path: root/core/chain_manager.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package core implements the Ethereum consensus protocol.
package core

import (
    "errors"
    "fmt"
    "io"
    "math/big"
    "sync"
    "sync/atomic"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/state"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/ethdb"
    "github.com/ethereum/go-ethereum/event"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/ethereum/go-ethereum/metrics"
    "github.com/ethereum/go-ethereum/pow"
    "github.com/ethereum/go-ethereum/rlp"
    "github.com/hashicorp/golang-lru"
)

var (
    chainlogger = logger.NewLogger("CHAIN")
    jsonlogger  = logger.NewJsonLogger()

    blockInsertTimer = metrics.NewTimer("chain/inserts")

    ErrNoGenesis = errors.New("Genesis not found in chain")
)

const (
    headerCacheLimit    = 512
    bodyCacheLimit      = 256
    tdCacheLimit        = 1024
    blockCacheLimit     = 256
    maxFutureBlocks     = 256
    maxTimeFutureBlocks = 30
    checkpointLimit     = 200
)

type ChainManager struct {
    //eth          EthManager
    chainDb      ethdb.Database
    processor    types.BlockProcessor
    eventMux     *event.TypeMux
    genesisBlock *types.Block
    // Last known total difficulty
    mu      sync.RWMutex
    chainmu sync.RWMutex
    tsmu    sync.RWMutex

    checkpoint      int // checkpoint counts towards the new checkpoint
    td              *big.Int
    currentBlock    *types.Block
    currentGasLimit *big.Int

    headerCache  *lru.Cache // Cache for the most recent block headers
    bodyCache    *lru.Cache // Cache for the most recent block bodies
    bodyRLPCache *lru.Cache // Cache for the most recent block bodies in RLP encoded format
    tdCache      *lru.Cache // Cache for the most recent block total difficulties
    blockCache   *lru.Cache // Cache for the most recent entire blocks
    futureBlocks *lru.Cache // future blocks are blocks added for later processing

    quit    chan struct{}
    running int32 // running must be called automically
    // procInterrupt must be atomically called
    procInterrupt int32 // interrupt signaler for block processing
    wg            sync.WaitGroup

    pow pow.PoW
}

func NewChainManager(chainDb ethdb.Database, pow pow.PoW, mux *event.TypeMux) (*ChainManager, error) {
    headerCache, _ := lru.New(headerCacheLimit)
    bodyCache, _ := lru.New(bodyCacheLimit)
    bodyRLPCache, _ := lru.New(bodyCacheLimit)
    tdCache, _ := lru.New(tdCacheLimit)
    blockCache, _ := lru.New(blockCacheLimit)
    futureBlocks, _ := lru.New(maxFutureBlocks)

    bc := &ChainManager{
        chainDb:      chainDb,
        eventMux:     mux,
        quit:         make(chan struct{}),
        headerCache:  headerCache,
        bodyCache:    bodyCache,
        bodyRLPCache: bodyRLPCache,
        tdCache:      tdCache,
        blockCache:   blockCache,
        futureBlocks: futureBlocks,
        pow:          pow,
    }

    bc.genesisBlock = bc.GetBlockByNumber(0)
    if bc.genesisBlock == nil {
        reader, err := NewDefaultGenesisReader()
        if err != nil {
            return nil, err
        }
        bc.genesisBlock, err = WriteGenesisBlock(chainDb, reader)
        if err != nil {
            return nil, err
        }
        glog.V(logger.Info).Infoln("WARNING: Wrote default ethereum genesis block")
    }
    if err := bc.setLastState(); err != nil {
        return nil, err
    }
    // Check the current state of the block hashes and make sure that we do not have any of the bad blocks in our chain
    for hash, _ := range BadHashes {
        if block := bc.GetBlock(hash); block != nil {
            glog.V(logger.Error).Infof("Found bad hash. Reorganising chain to state %x\n", block.ParentHash().Bytes()[:4])
            block = bc.GetBlock(block.ParentHash())
            if block == nil {
                glog.Fatal("Unable to complete. Parent block not found. Corrupted DB?")
            }
            bc.SetHead(block)

