eth/downloader: preallocate the block cache

eth/downloader/queue.go

@@ -50,10 +50,11 @@ type queue struct {
 // newQueue creates a new download queue for scheduling block retrieval.
 func newQueue() *queue {
 	return &queue{
-		hashPool:  make(map[common.Hash]int),
-		hashQueue: prque.New(),
-		pendPool:  make(map[string]*fetchRequest),
-		blockPool: make(map[common.Hash]int),
+		hashPool:   make(map[common.Hash]int),
+		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
-// offset, and a memory cap.
-func (q *queue) Alloc(offset int) {
+// Prepare configures the block cache offset to allow accepting inbound blocks.
+func (q *queue) Prepare(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))...)
-	}
 }