path: root/eth/sync.go

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.Tick(blockProcTimer)

    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:
            go pm.processBlocks()
        case <-pm.quitSync:
            return
        }
    }
}

// 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
    }

    // FIXME if we have the hash in our chain and the TD of the peer is
    // much higher than ours, something is wrong with us or the peer.
    // Check if the hash is on our own chain
    if pm.chainman.HasBlock(peer.recentHash) {
        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)
    }
}