path: root/eth/downloader/queue.go

// Copyright 2015 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/>.

// Contains the block download scheduler to collect download tasks and schedule
// them in an ordered, and throttled way.

package downloader

import (
    "errors"
    "fmt"
    "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/crypto"
    "github.com/ethereum/go-ethereum/ethdb"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/ethereum/go-ethereum/trie"
    "github.com/rcrowley/go-metrics"
    "gopkg.in/karalabe/cookiejar.v2/collections/prque"
)

var (
    blockCacheLimit = 1024 // Maximum number of blocks to cache before throttling the download
)

var (
    errNoFetchesPending = errors.New("no fetches pending")
    errStateSyncPending = errors.New("state trie sync already scheduled")
    errStaleDelivery    = errors.New("stale delivery")
)

// fetchRequest is a currently running data retrieval operation.
type fetchRequest struct {
    Peer    *peer               // Peer to which the request was sent
    Hashes  map[common.Hash]int // [eth/61] Requested hashes with their insertion index (priority)
    Headers []*types.Header     // [eth/62] Requested headers, sorted by request order
    Time    time.Time           // Time when the request was made
}

// fetchResult is a struct collecting partial results from data fetchers until
// all outstanding pieces complete and the result as a whole can be processed.
type fetchResult struct {
    Pending int // Number of data fetches still pending

    Header       *types.Header
    Uncles       []*types.Header
    Transactions types.Transactions
    Receipts     types.Receipts
}

// queue represents hashes that are either need fetching or are being fetched
type queue struct {
    mode          SyncMode // Synchronisation mode to decide on the block parts to schedule for fetching
    fastSyncPivot uint64   // Block number where the fast sync pivots into archive synchronisation mode

    hashPool    map[common.Hash]int // [eth/61] Pending hashes, mapping to their insertion index (priority)
    hashQueue   *prque.Prque        // [eth/61] Priority queue of the block hashes to fetch
    hashCounter int                 // [eth/61] Counter indexing the added hashes to ensure retrieval order

    headerHead common.Hash // [eth/62] Hash of the last queued header to verify order

    blockTaskPool  map[common.Hash]*types.Header // [eth/62] Pending block (body) retrieval tasks, mapping hashes to headers
    blockTaskQueue *prque.Prque                  // [eth/62] Priority queue of the headers to fetch the blocks (bodies) for
    blockPendPool  map[string]*fetchRequest      // [eth/62] Currently pending block (body) retrieval operations
    blockDonePool  map[common.Hash]struct{}      // [eth/62] Set of the completed block (body) fetches

    receiptTaskPool  map[common.Hash]*types.Header // [eth/63] Pending receipt retrieval tasks, mapping hashes to headers
    receiptTaskQueue *prque.Prque                  // [eth/63] Priority queue of the headers to fetch the receipts for
    receiptPendPool  map[string]*fetchRequest      // [eth/63] Currently pending receipt retrieval operations
    receiptDonePool  map[common.Hash]struct{}      // [eth/63] Set of the completed receipt fetches

    stateTaskIndex int                      // [eth/63] Counter indexing the added hashes to ensure prioritised retrieval order
    stateTaskPool  map[common.Hash]int      // [eth/63] Pending node data retrieval tasks, mapping to their priority
    stateTaskQueue *prque.Prque             // [eth/63] Priority queue of the hashes to fetch the node data for
    statePendPool  map[string]*fetchRequest // [eth/63] Currently pending node data retrieval operations

    stateDatabase   ethdb.Database   // [eth/63] Trie database to populate during state reassembly
    stateScheduler  *state.StateSync // [eth/63] State trie synchronisation scheduler and integrator
    stateProcessors int32            // [eth/63] Number of currently running state processors
    stateSchedLock  sync.RWMutex     // [eth/63] Lock serialising access to the state scheduler

    resultCache  []*fetchResult // Downloaded but not yet delivered fetch results
    resultOffset uint64         // Offset of the first cached fetch result in the block chain

    lock sync.RWMutex
}

// newQueue creates a new download queue for scheduling block retrieval.
func newQueue(stateDb ethdb.Database) *queue {
    return &queue{
        hashPool:         make(map[common.Hash]int),
        hashQueue:        prque.New(),
        blockTaskPool:    make(map[common.Hash]*types.Header),
        blockTaskQueue:   prque.New(),
        blockPendPool:    make(map[string]*fetchRequest),
        blockDonePool:    make(map[common.Hash]struct{}),
        receiptTaskPool:  make(map[common.Hash]*types.Header),
        receiptTaskQueue: prque.New(),
        receiptPendPool:  make(map[string]*fetchRequest),
        receiptDonePool:  make(map[common.Hash]struct{}),
        stateTaskPool:    make(map[common.Hash]int),
        stateTaskQueue:   prque.New(),
        statePendPool:    make(map[string]*fetchRequest),
        stateDatabase:    stateDb,
        resultCache:      make([]*fetchResult, blockCacheLimit),
    }
}

