[release/1.4.6] eth/downloader: stream partial skeleton filling to processor

(cherry picked from commit e86619e75d)

eth/downloader/queue.go

@@ -87,6 +87,7 @@ type queue struct {
 	headerPendPool  map[string]*fetchRequest       // [eth/62] Currently pending header retrieval operations
 	headerDonePool  map[uint64]struct{}            // [eth/62] Set of the completed header fetches
 	headerResults   []*types.Header                // [eth/62] Result cache accumulating the completed headers
+	headerProced    int                            // [eth/62] Number of headers already processed from the results
 	headerOffset    uint64                         // [eth/62] Number of the first header in the result cache
 	headerContCh    chan bool                      // [eth/62] Channel to notify when header download finishes
 
@@ -365,6 +366,7 @@ func (q *queue) ScheduleSkeleton(from uint64, skeleton []*types.Header) {
 	q.headerTaskQueue = prque.New()
 	q.headerPeerMiss = make(map[string]map[uint64]struct{}) // Reset availability to correct invalid chains
 	q.headerResults = make([]*types.Header, len(skeleton)*MaxHeaderFetch)
+	q.headerProced = 0
 	q.headerOffset = from
 	q.headerContCh = make(chan bool, 1)
 
@@ -378,14 +380,14 @@ func (q *queue) ScheduleSkeleton(from uint64, skeleton []*types.Header) {
 
 // RetrieveHeaders retrieves the header chain assemble based on the scheduled
 // skeleton.
-func (q *queue) RetrieveHeaders() []*types.Header {
+func (q *queue) RetrieveHeaders() ([]*types.Header, int) {
 	q.lock.Lock()
 	defer q.lock.Unlock()
 
-	headers := q.headerResults
-	q.headerResults = nil
+	headers, proced := q.headerResults, q.headerProced
+	q.headerResults, q.headerProced = nil, 0
 
-	return headers
+	return headers, proced
 }
 
 // Schedule adds a set of headers for the download queue for scheduling, returning
@@ -976,7 +978,11 @@ func (q *queue) DeliverBlocks(id string, blocks []*types.Block) (int, error) {
 // DeliverHeaders injects a header retrieval response into the header results
 // cache. This method either accepts all headers it received, or none of them
 // if they do not map correctly to the skeleton.
-func (q *queue) DeliverHeaders(id string, headers []*types.Header) (int, error) {
+//
+// If the headers are accepted, the method makes an attempt to deliver the set
+// of ready headers to the processor to keep the pipeline full. However it will
+// not block to prevent stalling other pending deliveries.
+func (q *queue) DeliverHeaders(id string, headers []*types.Header, headerProcCh chan []*types.Header) (int, error) {
 	q.lock.Lock()
 	defer q.lock.Unlock()
 
@@ -1030,10 +1036,27 @@ func (q *queue) DeliverHeaders(id string, headers []*types.Header) (int, error)
 		q.headerTaskQueue.Push(request.From, -float32(request.From))
 		return 0, errors.New("delivery not accepted")
 	}
-	// Clean up a successful fetch, check for termination and return
+	// Clean up a successful fetch and try to deliver any sub-results
 	copy(q.headerResults[request.From-q.headerOffset:], headers)
 	delete(q.headerTaskPool, request.From)
 
+	ready := 0
+	for q.headerProced+ready < len(q.headerResults) && q.headerResults[q.headerProced+ready] != nil {
+		ready += MaxHeaderFetch
+	}
+	if ready > 0 {
+		// Headers are ready for delivery, gather them and push forward (non blocking)
+		process := make([]*types.Header, ready)
+		copy(process, q.headerResults[q.headerProced:q.headerProced+ready])
+
+		select {
+		case headerProcCh <- process:
+			glog.V(logger.Detail).Infof("%s: pre-scheduled %d headers from #%v", id, len(process), process[0].Number)
+			q.headerProced += len(process)
+		default:
+		}
+	}
+	// Check for termination and return
 	if len(q.headerTaskPool) == 0 {
 		q.headerContCh <- false
 	}