            glog.V(logger.Error).Infoln("Chain reorg was successfull. Resuming normal operation")
        }
    }
    // Take ownership of this particular state
    go bc.update()
    return bc, nil
}

func (bc *ChainManager) SetHead(head *types.Block) {
    bc.mu.Lock()
    defer bc.mu.Unlock()

    for block := bc.currentBlock; block != nil && block.Hash() != head.Hash(); block = bc.GetBlock(block.ParentHash()) {
        DeleteBlock(bc.chainDb, block.Hash())
    }
    bc.headerCache.Purge()
    bc.bodyCache.Purge()
    bc.bodyRLPCache.Purge()
    bc.blockCache.Purge()
    bc.futureBlocks.Purge()

    bc.currentBlock = head
    bc.setTotalDifficulty(bc.GetTd(head.Hash()))
    bc.insert(head)
    bc.setLastState()
}

func (self *ChainManager) Td() *big.Int {
    self.mu.RLock()
    defer self.mu.RUnlock()

    return new(big.Int).Set(self.td)
}

func (self *ChainManager) GasLimit() *big.Int {
    self.mu.RLock()
    defer self.mu.RUnlock()

    return self.currentBlock.GasLimit()
}

func (self *ChainManager) LastBlockHash() common.Hash {
    self.mu.RLock()
    defer self.mu.RUnlock()

    return self.currentBlock.Hash()
}

func (self *ChainManager) CurrentBlock() *types.Block {
    self.mu.RLock()
    defer self.mu.RUnlock()

    return self.currentBlock
}

func (self *ChainManager) Status() (td *big.Int, currentBlock common.Hash, genesisBlock common.Hash) {
    self.mu.RLock()
    defer self.mu.RUnlock()

    return new(big.Int).Set(self.td), self.currentBlock.Hash(), self.genesisBlock.Hash()
}

func (self *ChainManager) SetProcessor(proc types.BlockProcessor) {
    self.processor = proc
}

func (self *ChainManager) State() *state.StateDB {
    return state.New(self.CurrentBlock().Root(), self.chainDb)
}

func (bc *ChainManager) recover() bool {
    data, _ := bc.chainDb.Get([]byte("checkpoint"))
    if len(data) != 0 {
        block := bc.GetBlock(common.BytesToHash(data))
        if block != nil {
            if err := WriteCanonicalHash(bc.chainDb, block.Hash(), block.NumberU64()); err != nil {
                glog.Fatalf("failed to write database head number: %v", err)
            }
            if err := WriteHeadBlockHash(bc.chainDb, block.Hash()); err != nil {
                glog.Fatalf("failed to write database head hash: %v", err)
            }
            bc.currentBlock = block
            return true
        }
    }
    return false
}

func (bc *ChainManager) setLastState() error {
    head := GetHeadBlockHash(bc.chainDb)
    if head != (common.Hash{}) {
        block := bc.GetBlock(head)
        if block != nil {
            bc.currentBlock = block
        } else {
            glog.Infof("LastBlock (%x) not found. Recovering...\n", head)
            if bc.recover() {
                glog.Infof("Recover successful")
            } else {
                glog.Fatalf("Recover failed. Please report")
            }
        }
    } else {
        bc.Reset()
    }
    bc.td = bc.GetTd(bc.currentBlock.Hash())
    bc.currentGasLimit = CalcGasLimit(bc.currentBlock)

    if glog.V(logger.Info) {
        glog.Infof("Last block (#%v) %x TD=%v\n", bc.currentBlock.Number(), bc.currentBlock.Hash(), bc.td)
    }

    return nil
}

// Reset purges the entire blockchain, restoring it to its genesis state.
func (bc *ChainManager) Reset() {
    bc.ResetWithGenesisBlock(bc.genesisBlock)
}

// ResetWithGenesisBlock purges the entire blockchain, restoring it to the
// specified genesis state.
func (bc *ChainManager) ResetWithGenesisBlock(genesis *types.Block) {
    bc.mu.Lock()
    defer bc.mu.Unlock()