// Reset clears out the queue contents.
func (q *queue) Reset() {
    q.lock.Lock()
    defer q.lock.Unlock()

    q.stateSchedLock.Lock()
    defer q.stateSchedLock.Unlock()

    q.mode = FullSync
    q.fastSyncPivot = 0

    q.hashPool = make(map[common.Hash]int)
    q.hashQueue.Reset()
    q.hashCounter = 0

    q.headerHead = common.Hash{}

    q.blockTaskPool = make(map[common.Hash]*types.Header)
    q.blockTaskQueue.Reset()
    q.blockPendPool = make(map[string]*fetchRequest)
    q.blockDonePool = make(map[common.Hash]struct{})

    q.receiptTaskPool = make(map[common.Hash]*types.Header)
    q.receiptTaskQueue.Reset()
    q.receiptPendPool = make(map[string]*fetchRequest)
    q.receiptDonePool = make(map[common.Hash]struct{})

    q.stateTaskIndex = 0
    q.stateTaskPool = make(map[common.Hash]int)
    q.stateTaskQueue.Reset()
    q.statePendPool = make(map[string]*fetchRequest)
    q.stateScheduler = nil

    q.resultCache = make([]*fetchResult, blockCacheLimit)
    q.resultOffset = 0
}

// PendingBlocks retrieves the number of block (body) requests pending for retrieval.
func (q *queue) PendingBlocks() int {
    q.lock.RLock()
    defer q.lock.RUnlock()

    return q.hashQueue.Size() + q.blockTaskQueue.Size()
}

// PendingReceipts retrieves the number of block receipts pending for retrieval.
func (q *queue) PendingReceipts() int {
    q.lock.RLock()
    defer q.lock.RUnlock()

    return q.receiptTaskQueue.Size()
}

// PendingNodeData retrieves the number of node data entries pending for retrieval.
func (q *queue) PendingNodeData() int {
    q.stateSchedLock.RLock()
    defer q.stateSchedLock.RUnlock()

    if q.stateScheduler != nil {
        return q.stateScheduler.Pending()
    }
    return 0
}

// InFlightBlocks retrieves whether there are block fetch requests currently in
// flight.
func (q *queue) InFlightBlocks() bool {
    q.lock.RLock()
    defer q.lock.RUnlock()

    return len(q.blockPendPool) > 0
}

// InFlightReceipts retrieves whether there are receipt fetch requests currently
// in flight.
func (q *queue) InFlightReceipts() bool {
    q.lock.RLock()
    defer q.lock.RUnlock()

    return len(q.receiptPendPool) > 0
}

// InFlightNodeData retrieves whether there are node data entry fetch requests
// currently in flight.
func (q *queue) InFlightNodeData() bool {
    q.lock.RLock()
    defer q.lock.RUnlock()

    return len(q.statePendPool)+int(atomic.LoadInt32(&q.stateProcessors)) > 0
}

// Idle returns if the queue is fully idle or has some data still inside. This
// method is used by the tester to detect termination events.
func (q *queue) Idle() bool {
    q.lock.RLock()
    defer q.lock.RUnlock()

    queued := q.hashQueue.Size() + q.blockTaskQueue.Size() + q.receiptTaskQueue.Size() + q.stateTaskQueue.Size()
    pending := len(q.blockPendPool) + len(q.receiptPendPool) + len(q.statePendPool)
    cached := len(q.blockDonePool) + len(q.receiptDonePool)

    q.stateSchedLock.RLock()
    if q.stateScheduler != nil {
        queued += q.stateScheduler.Pending()
    }
    q.stateSchedLock.RUnlock()

    return (queued + pending + cached) == 0
}

// FastSyncPivot retrieves the currently used fast sync pivot point.
func (q *queue) FastSyncPivot() uint64 {
    q.lock.RLock()
    defer q.lock.RUnlock()

    return q.fastSyncPivot
}

// ShouldThrottleBlocks checks if the download should be throttled (active block (body)
// fetches exceed block cache).
func (q *queue) ShouldThrottleBlocks() bool {
    q.lock.RLock()
    defer q.lock.RUnlock()

