eth, eth/downloader: Moved block processing & graceful shutdown

The downloader is no longer responsible for processing blocks. The
eth-protocol handler now takes care of this instead.

Added graceful shutdown during block processing. Closes #846

eth/sync.go

@@ -0,0 +1,101 @@
+package eth
+
+import (
+	"math"
+	"time"
+
+	"github.com/ethereum/go-ethereum/eth/downloader"
+	"github.com/ethereum/go-ethereum/logger"
+	"github.com/ethereum/go-ethereum/logger/glog"
+)
+
+// Sync contains all synchronisation code for the eth protocol
+
+func (pm *ProtocolManager) update() {
+	// itimer is used to determine when to start ignoring `minDesiredPeerCount`
+	itimer := time.NewTimer(peerCountTimeout)
+	// btimer is used for picking of blocks from the downloader
+	btimer := time.NewTicker(blockProcTimer)
+out:
+	for {
+		select {
+		case <-pm.newPeerCh:
+			// Meet the `minDesiredPeerCount` before we select our best peer
+			if len(pm.peers) < minDesiredPeerCount {
+				break
+			}
+
+			// Find the best peer
+			peer := getBestPeer(pm.peers)
+			if peer == nil {
+				glog.V(logger.Debug).Infoln("Sync attempt cancelled. No peers available")
+			}
+
+			itimer.Stop()
+			go pm.synchronise(peer)
+		case <-itimer.C:
+			// The timer will make sure that the downloader keeps an active state
+			// in which it attempts to always check the network for highest td peers
+			// Either select the peer or restart the timer if no peers could
+			// be selected.
+			if peer := getBestPeer(pm.peers); peer != nil {
+				go pm.synchronise(peer)
+			} else {
+				itimer.Reset(5 * time.Second)
+			}
+		case <-btimer.C:
+			go pm.processBlocks()
+		case <-pm.quitSync:
+			break out
+		}
+	}
+}
+
+// processBlocks will attempt to reconstruct a chain by checking the first item and check if it's
+// a known parent. The first block in the chain may be unknown during downloading. When the
+// downloader isn't downloading blocks will be dropped with an unknown parent until either it
+// has depleted the list or found a known parent.
+func (pm *ProtocolManager) processBlocks() error {
+	pm.wg.Add(1)
+	defer pm.wg.Done()
+
+	blocks := pm.downloader.TakeBlocks()
+	if len(blocks) == 0 {
+		return nil
+	}
+	defer pm.downloader.Done()
+
+	glog.V(logger.Debug).Infof("Inserting chain with %d blocks (#%v - #%v)\n", len(blocks), blocks[0].Number(), blocks[len(blocks)-1].Number())
+
+	for len(blocks) != 0 && !pm.quit {
+		max := int(math.Min(float64(len(blocks)), float64(blockProcAmount)))
+		_, err := pm.chainman.InsertChain(blocks[:max])
+		if err != nil {
+			return err
+		}
+		blocks = blocks[max:]
+	}
+	return nil
+}
+
+func (pm *ProtocolManager) synchronise(peer *peer) {
+	// Make sure the peer's TD is higher than our own. If not drop.
+	if peer.td.Cmp(pm.chainman.Td()) <= 0 {
+		return
+	}
+	// Check downloader if it's busy so it doesn't show the sync message
+	// for every attempty
+	if pm.downloader.IsBusy() {
+		return
+	}
+
+	// Get the hashes from the peer (synchronously)
+	err := pm.downloader.Synchronise(peer.id, peer.recentHash)
+	if err != nil && err == downloader.ErrBadPeer {
+		glog.V(logger.Debug).Infoln("removed peer from peer set due to bad action")
+		pm.removePeer(peer)
+	} else if err != nil {
+		// handle error
+		glog.V(logger.Detail).Infoln("error downloading:", err)
+	}
+}