    // Dump the entire block chain and purge the caches
    for block := bc.currentBlock; block != nil; block = bc.GetBlock(block.ParentHash()) {
        DeleteBlock(bc.chainDb, block.Hash())
    }
    bc.headerCache.Purge()
    bc.bodyCache.Purge()
    bc.bodyRLPCache.Purge()
    bc.blockCache.Purge()
    bc.futureBlocks.Purge()

    // Prepare the genesis block and reinitialize the chain
    if err := WriteTd(bc.chainDb, genesis.Hash(), genesis.Difficulty()); err != nil {
        glog.Fatalf("failed to write genesis block TD: %v", err)
    }
    if err := WriteBlock(bc.chainDb, genesis); err != nil {
        glog.Fatalf("failed to write genesis block: %v", err)
    }
    bc.genesisBlock = genesis
    bc.insert(bc.genesisBlock)
    bc.currentBlock = bc.genesisBlock
    bc.setTotalDifficulty(genesis.Difficulty())
}

// Export writes the active chain to the given writer.
func (self *ChainManager) Export(w io.Writer) error {
    if err := self.ExportN(w, uint64(0), self.currentBlock.NumberU64()); err != nil {
        return err
    }
    return nil
}

// ExportN writes a subset of the active chain to the given writer.
func (self *ChainManager) ExportN(w io.Writer, first uint64, last uint64) error {
    self.mu.RLock()
    defer self.mu.RUnlock()

    if first > last {
        return fmt.Errorf("export failed: first (%d) is greater than last (%d)", first, last)
    }

    glog.V(logger.Info).Infof("exporting %d blocks...\n", last-first+1)

    for nr := first; nr <= last; nr++ {
        block := self.GetBlockByNumber(nr)
        if block == nil {
            return fmt.Errorf("export failed on #%d: not found", nr)
        }

        if err := block.EncodeRLP(w); err != nil {
            return err
        }
    }

    return nil
}

// insert injects a block into the current chain block chain. Note, this function
// assumes that the `mu` mutex is held!
func (bc *ChainManager) insert(block *types.Block) {
    // Add the block to the canonical chain number scheme and mark as the head
    if err := WriteCanonicalHash(bc.chainDb, block.Hash(), block.NumberU64()); err != nil {
        glog.Fatalf("failed to insert block number: %v", err)
    }
    if err := WriteHeadBlockHash(bc.chainDb, block.Hash()); err != nil {
        glog.Fatalf("failed to insert block number: %v", err)
    }
    // Add a new restore point if we reached some limit
    bc.checkpoint++
    if bc.checkpoint > checkpointLimit {
        if err := bc.chainDb.Put([]byte("checkpoint"), block.Hash().Bytes()); err != nil {
            glog.Fatalf("failed to create checkpoint: %v", err)
        }
        bc.checkpoint = 0
    }
    // Update the internal internal state with the head block
    bc.currentBlock = block
}

// Accessors
func (bc *ChainManager) Genesis() *types.Block {
    return bc.genesisBlock
}

// HasHeader checks if a block header is present in the database or not, caching
// it if present.
func (bc *ChainManager) HasHeader(hash common.Hash) bool {
    return bc.GetHeader(hash) != nil
}

// GetHeader retrieves a block header from the database by hash, caching it if
// found.
func (self *ChainManager) GetHeader(hash common.Hash) *types.Header {
    // Short circuit if the header's already in the cache, retrieve otherwise
    if header, ok := self.headerCache.Get(hash); ok {
        return header.(*types.Header)
    }
    header := GetHeader(self.chainDb, hash)
    if header == nil {
        return nil
    }
    // Cache the found header for next time and return
    self.headerCache.Add(header.Hash(), header)
    return header
}

// GetHeaderByNumber retrieves a block header from the database by number,
// caching it (associated with its hash) if found.
func (self *ChainManager) GetHeaderByNumber(number uint64) *types.Header {
    hash := GetCanonicalHash(self.chainDb, number)
    if hash == (common.Hash{}) {
        return nil
    }
    return self.GetHeader(hash)
}