    // Calculate the currently in-flight block (body) requests
    pending := 0
    for _, request := range q.blockPendPool {
        pending += len(request.Hashes) + len(request.Headers)
    }
    // Throttle if more blocks (bodies) are in-flight than free space in the cache
    return pending >= len(q.resultCache)-len(q.blockDonePool)
}

// ShouldThrottleReceipts checks if the download should be throttled (active receipt
// fetches exceed block cache).
func (q *queue) ShouldThrottleReceipts() bool {
    q.lock.RLock()
    defer q.lock.RUnlock()

    // Calculate the currently in-flight receipt requests
    pending := 0
    for _, request := range q.receiptPendPool {
        pending += len(request.Headers)
    }
    // Throttle if more receipts are in-flight than free space in the cache
    return pending >= len(q.resultCache)-len(q.receiptDonePool)
}

// Schedule61 adds a set of hashes for the download queue for scheduling, returning
// the new hashes encountered.
func (q *queue) Schedule61(hashes []common.Hash, fifo bool) []common.Hash {
    q.lock.Lock()
    defer q.lock.Unlock()

    // Insert all the hashes prioritised in the arrival order
    inserts := make([]common.Hash, 0, len(hashes))
    for _, hash := range hashes {
        // Skip anything we already have
        if old, ok := q.hashPool[hash]; ok {
            glog.V(logger.Warn).Infof("Hash %x already scheduled at index %v", hash, old)
            continue
        }
        // Update the counters and insert the hash
        q.hashCounter = q.hashCounter + 1
        inserts = append(inserts, hash)

        q.hashPool[hash] = q.hashCounter
        if fifo {
            q.hashQueue.Push(hash, -float32(q.hashCounter)) // Lowest gets schedules first
        } else {
            q.hashQueue.Push(hash, float32(q.hashCounter)) // Highest gets schedules first
        }
    }
    return inserts
}

// Schedule adds a set of headers for the download queue for scheduling, returning
// the new headers encountered.
func (q *queue) Schedule(headers []*types.Header, from uint64) []*types.Header {
    q.lock.Lock()
    defer q.lock.Unlock()

    // Insert all the headers prioritised by the contained block number
    inserts := make([]*types.Header, 0, len(headers))
    for _, header := range headers {
        // Make sure chain order is honoured and preserved throughout
        hash := header.Hash()
        if header.Number == nil || header.Number.Uint64() != from {
            glog.V(logger.Warn).Infof("Header #%v [%x] broke chain ordering, expected %d", header.Number, hash[:4], from)
            break
        }
        if q.headerHead != (common.Hash{}) && q.headerHead != header.ParentHash {
            glog.V(logger.Warn).Infof("Header #%v [%x] broke chain ancestry", header.Number, hash[:4])
            break
        }
        // Make sure no duplicate requests are executed
        if _, ok := q.blockTaskPool[hash]; ok {
            glog.V(logger.Warn).Infof("Header #%d [%x] already scheduled for block fetch", header.Number.Uint64(), hash[:4])
            continue
        }
        if _, ok := q.receiptTaskPool[hash]; ok {
            glog.V(logger.Warn).Infof("Header #%d [%x] already scheduled for receipt fetch", header.Number.Uint64(), hash[:4])
            continue
        }
        // Queue the header for content retrieval
        q.blockTaskPool[hash] = header
        q.blockTaskQueue.Push(header, -float32(header.Number.Uint64()))

        if q.mode == FastSync && header.Number.Uint64() <= q.fastSyncPivot {
            // Fast phase of the fast sync, retrieve receipts too
            q.receiptTaskPool[hash] = header
            q.receiptTaskQueue.Push(header, -float32(header.Number.Uint64()))
        }
        if q.mode == FastSync && header.Number.Uint64() == q.fastSyncPivot {
            // Pivoting point of the fast sync, retrieve the state tries
            q.stateSchedLock.Lock()
            q.stateScheduler = state.NewStateSync(header.Root, q.stateDatabase)
            q.stateSchedLock.Unlock()
        }
        inserts = append(inserts, header)
        q.headerHead = hash
        from++
    }
    return inserts
}

// GetHeadResult retrieves the first fetch result from the cache, or nil if it hasn't
// been downloaded yet (or simply non existent).
func (q *queue) GetHeadResult() *fetchResult {
    q.lock.RLock()
    defer q.lock.RUnlock()

