Only steal an odd request if the stealer more recently received a chunk

This helps break the stealing cycle during endgame, and lets us trickle the request to the peer conn with the best record. It might not be sufficient but works nice in testing so far.

diff --git a/requesting.go b/requesting.go
index fdf638fef80b2806f26ba97f742a4cb955b4cfa4..aaaa4f9cfc7d09b04656d5cb4882dcab96e9add2 100644 (file)
--- a/requesting.go
+++ b/requesting.go
@@ -231,7 +231,14 @@ func (p *Peer) applyRequestState(next desiredRequestState) bool {
                        continue
                }
                existing := t.requestingPeer(req)
-               if existing != nil && existing != p && existing.uncancelledRequests() > current.Requests.GetCardinality() {
+               if existing != nil && existing != p {
+                       // Don't steal from the poor.
+                       diff := int64(current.Requests.GetCardinality()) + 1 - (int64(existing.uncancelledRequests()) - 1)
+                       // Steal a request that leaves us with one more request than the existing peer
+                       // connection if the stealer more recently received a chunk.
+                       if diff > 1 || (diff == 1 && p.lastUsefulChunkReceived.Before(existing.lastUsefulChunkReceived)) {
+                               continue
+                       }
                        t.cancelRequest(req)
                }
                more = p.mustRequest(req)