// GetBody retrieves a block body (transactions and uncles) from the database by
// hash, caching it if found.
func (self *ChainManager) GetBody(hash common.Hash) *types.Body {
    // Short circuit if the body's already in the cache, retrieve otherwise
    if cached, ok := self.bodyCache.Get(hash); ok {
        body := cached.(*types.Body)
        return body
    }
    body := GetBody(self.chainDb, hash)
    if body == nil {
        return nil
    }
    // Cache the found body for next time and return
    self.bodyCache.Add(hash, body)
    return body
}

// GetBodyRLP retrieves a block body in RLP encoding from the database by hash,
// caching it if found.
func (self *ChainManager) GetBodyRLP(hash common.Hash) rlp.RawValue {
    // Short circuit if the body's already in the cache, retrieve otherwise
    if cached, ok := self.bodyRLPCache.Get(hash); ok {
        return cached.(rlp.RawValue)
    }
    body := GetBodyRLP(self.chainDb, hash)
    if len(body) == 0 {
        return nil
    }
    // Cache the found body for next time and return
    self.bodyRLPCache.Add(hash, body)
    return body
}

// GetTd retrieves a block's total difficulty in the canonical chain from the
// database by hash, caching it if found.
func (self *ChainManager) GetTd(hash common.Hash) *big.Int {
    // Short circuit if the td's already in the cache, retrieve otherwise
    if cached, ok := self.tdCache.Get(hash); ok {
        return cached.(*big.Int)
    }
    td := GetTd(self.chainDb, hash)
    if td == nil {
        return nil
    }
    // Cache the found body for next time and return
    self.tdCache.Add(hash, td)
    return td
}

// HasBlock checks if a block is fully present in the database or not, caching
// it if present.
func (bc *ChainManager) HasBlock(hash common.Hash) bool {
    return bc.GetBlock(hash) != nil
}

// GetBlock retrieves a block from the database by hash, caching it if found.
func (self *ChainManager) GetBlock(hash common.Hash) *types.Block {
    // Short circuit if the block's already in the cache, retrieve otherwise
    if block, ok := self.blockCache.Get(hash); ok {
        return block.(*types.Block)
    }
    block := GetBlock(self.chainDb, hash)
    if block == nil {
        return nil
    }
    // Cache the found block for next time and return
    self.blockCache.Add(block.Hash(), block)
    return block
}

// GetBlockByNumber retrieves a block from the database by number, caching it
// (associated with its hash) if found.
func (self *ChainManager) GetBlockByNumber(number uint64) *types.Block {
    hash := GetCanonicalHash(self.chainDb, number)
    if hash == (common.Hash{}) {
        return nil
    }
    return self.GetBlock(hash)
}

// GetBlockHashesFromHash retrieves a number of block hashes starting at a given
// hash, fetching towards the genesis block.
func (self *ChainManager) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {
    // Get the origin header from which to fetch
    header := self.GetHeader(hash)
    if header == nil {
        return nil
    }
    // Iterate the headers until enough is collected or the genesis reached
    chain := make([]common.Hash, 0, max)
    for i := uint64(0); i < max; i++ {
        if header = self.GetHeader(header.ParentHash); header == nil {
            break
        }
        chain = append(chain, header.Hash())
        if header.Number.Cmp(common.Big0) == 0 {
            break
        }
    }
    return chain
}

// [deprecated by eth/62]
// GetBlocksFromHash returns the block corresponding to hash and up to n-1 ancestors.
func (self *ChainManager) GetBlocksFromHash(hash common.Hash, n int) (blocks []*types.Block) {
    for i := 0; i < n; i++ {
        block := self.GetBlock(hash)
        if block == nil {
            break
        }
        blocks = append(blocks, block)
        hash = block.ParentHash()
    }
    return
}

func (self *ChainManager) GetUnclesInChain(block *types.Block, length int) (uncles []*types.Header) {
    for i := 0; block != nil && i < length; i++ {
        uncles = append(uncles, block.Uncles()...)
        block = self.GetBlock(block.ParentHash())
    }