    // If there are no results pending, return nil
    if len(q.resultCache) == 0 || q.resultCache[0] == nil {
        return nil
    }
    // If the next result is still incomplete, return nil
    if q.resultCache[0].Pending > 0 {
        return nil
    }
    // If the next result is the fast sync pivot...
    if q.mode == FastSync && q.resultCache[0].Header.Number.Uint64() == q.fastSyncPivot {
        // If the pivot state trie is still being pulled, return nil
        if len(q.stateTaskPool) > 0 {
            return nil
        }
        if q.PendingNodeData() > 0 {
            return nil
        }
        // If the state is done, but not enough post-pivot headers were verified, stall...
        for i := 0; i < fsHeaderForceVerify; i++ {
            if i+1 >= len(q.resultCache) || q.resultCache[i+1] == nil {
                return nil
            }
        }
    }
    return q.resultCache[0]
}

// TakeResults retrieves and permanently removes a batch of fetch results from
// the cache.
func (q *queue) TakeResults() []*fetchResult {
    q.lock.Lock()
    defer q.lock.Unlock()

    // Accumulate all available results
    results := []*fetchResult{}
    for i, result := range q.resultCache {
        // Stop if no more results are ready
        if result == nil || result.Pending > 0 {
            break
        }
        // The fast sync pivot block may only be processed after state fetch completes
        if q.mode == FastSync && result.Header.Number.Uint64() == q.fastSyncPivot {
            if len(q.stateTaskPool) > 0 {
                break
            }
            if q.PendingNodeData() > 0 {
                break
            }
            // Even is state fetch is done, ensure post-pivot headers passed verifications
            safe := true
            for j := 0; j < fsHeaderForceVerify; j++ {
                if i+j+1 >= len(q.resultCache) || q.resultCache[i+j+1] == nil {
                    safe = false
                }
            }
            if !safe {
                break
            }
        }
        // If we've just inserted the fast sync pivot, stop as the following batch needs different insertion
        if q.mode == FastSync && result.Header.Number.Uint64() == q.fastSyncPivot+1 && len(results) > 0 {
            break
        }
        results = append(results, result)

        hash := result.Header.Hash()
        delete(q.blockDonePool, hash)
        delete(q.receiptDonePool, hash)
    }
    // Delete the results from the slice and let them be garbage collected
    // without this slice trick the results would stay in memory until nil
    // would be assigned to them.
    copy(q.resultCache, q.resultCache[len(results):])
    for k, n := len(q.resultCache)-len(results), len(q.resultCache); k < n; k++ {
        q.resultCache[k] = nil
    }
    q.resultOffset += uint64(len(results))

    return results
}

// ReserveBlocks reserves a set of block hashes for the given peer, skipping any
// previously failed download.
func (q *queue) ReserveBlocks(p *peer, count int) *fetchRequest {
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.reserveHashes(p, count, q.hashQueue, nil, q.blockPendPool, len(q.resultCache)-len(q.blockDonePool))
}

// ReserveNodeData reserves a set of node data hashes for the given peer, skipping
// any previously failed download.
func (q *queue) ReserveNodeData(p *peer, count int) *fetchRequest {
    // Create a task generator to fetch status-fetch tasks if all schedules ones are done
    generator := func(max int) {
        q.stateSchedLock.Lock()
        defer q.stateSchedLock.Unlock()

        if q.stateScheduler != nil {
            for _, hash := range q.stateScheduler.Missing(max) {
                q.stateTaskPool[hash] = q.stateTaskIndex
                q.stateTaskQueue.Push(hash, -float32(q.stateTaskIndex))
                q.stateTaskIndex++
            }
        }
    }
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.reserveHashes(p, count, q.stateTaskQueue, generator, q.statePendPool, count)
}

// reserveHashes reserves a set of hashes for the given peer, skipping previously
// failed ones.
//
// Note, this method expects the queue lock to be already held for writing. The
// reason the lock is not obtained in here is because the parameters already need
// to access the queue, so they already need a lock anyway.
func (q *queue) reserveHashes(p *peer, count int, taskQueue *prque.Prque, taskGen func(int), pendPool map[string]*fetchRequest, maxPending int) *fetchRequest {
    // Short circuit if the peer's already downloading something (sanity check to
    // not corrupt state)
    if _, ok := pendPool[p.id]; ok {
        return nil
    }
    // Calculate an upper limit on the hashes we might fetch (i.e. throttling)
    allowance := maxPending
    if allowance > 0 {
        for _, request := range pendPool {
            allowance -= len(request.Hashes)
        }
    }
    // If there's a task generator, ask it to fill our task queue
    if taskGen != nil && taskQueue.Size() < allowance {
        taskGen(allowance - taskQueue.Size())
    }
    if taskQueue.Empty() {
        return nil
    }
    // Retrieve a batch of hashes, skipping previously failed ones
    send := make(map[common.Hash]int)
    skip := make(map[common.Hash]int)

