eth/downloader: fix expiration not running while fetching

eth/downloader/downloader.go

@@ -346,13 +346,28 @@ out:
 				d.peers.setState(blockPack.peerId, idleState)
 			}
 		case <-ticker.C:
-			// after removing bad peers make sure we actually have sufficient peer left to keep downloading
+			// Check for bad peers. Bad peers may indicate a peer not responding
+			// to a `getBlocks` message. A timeout of 5 seconds is set. Peers
+			// that badly or poorly behave are removed from the peer set (not banned).
+			// Bad peers are excluded from the available peer set and therefor won't be
+			// reused. XXX We could re-introduce peers after X time.
+			badPeers := d.queue.Expire(blockTtl)
+			for _, pid := range badPeers {
+				// XXX We could make use of a reputation system here ranking peers
+				// in their performance
+				// 1) Time for them to respond;
+				// 2) Measure their speed;
+				// 3) Amount and availability.
+				if peer := d.peers[pid]; peer != nil {
+					peer.demote()
+					peer.reset()
+				}
+			}
+			// After removing bad peers make sure we actually have sufficient peer left to keep downloading
 			if len(d.peers) == 0 {
 				d.queue.Reset()
-
 				return errNoPeers
 			}
-
 			// If there are unrequested hashes left start fetching
 			// from the available peers.
 			if d.queue.Pending() > 0 {
@@ -392,25 +407,6 @@ out:
 				// safely assume we're done. Another part of the process will  check
 				// for parent errors and will re-request anything that's missing
 				break out
-			} else {
-				// Check for bad peers. Bad peers may indicate a peer not responding
-				// to a `getBlocks` message. A timeout of 5 seconds is set. Peers
-				// that badly or poorly behave are removed from the peer set (not banned).
-				// Bad peers are excluded from the available peer set and therefor won't be
-				// reused. XXX We could re-introduce peers after X time.
-				badPeers := d.queue.Expire(blockTtl)
-				for _, pid := range badPeers {
-					// XXX We could make use of a reputation system here ranking peers
-					// in their performance
-					// 1) Time for them to respond;
-					// 2) Measure their speed;
-					// 3) Amount and availability.
-					if peer := d.peers[pid]; peer != nil {
-						peer.demote()
-						peer.reset()
-					}
-				}
-
 			}
 		}
 	}

eth/downloader/queue.go

@@ -12,7 +12,7 @@ import (
 )
 
 const (
-	blockCacheLimit = 4096 // Maximum number of blocks to cache before throttling the download
+	blockCacheLimit = 1024 // Maximum number of blocks to cache before throttling the download
 )
 
 // fetchRequest is a currently running block retrieval operation.
@@ -28,8 +28,7 @@ type queue struct {
 	hashQueue   *prque.Prque        // Priority queue of the block hashes to fetch
 	hashCounter int                 // Counter indexing the added hashes to ensure retrieval order
 
-	pendPool  map[string]*fetchRequest // Currently pending block retrieval operations
-	pendCount int                      // Number of pending block fetches (to throttle the download)
+	pendPool map[string]*fetchRequest // Currently pending block retrieval operations
 
 	blockPool   map[common.Hash]int // Hash-set of the downloaded data blocks, mapping to cache indexes
 	blockCache  []*types.Block      // Downloaded but not yet delivered blocks
@@ -58,7 +57,6 @@ func (q *queue) Reset() {
 	q.hashCounter = 0
 
 	q.pendPool = make(map[string]*fetchRequest)
-	q.pendCount = 0
 
 	q.blockPool = make(map[common.Hash]int)
 	q.blockOffset = 0
@@ -106,7 +104,13 @@ func (q *queue) Throttle() bool {
 	q.lock.RLock()
 	defer q.lock.RUnlock()
 
-	return q.pendCount >= len(q.blockCache)-len(q.blockPool)
+	// Calculate the currently in-flight block requests
+	pending := 0
+	for _, request := range q.pendPool {
+		pending += len(request.Hashes)
+	}
+	// Throttle if more blocks are in-flight than free space in the cache
+	return pending >= len(q.blockCache)-len(q.blockPool)
 }
 
 // Has checks if a hash is within the download queue or not.
@@ -206,10 +210,14 @@ func (q *queue) Reserve(p *peer, max int) *fetchRequest {
 	q.lock.Lock()
 	defer q.lock.Unlock()
 
-	// Short circuit if the pool has been depleted
+	// Short circuit if the pool has been depleted, or if the peer's already
+	// downloading something (sanity check not to corrupt state)
 	if q.hashQueue.Empty() {
 		return nil
 	}
+	if _, ok := q.pendPool[p.id]; ok {
+		return nil
+	}
 	// Retrieve a batch of hashes, skipping previously failed ones
 	send := make(map[common.Hash]int)
 	skip := make(map[common.Hash]int)
@@ -236,7 +244,6 @@ func (q *queue) Reserve(p *peer, max int) *fetchRequest {
 		Time:   time.Now(),
 	}
 	q.pendPool[p.id] = request
-	q.pendCount += len(request.Hashes)
 
 	return request
 }
@@ -250,7 +257,6 @@ func (q *queue) Cancel(request *fetchRequest) {
 		q.hashQueue.Push(hash, float32(index))
 	}
 	delete(q.pendPool, request.Peer.id)
-	q.pendCount -= len(request.Hashes)
 }
 
 // Expire checks for in flight requests that exceeded a timeout allowance,
@@ -266,7 +272,6 @@ func (q *queue) Expire(timeout time.Duration) []string {
 			for hash, index := range request.Hashes {
 				q.hashQueue.Push(hash, float32(index))
 			}
-			q.pendCount -= len(request.Hashes)
 			peers = append(peers, id)
 		}
 	}
@@ -289,9 +294,6 @@ func (q *queue) Deliver(id string, blocks []*types.Block) (err error) {
 	}
 	delete(q.pendPool, id)
 
-	// Mark all the hashes in the request as non-pending
-	q.pendCount -= len(request.Hashes)
-
 	// If no blocks were retrieved, mark them as unavailable for the origin peer
 	if len(blocks) == 0 {
 		for hash, _ := range request.Hashes {