    return
}

// setTotalDifficulty updates the TD of the chain manager. Note, this function
// assumes that the `mu` mutex is held!
func (bc *ChainManager) setTotalDifficulty(td *big.Int) {
    bc.td = new(big.Int).Set(td)
}

func (bc *ChainManager) Stop() {
    if !atomic.CompareAndSwapInt32(&bc.running, 0, 1) {
        return
    }
    close(bc.quit)
    atomic.StoreInt32(&bc.procInterrupt, 1)

    bc.wg.Wait()

    glog.V(logger.Info).Infoln("Chain manager stopped")
}

type queueEvent struct {
    queue          []interface{}
    canonicalCount int
    sideCount      int
    splitCount     int
}

func (self *ChainManager) procFutureBlocks() {
    blocks := make([]*types.Block, self.futureBlocks.Len())
    for i, hash := range self.futureBlocks.Keys() {
        block, _ := self.futureBlocks.Get(hash)
        blocks[i] = block.(*types.Block)
    }
    if len(blocks) > 0 {
        types.BlockBy(types.Number).Sort(blocks)
        self.InsertChain(blocks)
    }
}

type writeStatus byte

const (
    NonStatTy writeStatus = iota
    CanonStatTy
    SplitStatTy
    SideStatTy
)

// WriteBlock writes the block to the chain.
func (self *ChainManager) WriteBlock(block *types.Block) (status writeStatus, err error) {
    self.wg.Add(1)
    defer self.wg.Done()

    // Calculate the total difficulty of the block
    ptd := self.GetTd(block.ParentHash())
    if ptd == nil {
        return NonStatTy, ParentError(block.ParentHash())
    }
    td := new(big.Int).Add(block.Difficulty(), ptd)

    self.mu.RLock()
    cblock := self.currentBlock
    self.mu.RUnlock()

    // Compare the TD of the last known block in the canonical chain to make sure it's greater.
    // At this point it's possible that a different chain (fork) becomes the new canonical chain.
    if td.Cmp(self.Td()) > 0 {
        // chain fork
        if block.ParentHash() != cblock.Hash() {
            // during split we merge two different chains and create the new canonical chain
            err := self.reorg(cblock, block)
            if err != nil {
                return NonStatTy, err
            }
        }
        status = CanonStatTy

        self.mu.Lock()
        self.setTotalDifficulty(td)
        self.insert(block)
        self.mu.Unlock()
    } else {
        status = SideStatTy
    }

    if err := WriteTd(self.chainDb, block.Hash(), td); err != nil {
        glog.Fatalf("failed to write block total difficulty: %v", err)
    }
    if err := WriteBlock(self.chainDb, block); err != nil {
        glog.Fatalf("filed to write block contents: %v", err)
    }
    // Delete from future blocks
    self.futureBlocks.Remove(block.Hash())

    return
}

// InsertChain will attempt to insert the given chain in to the canonical chain or, otherwise, create a fork. It an error is returned
// it will return the index number of the failing block as well an error describing what went wrong (for possible errors see core/errors.go).
func (self *ChainManager) InsertChain(chain types.Blocks) (int, error) {
    self.wg.Add(1)
    defer self.wg.Done()

    self.chainmu.Lock()
    defer self.chainmu.Unlock()

    // A queued approach to delivering events. This is generally
    // faster than direct delivery and requires much less mutex
    // acquiring.
    var (
        queue      = make([]interface{}, len(chain))
        queueEvent = queueEvent{queue: queue}
        stats      struct{ queued, processed, ignored int }
        tstart     = time.Now()

        nonceChecked = make([]bool, len(chain))
    )

