eth/downloader: preallocate the block cache

eth/downloader/downloader.go

@@ -341,12 +341,12 @@ func (d *Downloader) fetchHashes(p *peer, h common.Hash) error {
 				active.getHashes(head)
 				continue
 			}
-			// We're done, allocate the download cache and proceed pulling the blocks
+			// We're done, prepare the download cache and proceed pulling the blocks
 			offset := 0
 			if block := d.getBlock(head); block != nil {
 				offset = int(block.NumberU64() + 1)
 			}
-			d.queue.Alloc(offset)
+			d.queue.Prepare(offset)
 			finished = true
 
 		case blockPack := <-d.blockCh:
@@ -504,7 +504,7 @@ out:
 					}
 					// Get a possible chunk. If nil is returned no chunk
 					// could be returned due to no hashes available.
-					request := d.queue.Reserve(peer)
+					request := d.queue.Reserve(peer, peer.Capacity())
 					if request == nil {
 						continue
 					}
@@ -551,7 +551,7 @@ func (d *Downloader) banBlocks(peerId string, head common.Hash) error {
 	if peer == nil {
 		return nil
 	}
-	request := d.queue.Reserve(peer)
+	request := d.queue.Reserve(peer, MaxBlockFetch)
 	if request == nil {
 		return nil
 	}

eth/downloader/downloader_test.go

@@ -186,7 +186,7 @@ func TestSynchronisation(t *testing.T) {
 	if err := tester.sync("peer", hashes[0]); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	if queued := len(tester.downloader.queue.blockCache); queued != targetBlocks {
+	if queued := len(tester.downloader.queue.blockPool); queued != targetBlocks {
 		t.Fatalf("synchronised block mismatch: have %v, want %v", queued, targetBlocks)
 	}
 }

eth/downloader/queue.go

@@ -54,6 +54,7 @@ func newQueue() *queue {
 		hashQueue:  prque.New(),
 		pendPool:   make(map[string]*fetchRequest),
 		blockPool:  make(map[common.Hash]int),
+		blockCache: make([]*Block, blockCacheLimit),
 	}
 }
 
@@ -70,7 +71,7 @@ func (q *queue) Reset() {
 
 	q.blockPool = make(map[common.Hash]int)
 	q.blockOffset = 0
-	q.blockCache = nil
+	q.blockCache = make([]*Block, blockCacheLimit)
 }
 
 // Size retrieves the number of hashes in the queue, returning separately for
@@ -208,7 +209,7 @@ func (q *queue) TakeBlocks() []*Block {
 
 // Reserve reserves a set of hashes for the given peer, skipping any previously
 // failed download.
-func (q *queue) Reserve(p *peer) *fetchRequest {
+func (q *queue) Reserve(p *peer, count int) *fetchRequest {
 	q.lock.Lock()
 	defer q.lock.Unlock()
 
@@ -345,20 +346,12 @@ func (q *queue) Deliver(id string, blocks []*types.Block) (err error) {
 	return nil
 }
 
-// Alloc ensures that the block cache is the correct size, given a starting
+// Prepare configures the block cache offset to allow accepting inbound blocks.
-// offset, and a memory cap.
+func (q *queue) Prepare(offset int) {
-func (q *queue) Alloc(offset int) {
 	q.lock.Lock()
 	defer q.lock.Unlock()
 
 	if q.blockOffset < offset {
 		q.blockOffset = offset
 	}
-	size := len(q.hashPool)
-	if size > blockCacheLimit {
-		size = blockCacheLimit
-	}
-	if len(q.blockCache) < size {
-		q.blockCache = append(q.blockCache, make([]*Block, size-len(q.blockCache))...)
-	}
 }