Reduce redunant payload creation (ethereum#44)

* Remove redundant payload creation

* pr comments

miner/multi_worker.go

@@ -113,23 +113,27 @@ func (w *multiWorker) buildPayload(args *BuildPayloadArgs) (*Payload, error) {
 	// Construct a payload object for return.
 	payload := newPayload(empty, args.Id())
 
+	if len(w.workers) == 0 {
+		return payload, nil
+	}
+
 	// Keep separate payloads for each worker so that ResolveFull actually resolves the best of all workers
 	workerPayloads := []*Payload{}
 
-	for _, worker := range w.workers {
+	for _, w := range w.workers {
 		workerPayload := newPayload(empty, args.Id())
 		workerPayloads = append(workerPayloads, workerPayload)
-		go func() {
-			// Update routine done elsewhere!
 
+		go func(w *worker) {
+			// Update routine done elsewhere!
 			start := time.Now()
-			block, fees, err := worker.getSealingBlock(args.Parent, args.Timestamp, args.FeeRecipient, args.GasLimit, args.Random, args.Withdrawals, false, args.BlockHook)
+			block, fees, err := w.getSealingBlock(args.Parent, args.Timestamp, args.FeeRecipient, args.GasLimit, args.Random, args.Withdrawals, false, args.BlockHook)
 			if err == nil {
 				workerPayload.update(block, fees, time.Since(start))
 			}
-		}()
+		}(w)
 	}
-
+	
 	go payload.resolveBestFullPayload(workerPayloads)
 
 	return payload, nil

miner/payload_building.go

@@ -79,7 +79,7 @@ func newPayload(empty *types.Block, id engine.PayloadID) *Payload {
 		empty: empty,
 		stop:  make(chan struct{}),
 	}
-	log.Info("Starting work on payload", "id", payload.id)
+
 	payload.cond = sync.NewCond(&payload.lock)
 	return payload
 }
@@ -113,7 +113,7 @@ func (payload *Payload) resolveBestFullPayload(payloads []*Payload) {
 	payload.lock.Lock()
 	defer payload.lock.Unlock()
 
-	log.Info("XXX resolving")
+	log.Trace("resolving best payload")
 	for _, p := range payloads {
 		p.lock.Lock()
 
@@ -132,15 +132,15 @@ func (payload *Payload) resolveBestFullPayload(payloads []*Payload) {
 			}
 
 			if payload.full == nil || payload.fullFees.Cmp(p.fullFees) < 0 {
-				log.Info("XXX updated")
+				log.Trace("best payload updated", "id", p.id, "blockHash", p.full.Hash())
 				payload.full = p.full
 				payload.fullFees = p.fullFees
 			}
 			p.lock.Unlock()
 		}
 	}
 
-	log.Info("XXX resolved")
+	log.Trace("best payload resolved", "id", payload.id, "blockHash", payload.full.Hash())
 	payload.cond.Broadcast() // fire signal for notifying full block
 }