    // Start the parallel nonce verifier.
    nonceAbort, nonceResults := verifyNoncesFromBlocks(self.pow, chain)
    defer close(nonceAbort)

    txcount := 0
    for i, block := range chain {
        if atomic.LoadInt32(&self.procInterrupt) == 1 {
            glog.V(logger.Debug).Infoln("Premature abort during chain processing")
            break
        }

        bstart := time.Now()
        // Wait for block i's nonce to be verified before processing
        // its state transition.
        for !nonceChecked[i] {
            r := <-nonceResults
            nonceChecked[r.index] = true
            if !r.valid {
                block := chain[r.index]
                return r.index, &BlockNonceErr{Hash: block.Hash(), Number: block.Number(), Nonce: block.Nonce()}
            }
        }

        if BadHashes[block.Hash()] {
            err := fmt.Errorf("Found known bad hash in chain %x", block.Hash())
            blockErr(block, err)
            return i, err
        }
        // Call in to the block processor and check for errors. It's likely that if one block fails
        // all others will fail too (unless a known block is returned).
        logs, receipts, err := self.processor.Process(block)
        if err != nil {
            if IsKnownBlockErr(err) {
                stats.ignored++
                continue
            }

            if err == BlockFutureErr {
                // Allow up to MaxFuture second in the future blocks. If this limit
                // is exceeded the chain is discarded and processed at a later time
                // if given.
                max := big.NewInt(time.Now().Unix() + maxTimeFutureBlocks)
                if block.Time().Cmp(max) == 1 {
                    return i, fmt.Errorf("%v: BlockFutureErr, %v > %v", BlockFutureErr, block.Time(), max)
                }

                self.futureBlocks.Add(block.Hash(), block)
                stats.queued++
                continue
            }

            if IsParentErr(err) && self.futureBlocks.Contains(block.ParentHash()) {
                self.futureBlocks.Add(block.Hash(), block)
                stats.queued++
                continue
            }

            blockErr(block, err)

            go ReportBlock(block, err)

            return i, err
        }
        if err := PutBlockReceipts(self.chainDb, block, receipts); err != nil {
            glog.V(logger.Warn).Infoln("error writing block receipts:", err)
        }

        txcount += len(block.Transactions())
        // write the block to the chain and get the status
        status, err := self.WriteBlock(block)
        if err != nil {
            return i, err
        }
        switch status {
        case CanonStatTy:
            if glog.V(logger.Debug) {
                glog.Infof("[%v] inserted block #%d (%d TXs %v G %d UNCs) (%x...). Took %v\n", time.Now().UnixNano(), block.Number(), len(block.Transactions()), block.GasUsed(), len(block.Uncles()), block.Hash().Bytes()[0:4], time.Since(bstart))
            }
            queue[i] = ChainEvent{block, block.Hash(), logs}
            queueEvent.canonicalCount++

            // This puts transactions in a extra db for rpc
            PutTransactions(self.chainDb, block, block.Transactions())
            // store the receipts
            PutReceipts(self.chainDb, receipts)
        case SideStatTy:
            if glog.V(logger.Detail) {
                glog.Infof("inserted forked block #%d (TD=%v) (%d TXs %d UNCs) (%x...). Took %v\n", block.Number(), block.Difficulty(), len(block.Transactions()), len(block.Uncles()), block.Hash().Bytes()[0:4], time.Since(bstart))
            }
            queue[i] = ChainSideEvent{block, logs}
            queueEvent.sideCount++
        case SplitStatTy:
            queue[i] = ChainSplitEvent{block, logs}
            queueEvent.splitCount++
        }
        stats.processed++
    }

    if (stats.queued > 0 || stats.processed > 0 || stats.ignored > 0) && bool(glog.V(logger.Info)) {
        tend := time.Since(tstart)
        start, end := chain[0], chain[len(chain)-1]
        glog.Infof("imported %d block(s) (%d queued %d ignored) including %d txs in %v. #%v [%x / %x]\n", stats.processed, stats.queued, stats.ignored, txcount, tend, end.Number(), start.Hash().Bytes()[:4], end.Hash().Bytes()[:4])
    }

    go self.eventMux.Post(queueEvent)

    return 0, nil
}

// reorgs takes two blocks, an old chain and a new chain and will reconstruct the blocks and inserts them
// to be part of the new canonical chain and accumulates potential missing transactions and post an
// event about them
func (self *ChainManager) reorg(oldBlock, newBlock *types.Block) error {
    self.mu.Lock()
    defer self.mu.Unlock()

    var (
        newChain    types.Blocks
        commonBlock *types.Block
        oldStart    = oldBlock
        newStart    = newBlock
        deletedTxs  types.Transactions
    )

