multi: add BgBlkTmplGenerator.

BgBlkTmplGenerator represents the background process that
generates block templates and notifies all subscribed clients
on template regeneration. It generates new templates based
on mempool activity for vote and non-vote transactions and
the time elapsed since last template regeneration.

This also adds a template pool to the background block
generator for recreating submitted blocks.

blockchain/process.go

@@ -91,6 +91,12 @@ func (b *BlockChain) processOrphans(hash *chainhash.Hash, flags BehaviorFlags) e
 	return nil
 }
 
+// WaitForChain blocks if the chain is processing a block or handling a reorg.
+func (b *BlockChain) WaitForChain() {
+	b.chainLock.RLock()
+	b.chainLock.RUnlock()
+}
+
 // ProcessBlock is the main workhorse for handling insertion of new blocks into
 // the block chain.  It includes functionality such as rejecting duplicate
 // blocks, ensuring blocks follow all rules, orphan handling, and insertion into

blockmanager.go

@@ -300,6 +300,7 @@ type headerNode struct {
 // incoming blocks.
 type blockManager struct {
 	server              *server
+	g                   *BgBlkTmplGenerator
 	started             int32
 	shutdown            int32
 	chain               *blockchain.BlockChain
@@ -1896,6 +1897,10 @@ func (b *blockManager) handleNotifyMsg(notification *blockchain.Notification) {
 			r.ntfnMgr.NotifyBlockConnected(block)
 		}
 
+		if b.server.bg != nil {
+			b.server.bg.handleConnectedBlock(block.Height())
+		}
+
 	// Stake tickets are spent or missed from the most recently connected block.
 	case blockchain.NTSpentAndMissedTickets:
 		tnd, ok := notification.Data.(*blockchain.TicketNotificationsData)
@@ -1987,6 +1992,14 @@ func (b *blockManager) handleNotifyMsg(notification *blockchain.Notification) {
 		handleDisconnectedBlockTxns(block.Transactions()[1:])
 		handleDisconnectedBlockTxns(block.STransactions())
 
+		if b.server.bg != nil {
+			b.server.bg.handleDisconnectedBlock(block.Height())
+		}
+
+		// Filter and update the rebroadcast inventory.
+		b.server.PruneRebroadcastInventory()
+
+		// Notify registered websocket clients.
 		if r := b.server.rpcServer; r != nil {
 			// Filter and update the rebroadcast inventory.
 			b.server.PruneRebroadcastInventory()
@@ -1995,6 +2008,18 @@ func (b *blockManager) handleNotifyMsg(notification *blockchain.Notification) {
 			r.ntfnMgr.NotifyBlockDisconnected(block)
 		}
 
+	// Chain reorganization has commenced.
+	case blockchain.NTChainReorgStarted:
+		if b.server.bg != nil {
+			b.server.bg.handleChainReorgStarted()
+		}
+
+	// Chain reorganization has concluded.
+	case blockchain.NTChainReorgDone:
+		if b.server.bg != nil {
+			b.server.bg.handleChainReorgDone()
+		}
+
 	// The blockchain is reorganizing.
 	case blockchain.NTReorganization:
 		rd, ok := notification.Data.(*blockchain.ReorganizationNtfnsData)

mempool/mempool.go

@@ -123,6 +123,10 @@ type Config struct {
 	// to use for indexing the unconfirmed transactions in the memory pool.
 	// This can be nil if the address index is not enabled.
 	ExistsAddrIndex *indexers.ExistsAddrIndex
+
+	// OnVoteReceived defines the function used to signal receiving a new
+	// vote in the mempool.
+	OnVoteReceived func(voteTx *wire.MsgTx)
 }
 
 // Policy houses the policy (configuration parameters) which is used to
@@ -645,6 +649,9 @@ func (mp *TxPool) RemoveDoubleSpends(tx *dcrutil.Tx) {
 // This function MUST be called with the mempool lock held (for writes).
 func (mp *TxPool) addTransaction(utxoView *blockchain.UtxoViewpoint,
 	tx *dcrutil.Tx, txType stake.TxType, height int64, fee int64) {
+	if txType == stake.TxTypeSSGen {
+		mp.cfg.OnVoteReceived(tx.MsgTx())
+	}
 
 	// Add the transaction to the pool and mark the referenced outpoints
 	// as spent by the pool.
@@ -1597,8 +1604,12 @@ func (mp *TxPool) LastUpdated() time.Time {
 // New returns a new memory pool for validating and storing standalone
 // transactions until they are mined into a block.
 func New(cfg *Config) *TxPool {
+	cfgCopy := *cfg
+	if cfgCopy.OnVoteReceived == nil {
+		cfgCopy.OnVoteReceived = func(tx *wire.MsgTx) {}
+	}
 	return &TxPool{
-		cfg:           *cfg,
+		cfg:           cfgCopy,
 		pool:          make(map[chainhash.Hash]*TxDesc),
 		orphans:       make(map[chainhash.Hash]*dcrutil.Tx),
 		orphansByPrev: make(map[wire.OutPoint]map[chainhash.Hash]*dcrutil.Tx),

mempool/mempool_test.go

@@ -611,6 +611,7 @@ func newPoolHarness(chainParams *chaincfg.Params) (*poolHarness, []spendableOutp
 			SigCache:            nil,
 			AddrIndex:           nil,
 			ExistsAddrIndex:     nil,
+			OnVoteReceived:      nil,
 		}),
 	}