    for proc := 0; (allowance == 0 || proc < allowance) && len(send) < count && !taskQueue.Empty(); proc++ {
        hash, priority := taskQueue.Pop()
        if p.ignored.Has(hash) {
            skip[hash.(common.Hash)] = int(priority)
        } else {
            send[hash.(common.Hash)] = int(priority)
        }
    }
    // Merge all the skipped hashes back
    for hash, index := range skip {
        taskQueue.Push(hash, float32(index))
    }
    // Assemble and return the block download request
    if len(send) == 0 {
        return nil
    }
    request := &fetchRequest{
        Peer:   p,
        Hashes: send,
        Time:   time.Now(),
    }
    pendPool[p.id] = request

    return request
}

// ReserveBodies reserves a set of body fetches for the given peer, skipping any
// previously failed downloads. Beside the next batch of needed fetches, it also
// returns a flag whether empty blocks were queued requiring processing.
func (q *queue) ReserveBodies(p *peer, count int) (*fetchRequest, bool, error) {
    isNoop := func(header *types.Header) bool {
        return header.TxHash == types.EmptyRootHash && header.UncleHash == types.EmptyUncleHash
    }
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.reserveHeaders(p, count, q.blockTaskPool, q.blockTaskQueue, q.blockPendPool, q.blockDonePool, isNoop)
}

// ReserveReceipts reserves a set of receipt fetches for the given peer, skipping
// any previously failed downloads. Beside the next batch of needed fetches, it
// also returns a flag whether empty receipts were queued requiring importing.
func (q *queue) ReserveReceipts(p *peer, count int) (*fetchRequest, bool, error) {
    isNoop := func(header *types.Header) bool {
        return header.ReceiptHash == types.EmptyRootHash
    }
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.reserveHeaders(p, count, q.receiptTaskPool, q.receiptTaskQueue, q.receiptPendPool, q.receiptDonePool, isNoop)
}

// reserveHeaders reserves a set of data download operations for a given peer,
// skipping any previously failed ones. This method is a generic version used
// by the individual special reservation functions.
//
// Note, this method expects the queue lock to be already held for writing. The
// reason the lock is not obtained in here is because the parameters already need
// to access the queue, so they already need a lock anyway.
func (q *queue) reserveHeaders(p *peer, count int, taskPool map[common.Hash]*types.Header, taskQueue *prque.Prque,
    pendPool map[string]*fetchRequest, donePool map[common.Hash]struct{}, isNoop func(*types.Header) bool) (*fetchRequest, bool, error) {
    // Short circuit if the pool has been depleted, or if the peer's already
    // downloading something (sanity check not to corrupt state)
    if taskQueue.Empty() {
        return nil, false, nil
    }
    if _, ok := pendPool[p.id]; ok {
        return nil, false, nil
    }
    // Calculate an upper limit on the items we might fetch (i.e. throttling)
    space := len(q.resultCache) - len(donePool)
    for _, request := range pendPool {
        space -= len(request.Headers)
    }
    // Retrieve a batch of tasks, skipping previously failed ones
    send := make([]*types.Header, 0, count)
    skip := make([]*types.Header, 0)

    progress := false
    for proc := 0; proc < space && len(send) < count && !taskQueue.Empty(); proc++ {
        header := taskQueue.PopItem().(*types.Header)

        // If we're the first to request this task, initialise the result container
        index := int(header.Number.Int64() - int64(q.resultOffset))
        if index >= len(q.resultCache) || index < 0 {
            return nil, false, errInvalidChain
        }
        if q.resultCache[index] == nil {
            components := 1
            if q.mode == FastSync && header.Number.Uint64() <= q.fastSyncPivot {
                components = 2
            }
            q.resultCache[index] = &fetchResult{
                Pending: components,
                Header:  header,
            }
        }
        // If this fetch task is a noop, skip this fetch operation
        if isNoop(header) {
            donePool[header.Hash()] = struct{}{}
            delete(taskPool, header.Hash())

            space, proc = space-1, proc-1
            q.resultCache[index].Pending--
            progress = true
            continue
        }
        // Otherwise unless the peer is known not to have the data, add to the retrieve list
        if p.ignored.Has(header.Hash()) {
            skip = append(skip, header)
        } else {
            send = append(send, header)
        }
    }
    // Merge all the skipped headers back
    for _, header := range skip {
        taskQueue.Push(header, -float32(header.Number.Uint64()))
    }
    // Assemble and return the block download request
    if len(send) == 0 {
        return nil, progress, nil
    }
    request := &fetchRequest{
        Peer:    p,
        Headers: send,
        Time:    time.Now(),
    }
    pendPool[p.id] = request

    return request, progress, nil
}

// CancelBlocks aborts a fetch request, returning all pending hashes to the queue.
func (q *queue) CancelBlocks(request *fetchRequest) {
    q.cancel(request, q.hashQueue, q.blockPendPool)
}

