network: refactor notary service's PostBlock

There was a deadlock while trying to finalize transaction during
PostBlock:
	1) (*Notary).PostBlock is called under the blockchain lock
	2) (*Notary).onTransaction is called inside the PostBlock
	3) (*Notary).onTransaction needs to RLock the blockchain to add
completed transaction to the memory pool (and the blockchain is Lock'ed
by this moment)

The problem is fixed by using notifications subsistem, because it's not
required to call (*Notary).PostBlock under the blockchain lock.

pkg/core/notary_test.go

@@ -95,7 +95,7 @@ func TestNotary(t *testing.T) {
 
 	bc.SetNotary(ntr1)
 	bc.RegisterPostBlock(func(bc blockchainer.Blockchainer, pool *mempool.Pool, b *block.Block) {
-		ntr1.PostPersist(bc, pool, b)
+		ntr1.PostPersist()
 	})
 
 	notaryNodes := keys.PublicKeys{acc1.PrivateKey().PublicKey(), acc2.PrivateKey().PublicKey()}

pkg/network/server.go

@@ -158,9 +158,6 @@ func newServerFromConstructors(config ServerConfig, chain blockchainer.Blockchai
 			}
 			s.notaryModule = n
 			chain.SetNotary(n)
-			chain.RegisterPostBlock(func(bc blockchainer.Blockchainer, pool *mempool.Pool, b *block.Block) {
-				s.notaryModule.PostPersist(bc, pool, b)
-			})
 		}
 	} else if chain.GetConfig().P2PNotary.Enabled {
 		return nil, errors.New("P2PSigExtensions are disabled, but Notary service is enable")

pkg/services/notary/notary.go

@@ -45,6 +45,7 @@ type (
 		mp *mempool.Pool
 		// requests channel
 		reqCh    chan mempool.Event
+		blocksCh chan *block.Block
 		stopCh   chan struct{}
 	}
 
@@ -109,17 +110,20 @@ func NewNotary(bc blockchainer.Blockchainer, mp *mempool.Pool, log *zap.Logger,
 		onTransaction: onTransaction,
 		mp:            mp,
 		reqCh:         make(chan mempool.Event),
+		blocksCh:      make(chan *block.Block),
 		stopCh:        make(chan struct{}),
 	}, nil
 }
 
 // Run runs Notary module and should be called in a separate goroutine.
 func (n *Notary) Run() {
+	n.Config.Chain.SubscribeForBlocks(n.blocksCh)
 	n.mp.SubscribeForTransactions(n.reqCh)
 	for {
 		select {
 		case <-n.stopCh:
 			n.mp.UnsubscribeFromTransactions(n.reqCh)
+			n.Config.Chain.UnsubscribeFromBlocks(n.blocksCh)
 			return
 		case event := <-n.reqCh:
 			if req, ok := event.Data.(*payload.P2PNotaryRequest); ok {
@@ -130,6 +134,9 @@ func (n *Notary) Run() {
 					n.OnRequestRemoval(req)
 				}
 			}
+		case <-n.blocksCh:
+			// new block was added, need to check for valid fallbacks
+			n.PostPersist()
 		}
 	}
 }
@@ -259,16 +266,18 @@ func (n *Notary) OnRequestRemoval(pld *payload.P2PNotaryRequest) {
 	}
 }
 
-// PostPersist is a callback which is called after new block is persisted.
+// PostPersist is a callback which is called after new block event is received.
-func (n *Notary) PostPersist(bc blockchainer.Blockchainer, pool *mempool.Pool, b *block.Block) {
+// PostPersist must not be called under the blockchain lock, because it uses finalization function.
+func (n *Notary) PostPersist() {
 	if n.getAccount() == nil {
 		return
 	}
 
 	n.reqMtx.Lock()
 	defer n.reqMtx.Unlock()
+	currHeight := n.Config.Chain.BlockHeight()
 	for h, r := range n.requests {
-		if !r.isSent && r.typ != Unknown && r.nSigs == r.nSigsCollected && r.minNotValidBefore > bc.BlockHeight() {
+		if !r.isSent && r.typ != Unknown && r.nSigs == r.nSigsCollected && r.minNotValidBefore > currHeight {
 			if err := n.finalize(r.main); err != nil {
 				n.Config.Log.Error("failed to finalize main transaction", zap.Error(err))
 			} else {
@@ -276,10 +285,10 @@ func (n *Notary) PostPersist(bc blockchainer.Blockchainer, pool *mempool.Pool, b
 			}
 			continue
 		}
-		if r.minNotValidBefore <= bc.BlockHeight() { // then at least one of the fallbacks can already be sent.
+		if r.minNotValidBefore <= currHeight { // then at least one of the fallbacks can already be sent.
 			newFallbacks := r.fallbacks[:0]
 			for _, fb := range r.fallbacks {
-				if nvb := fb.GetAttributes(transaction.NotValidBeforeT)[0].Value.(*transaction.NotValidBefore).Height; nvb <= bc.BlockHeight() {
+				if nvb := fb.GetAttributes(transaction.NotValidBeforeT)[0].Value.(*transaction.NotValidBefore).Height; nvb <= currHeight {
 					if err := n.finalize(fb); err != nil {
 						newFallbacks = append(newFallbacks, fb) // wait for the next block to resend them
 					}