection and download logic being tightly
coupled.  However, it will be necessary in the future when those are
separated.

Also, the flushing and pruning logic is modified to no longer rely on
the download logic being tightly coupled to the the connection logic.
In particular, a new function named flushBlockIndex is added as a
wrapper to the index flush function which populates stake information in
a node before flushing it to the database as needed, and all flushing
invocations use the wrapper instead.

Finally, the stakeUndoData field is removed since it is only used to
avoid some database loads on reorgs that are large enough to exceed the
pruning depth, which never happens in practice anyway, so there is no
point in using up extra memory for it.

blockchain/accept.go

@@ -80,7 +80,7 @@ func (b *BlockChain) maybeAcceptBlock(block *dcrutil.Block, flags BehaviorFlags)
 	b.index.AddNode(newNode)
 
 	// Ensure the new block index entry is written to the database.
-	err = b.index.flush()
+	err = b.flushBlockIndex()
 	if err != nil {
 		return 0, err
 	}
@@ -111,7 +111,6 @@ func (b *BlockChain) maybeAcceptBlock(block *dcrutil.Block, flags BehaviorFlags)
 		if err != nil {
 			return 0, err
 		}
-		newNode.stakeUndoData = newNode.stakeNode.UndoData()
 	}
 
 	// Grab the parent block since it is required throughout the block

blockchain/blockindex.go

@@ -121,7 +121,6 @@ type blockNode struct {
 	// evaluation of sidechains.
 	stakeNode      *stake.Node
 	newTickets     []chainhash.Hash
-	stakeUndoData  stake.UndoTicketDataSlice
 	ticketsVoted   []chainhash.Hash
 	ticketsRevoked []chainhash.Hash
 
@@ -227,7 +226,7 @@ func (node *blockNode) lotteryIV() chainhash.Hash {
 // node.
 //
 // This function is NOT safe for concurrent access.  It must only be called when
-// initially creating a node.
+// initially creating a node or when protected by the chain lock.
 func (node *blockNode) populateTicketInfo(spentTickets *stake.SpentTicketsInBlock) {
 	node.ticketsVoted = spentTickets.VotedTickets
 	node.ticketsRevoked = spentTickets.RevokedTickets

blockchain/chain.go

@@ -631,7 +631,6 @@ func (b *BlockChain) pruneStakeNodes() {
 		// for example if you're adding an old side chain block.
 		if node.height > b.bestChain.Tip().height-minMemoryNodes {
 			node.stakeNode = nil
-			node.stakeUndoData = nil
 			node.newTickets = nil
 			node.ticketsVoted = nil
 			node.ticketsRevoked = nil
@@ -696,7 +695,7 @@ func (b *BlockChain) getReorganizeNodes(node *blockNode) (*list.List, *list.List
 		return detachNodes, attachNodes
 	}
 
-	// Do not allow a reorganize to a known invalid chain.	Note that all
+	// Do not allow a reorganize to a known invalid chain.  Note that all
 	// intermediate ancestors other than the direct parent are also checked
 	// below, however, this check allows extra to work to be avoided in the
 	// majority of cases since reorgs across multiple unvalidated blocks are
@@ -784,7 +783,7 @@ func (b *BlockChain) connectBlock(node *blockNode, block, parent *dcrutil.Block,
 
 	// Write any modified block index entries to the database before
 	// updating the best state.
-	if err := b.index.flush(); err != nil {
+	if err := b.flushBlockIndex(); err != nil {
 		return err
 	}
 
@@ -929,7 +928,6 @@ func (b *BlockChain) connectBlock(node *blockNode, block, parent *dcrutil.Block,
 	if node.height < b.chainParams.LatestCheckpointHeight() {
 		parent := b.bestChain.Tip().parent
 		parent.stakeNode = nil
-		parent.stakeUndoData = nil
 		parent.newTickets = nil
 		parent.ticketsVoted = nil
 		parent.ticketsRevoked = nil
@@ -963,7 +961,7 @@ func (b *BlockChain) disconnectBlock(node *blockNode, block, parent *dcrutil.Blo
 
 	// Write any modified block index entries to the database before
 	// updating the best state.
-	if err := b.index.flush(); err != nil {
+	if err := b.flushBlockIndex(); err != nil {
 		return err
 	}
 
@@ -1559,6 +1557,22 @@ func (b *BlockChain) ForceHeadReorganization(formerBest chainhash.Hash, newBest
 	return err
 }
 
+// flushBlockIndex populates any ticket data that has been pruned from modified
+// block nodes, writes those nodes to the database and clears the set of
+// modified nodes if it succeeds.
+func (b *BlockChain) flushBlockIndex() error {
+	b.index.RLock()
+	for node := range b.index.modified {
+		if err := b.maybeFetchTicketInfo(node); err != nil {
+			b.index.RUnlock()
+			return err
+		}
+	}
+	b.index.RUnlock()
+
+	return b.index.flush()
+}
+
 // flushBlockIndexWarnOnly attempts to flush and modified block index nodes to
 // the database and will log a warning if it fails.
 //
@@ -1567,7 +1581,7 @@ func (b *BlockChain) ForceHeadReorganization(formerBest chainhash.Hash, newBest
 // to be validated again.  All other cases must directly call the function on
 // the block index and check the error return accordingly.
 func (b *BlockChain) flushBlockIndexWarnOnly() {
-	if err := b.index.flush(); err != nil {
+	if err := b.flushBlockIndex(); err != nil {
 		log.Warnf("Unable to flush block index changes to db: %v", err)
 	}
 }

blockchain/chainio.go

@@ -1749,7 +1749,6 @@ func (b *BlockChain) initChainState() error {
 			if err != nil {
 				return err
 			}
-			tip.stakeUndoData = tip.stakeNode.UndoData()
 			tip.newTickets = tip.stakeNode.NewTickets()
 		}
 

blockchain/stakeext.go

@@ -35,11 +35,11 @@ func (b *BlockChain) NextLotteryData() ([]chainhash.Hash, int, [6]byte, error) {
 // with the chainLock held for writes.
 func (b *BlockChain) lotteryDataForNode(node *blockNode) ([]chainhash.Hash, int, [6]byte, error) {
 	if node.height < b.chainParams.StakeEnabledHeight {
-		return []chainhash.Hash{}, 0, [6]byte{}, nil
+		return nil, 0, [6]byte{}, nil
 	}
 	stakeNode, err := b.fetchStakeNode(node)
 	if err != nil {
-		return []chainhash.Hash{}, 0, [6]byte{}, err
+		return nil, 0, [6]byte{}, err
 	}
 
 	return stakeNode.Winners(), stakeNode.PoolSize(), stakeNode.FinalState(), nil