// CancelBodies aborts a body fetch request, returning all pending headers to the
// task queue.
func (q *queue) CancelBodies(request *fetchRequest) {
    q.cancel(request, q.blockTaskQueue, q.blockPendPool)
}

// CancelReceipts aborts a body fetch request, returning all pending headers to
// the task queue.
func (q *queue) CancelReceipts(request *fetchRequest) {
    q.cancel(request, q.receiptTaskQueue, q.receiptPendPool)
}

// CancelNodeData aborts a node state data fetch request, returning all pending
// hashes to the task queue.
func (q *queue) CancelNodeData(request *fetchRequest) {
    q.cancel(request, q.stateTaskQueue, q.statePendPool)
}

// Cancel aborts a fetch request, returning all pending hashes to the task queue.
func (q *queue) cancel(request *fetchRequest, taskQueue *prque.Prque, pendPool map[string]*fetchRequest) {
    q.lock.Lock()
    defer q.lock.Unlock()

    for hash, index := range request.Hashes {
        taskQueue.Push(hash, float32(index))
    }
    for _, header := range request.Headers {
        taskQueue.Push(header, -float32(header.Number.Uint64()))
    }
    delete(pendPool, request.Peer.id)
}

// Revoke cancels all pending requests belonging to a given peer. This method is
// meant to be called during a peer drop to quickly reassign owned data fetches
// to remaining nodes.
func (q *queue) Revoke(peerId string) {
    q.lock.Lock()
    defer q.lock.Unlock()

    if request, ok := q.blockPendPool[peerId]; ok {
        for hash, index := range request.Hashes {
            q.hashQueue.Push(hash, float32(index))
        }
        for _, header := range request.Headers {
            q.blockTaskQueue.Push(header, -float32(header.Number.Uint64()))
        }
        delete(q.blockPendPool, peerId)
    }
    if request, ok := q.receiptPendPool[peerId]; ok {
        for _, header := range request.Headers {
            q.receiptTaskQueue.Push(header, -float32(header.Number.Uint64()))
        }
        delete(q.receiptPendPool, peerId)
    }
    if request, ok := q.statePendPool[peerId]; ok {
        for hash, index := range request.Hashes {
            q.stateTaskQueue.Push(hash, float32(index))
        }
        delete(q.statePendPool, peerId)
    }
}

// ExpireBlocks checks for in flight requests that exceeded a timeout allowance,
// canceling them and returning the responsible peers for penalisation.
func (q *queue) ExpireBlocks(timeout time.Duration) []string {
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.expire(timeout, q.blockPendPool, q.hashQueue, blockTimeoutMeter)
}

// ExpireBodies checks for in flight block body requests that exceeded a timeout
// allowance, canceling them and returning the responsible peers for penalisation.
func (q *queue) ExpireBodies(timeout time.Duration) []string {
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.expire(timeout, q.blockPendPool, q.blockTaskQueue, bodyTimeoutMeter)
}

// ExpireReceipts checks for in flight receipt requests that exceeded a timeout
// allowance, canceling them and returning the responsible peers for penalisation.
func (q *queue) ExpireReceipts(timeout time.Duration) []string {
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.expire(timeout, q.receiptPendPool, q.receiptTaskQueue, receiptTimeoutMeter)
}

// ExpireNodeData checks for in flight node data requests that exceeded a timeout
// allowance, canceling them and returning the responsible peers for penalisation.
func (q *queue) ExpireNodeData(timeout time.Duration) []string {
    q.lock.Lock()
    defer q.lock.Unlock()

    return q.expire(timeout, q.statePendPool, q.stateTaskQueue, stateTimeoutMeter)
}

// expire is the generic check that move expired tasks from a pending pool back
// into a task pool, returning all entities caught with expired tasks.
//
// Note, this method expects the queue lock to be already held for writing. The
// reason the lock is not obtained in here is because the parameters already need
// to access the queue, so they already need a lock anyway.
func (q *queue) expire(timeout time.Duration, pendPool map[string]*fetchRequest, taskQueue *prque.Prque, timeoutMeter metrics.Meter) []string {
    // Iterate over the expired requests and return each to the queue
    peers := []string{}
    for id, request := range pendPool {
        if time.Since(request.Time) > timeout {
            // Update the metrics with the timeout
            timeoutMeter.Mark(1)