    // first reduce whoever is higher bound
    if oldBlock.NumberU64() > newBlock.NumberU64() {
        // reduce old chain
        for oldBlock = oldBlock; oldBlock != nil && oldBlock.NumberU64() != newBlock.NumberU64(); oldBlock = self.GetBlock(oldBlock.ParentHash()) {
            deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
        }
    } else {
        // reduce new chain and append new chain blocks for inserting later on
        for newBlock = newBlock; newBlock != nil && newBlock.NumberU64() != oldBlock.NumberU64(); newBlock = self.GetBlock(newBlock.ParentHash()) {
            newChain = append(newChain, newBlock)
        }
    }
    if oldBlock == nil {
        return fmt.Errorf("Invalid old chain")
    }
    if newBlock == nil {
        return fmt.Errorf("Invalid new chain")
    }

    numSplit := newBlock.Number()
    for {
        if oldBlock.Hash() == newBlock.Hash() {
            commonBlock = oldBlock
            break
        }
        newChain = append(newChain, newBlock)
        deletedTxs = append(deletedTxs, oldBlock.Transactions()...)

        oldBlock, newBlock = self.GetBlock(oldBlock.ParentHash()), self.GetBlock(newBlock.ParentHash())
        if oldBlock == nil {
            return fmt.Errorf("Invalid old chain")
        }
        if newBlock == nil {
            return fmt.Errorf("Invalid new chain")
        }
    }

    if glog.V(logger.Debug) {
        commonHash := commonBlock.Hash()
        glog.Infof("Chain split detected @ %x. Reorganising chain from #%v %x to %x", commonHash[:4], numSplit, oldStart.Hash().Bytes()[:4], newStart.Hash().Bytes()[:4])
    }

    var addedTxs types.Transactions
    // insert blocks. Order does not matter. Last block will be written in ImportChain itself which creates the new head properly
    for _, block := range newChain {
        // insert the block in the canonical way, re-writing history
        self.insert(block)
        // write canonical receipts and transactions
        PutTransactions(self.chainDb, block, block.Transactions())
        PutReceipts(self.chainDb, GetBlockReceipts(self.chainDb, block.Hash()))

        addedTxs = append(addedTxs, block.Transactions()...)
    }

    // calculate the difference between deleted and added transactions
    diff := types.TxDifference(deletedTxs, addedTxs)
    // When transactions get deleted from the database that means the
    // receipts that were created in the fork must also be deleted
    for _, tx := range diff {
        DeleteReceipt(self.chainDb, tx.Hash())
        DeleteTransaction(self.chainDb, tx.Hash())
    }
    self.eventMux.Post(RemovedTransactionEvent{diff})

    return nil
}

func (self *ChainManager) update() {
    events := self.eventMux.Subscribe(queueEvent{})
    futureTimer := time.Tick(5 * time.Second)
out:
    for {
        select {
        case ev := <-events.Chan():
            switch ev := ev.(type) {
            case queueEvent:
                for _, event := range ev.queue {
                    switch event := event.(type) {
                    case ChainEvent:
                        // We need some control over the mining operation. Acquiring locks and waiting for the miner to create new block takes too long
                        // and in most cases isn't even necessary.
                        if self.currentBlock.Hash() == event.Hash {
                            self.currentGasLimit = CalcGasLimit(event.Block)
                            self.eventMux.Post(ChainHeadEvent{event.Block})
                        }
                    }
                    self.eventMux.Post(event)
                }
            }
        case <-futureTimer:
            self.procFutureBlocks()
        case <-self.quit:
            break out
        }
    }
}

func blockErr(block *types.Block, err error) {
    h := block.Header()
    glog.V(logger.Error).Infof("Bad block #%v (%x)\n", h.Number, h.Hash().Bytes())
    glog.V(logger.Error).Infoln(err)
    glog.V(logger.Debug).Infoln(verifyNonces)
}