queue: add Blocking OperationMode

If Blocking mode is on PutBlock will block until there is enough space
in the queue.

Co-authored-by: Anna Shaleva <shaleva.ann@nspcc.ru>
Signed-off-by: Ekaterina Pavlova <ekt@morphbits.io>

pkg/network/bqueue/queue.go

@@ -3,6 +3,7 @@ package bqueue
 import (
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/nspcc-dev/neo-go/pkg/core/block"
 	"go.uber.org/zap"
@@ -15,6 +16,17 @@ type Blockqueuer interface {
 	BlockHeight() uint32
 }
 
+// OperationMode is the mode of operation for the block queue.
+// Could be either Blocking or NonBlocking.
+type OperationMode byte
+
+const (
+	// NonBlocking means that PutBlock will return immediately if the queue is full.
+	NonBlocking OperationMode = 0
+	// Blocking means that PutBlock will wait until there is enough space in the queue.
+	Blocking OperationMode = 1
+)
+
 // Queue is the block queue.
 type Queue struct {
 	log         *zap.Logger
@@ -28,6 +40,7 @@ type Queue struct {
 	len         int
 	lenUpdateF  func(int)
 	cacheSize   int
+	mode        OperationMode
 }
 
 // DefaultCacheSize is the default amount of blocks above the current height
@@ -39,7 +52,7 @@ func (bq *Queue) indexToPosition(i uint32) int {
 }
 
 // New creates an instance of BlockQueue.
-func New(bc Blockqueuer, log *zap.Logger, relayer func(*block.Block), cacheSize int, lenMetricsUpdater func(l int)) *Queue {
+func New(bc Blockqueuer, log *zap.Logger, relayer func(*block.Block), cacheSize int, lenMetricsUpdater func(l int), mode OperationMode) *Queue {
 	if log == nil {
 		return nil
 	}
@@ -55,6 +68,7 @@ func New(bc Blockqueuer, log *zap.Logger, relayer func(*block.Block), cacheSize
 		relayF:      relayer,
 		lenUpdateF:  lenMetricsUpdater,
 		cacheSize:   cacheSize,
+		mode:        mode,
 	}
 }
 
@@ -119,11 +133,32 @@ func (bq *Queue) PutBlock(block *block.Block) error {
 	if bq.discarded.Load() {
 		return nil
 	}
-	if block.Index <= h || h+uint32(bq.cacheSize) < block.Index {
-		// can easily happen when fetching the same blocks from
-		// different peers, thus not considered as error
+	// Can easily happen when fetching the same blocks from
+	// different peers, thus not considered as error.
+	if block.Index <= h {
 		return nil
 	}
+	if h+uint32(bq.cacheSize) < block.Index {
+		switch bq.mode {
+		case NonBlocking:
+			return nil
+		case Blocking:
+			bq.queueLock.Unlock()
+			t := time.NewTicker(time.Second)
+			defer t.Stop()
+			for range t.C {
+				if bq.discarded.Load() {
+					bq.queueLock.Lock()
+					return nil
+				}
+				h = bq.chain.BlockHeight()
+				if h+uint32(bq.cacheSize) >= block.Index {
+					bq.queueLock.Lock()
+					break
+				}
+			}
+		}
+	}
 	pos := bq.indexToPosition(block.Index)
 	// If we already have it, keep the old block, throw away the new one.
 	if bq.queue[pos] == nil || bq.queue[pos].Index < block.Index {

pkg/network/bqueue/queue_test.go

@@ -13,7 +13,7 @@ import (
 func TestBlockQueue(t *testing.T) {
 	chain := fakechain.NewFakeChain()
 	// notice, it's not yet running
-	bq := New(chain, zaptest.NewLogger(t), nil, 0, nil)
+	bq := New(chain, zaptest.NewLogger(t), nil, 0, nil, NonBlocking)
 	blocks := make([]*block.Block, 11)
 	for i := 1; i < 11; i++ {
 		blocks[i] = &block.Block{Header: block.Header{Index: uint32(i)}}

pkg/network/server.go

@@ -216,9 +216,9 @@ func newServerFromConstructors(config ServerConfig, chain Ledger, stSync StateSy
 	}
 	s.bQueue = bqueue.New(chain, log, func(b *block.Block) {
 		s.tryStartServices()
-	}, bqueue.DefaultCacheSize, updateBlockQueueLenMetric)
+	}, bqueue.DefaultCacheSize, updateBlockQueueLenMetric, bqueue.NonBlocking)
 
-	s.bSyncQueue = bqueue.New(s.stateSync, log, nil, bqueue.DefaultCacheSize, updateBlockQueueLenMetric)
+	s.bSyncQueue = bqueue.New(s.stateSync, log, nil, bqueue.DefaultCacheSize, updateBlockQueueLenMetric, bqueue.NonBlocking)
 
 	if s.MinPeers < 0 {
 		s.log.Info("bad MinPeers configured, using the default value",