            // Return any non satisfied requests to the pool
            for hash, index := range request.Hashes {
                taskQueue.Push(hash, float32(index))
            }
            for _, header := range request.Headers {
                taskQueue.Push(header, -float32(header.Number.Uint64()))
            }
            peers = append(peers, id)
        }
    }
    // Remove the expired requests from the pending pool
    for _, id := range peers {
        delete(pendPool, id)
    }
    return peers
}

// DeliverBlocks injects a block retrieval response into the download queue.
func (q *queue) DeliverBlocks(id string, blocks []*types.Block) error {
    q.lock.Lock()
    defer q.lock.Unlock()

    // Short circuit if the blocks were never requested
    request := q.blockPendPool[id]
    if request == nil {
        return errNoFetchesPending
    }
    blockReqTimer.UpdateSince(request.Time)
    delete(q.blockPendPool, id)

    // If no blocks were retrieved, mark them as unavailable for the origin peer
    if len(blocks) == 0 {
        for hash, _ := range request.Hashes {
            request.Peer.ignored.Add(hash)
        }
    }
    // Iterate over the downloaded blocks and add each of them
    errs := make([]error, 0)
    for _, block := range blocks {
        // Skip any blocks that were not requested
        hash := block.Hash()
        if _, ok := request.Hashes[hash]; !ok {
            errs = append(errs, fmt.Errorf("non-requested block %x", hash))
            continue
        }
        // Reconstruct the next result if contents match up
        index := int(block.Number().Int64() - int64(q.resultOffset))
        if index >= len(q.resultCache) || index < 0 {
            errs = []error{errInvalidChain}
            break
        }
        q.resultCache[index] = &fetchResult{
            Header:       block.Header(),
            Transactions: block.Transactions(),
            Uncles:       block.Uncles(),
        }
        q.blockDonePool[block.Hash()] = struct{}{}

        delete(request.Hashes, hash)
        delete(q.hashPool, hash)
    }
    // Return all failed or missing fetches to the queue
    for hash, index := range request.Hashes {
        q.hashQueue.Push(hash, float32(index))
    }
    // If none of the blocks were good, it's a stale delivery
    switch {
    case len(errs) == 0:
        return nil

    case len(errs) == 1 && (errs[0] == errInvalidChain || errs[0] == errInvalidBlock):
        return errs[0]

    case len(errs) == len(blocks):
        return errStaleDelivery

    default:
        return fmt.Errorf("multiple failures: %v", errs)
    }
}

// DeliverBodies injects a block body retrieval response into the results queue.
func (q *queue) DeliverBodies(id string, txLists [][]*types.Transaction, uncleLists [][]*types.Header) error {
    q.lock.Lock()
    defer q.lock.Unlock()

    reconstruct := func(header *types.Header, index int, result *fetchResult) error {
        if types.DeriveSha(types.Transactions(txLists[index])) != header.TxHash || types.CalcUncleHash(uncleLists[index]) != header.UncleHash {
            return errInvalidBody
        }
        result.Transactions = txLists[index]
        result.Uncles = uncleLists[index]
        return nil
    }
    return q.deliver(id, q.blockTaskPool, q.blockTaskQueue, q.blockPendPool, q.blockDonePool, bodyReqTimer, len(txLists), reconstruct)
}

// DeliverReceipts injects a receipt retrieval response into the results queue.
func (q *queue) DeliverReceipts(id string, receiptList [][]*types.Receipt) error {
    q.lock.Lock()
    defer q.lock.Unlock()

    reconstruct := func(header *types.Header, index int, result *fetchResult) error {
        if types.DeriveSha(types.Receipts(receiptList[index])) != header.ReceiptHash {
            return errInvalidReceipt
        }
        result.Receipts = receiptList[index]
        return nil
    }
    return q.deliver(id, q.receiptTaskPool, q.receiptTaskQueue, q.receiptPendPool, q.receiptDonePool, receiptReqTimer, len(receiptList), reconstruct)
}

// deliver injects a data retrieval response into the results queue.
//
// Note, this method expects the queue lock to be already held for writing. The
// reason the lock is not obtained in here is because the parameters already need
// to access the queue, so they already need a lock anyway.
func (q *queue) deliver(id string, taskPool map[common.Hash]*types.Header, taskQueue *prque.Prque, pendPool map[string]*fetchRequest,
    donePool map[common.Hash]struct{}, reqTimer metrics.Timer, results int, reconstruct func(header *types.Header, index int, result *fetchResult) error) error {
    // Short circuit if the data was never requested
    request := pendPool[id]
    if request == nil {
        return errNoFetchesPending
    }
    reqTimer.UpdateSince(request.Time)
    delete(pendPool, id)

    // If no data items were retrieved, mark them as unavailable for the origin peer
    if results == 0 {
        for hash, _ := range request.Headers {
            request.Peer.ignored.Add(hash)
        }
    }
    // Assemble each of the results with their headers and retrieved data parts
    var (
        failure error
        useful  bool
    )
    for i, header := range request.Headers {
        // Short circuit assembly if no more fetch results are found
        if i >= results {
            break
        }
        // Reconstruct the next result if contents match up
        index := int(header.Number.Int64() - int64(q.resultOffset))
        if index >= len(q.resultCache) || index < 0 || q.resultCache[index] == nil {
            failure = errInvalidChain
            break
        }
        if err := reconstruct(header, i, q.resultCache[index]); err != nil {
            failure = err
            break
        }
        donePool[header.Hash()] = struct{}{}
        q.resultCache[index].Pending--
        useful = true

        // Clean up a successful fetch
        request.Headers[i] = nil
        delete(taskPool, header.Hash())
    }
    // Return all failed or missing fetches to the queue
    for _, header := range request.Headers {
        if header != nil {
            taskQueue.Push(header, -float32(header.Number.Uint64()))
        }
    }
    // If none of the data was good, it's a stale delivery
    switch {
    case failure == nil || failure == errInvalidChain:
        return failure

    case useful:
        return fmt.Errorf("partial failure: %v", failure)

    default:
        return errStaleDelivery
    }
}

// DeliverNodeData injects a node state data retrieval response into the queue.
func (q *queue) DeliverNodeData(id string, data [][]byte, callback func(error, int)) error {
    q.lock.Lock()
    defer q.lock.Unlock()

    // Short circuit if the data was never requested
    request := q.statePendPool[id]
    if request == nil {
        return errNoFetchesPending
    }
    stateReqTimer.UpdateSince(request.Time)
    delete(q.statePendPool, id)

    // If no data was retrieved, mark their hashes as unavailable for the origin peer
    if len(data) == 0 {
        for hash, _ := range request.Hashes {
            request.Peer.ignored.Add(hash)
        }
    }
    // Iterate over the downloaded data and verify each of them
    errs := make([]error, 0)
    process := []trie.SyncResult{}
    for _, blob := range data {
        // Skip any blocks that were not requested
        hash := common.BytesToHash(crypto.Sha3(blob))
        if _, ok := request.Hashes[hash]; !ok {
            errs = append(errs, fmt.Errorf("non-requested state data %x", hash))
            continue
        }
        // Inject the next state trie item into the processing queue
        process = append(process, trie.SyncResult{hash, blob})

        delete(request.Hashes, hash)
        delete(q.stateTaskPool, hash)
    }
    // Start the asynchronous node state data injection
    atomic.AddInt32(&q.stateProcessors, 1)
    go func() {
        defer atomic.AddInt32(&q.stateProcessors, -1)
        q.deliverNodeData(process, callback)
    }()
    // Return all failed or missing fetches to the queue
    for hash, index := range request.Hashes {
        q.stateTaskQueue.Push(hash, float32(index))
    }
    // If none of the data items were good, it's a stale delivery
    switch {
    case len(errs) == 0:
        return nil

    case len(errs) == len(request.Hashes):
        return errStaleDelivery

    default:
        return fmt.Errorf("multiple failures: %v", errs)
    }
}

// deliverNodeData is the asynchronous node data processor that injects a batch
// of sync results into the state scheduler.
func (q *queue) deliverNodeData(results []trie.SyncResult, callback func(error, int)) {
    // Process results one by one to permit task fetches in between
    for i, result := range results {
        q.stateSchedLock.Lock()

        if q.stateScheduler == nil {
            // Syncing aborted since this async delivery started, bail out
            q.stateSchedLock.Unlock()
            callback(errNoFetchesPending, i)
            return
        }
        if _, err := q.stateScheduler.Process([]trie.SyncResult{result}); err != nil {
            // Processing a state result failed, bail out
            q.stateSchedLock.Unlock()
            callback(err, i)
            return
        }
        // Item processing succeeded, release the lock (temporarily)
        q.stateSchedLock.Unlock()
    }
    callback(nil, len(results))
}

// Prepare configures the result cache to allow accepting and caching inbound
// fetch results.
func (q *queue) Prepare(offset uint64, mode SyncMode, pivot uint64) {
    q.lock.Lock()
    defer q.lock.Unlock()

    if q.resultOffset < offset {
        q.resultOffset = offset
    }
    q.fastSyncPivot = pivot
    q.mode = mode
}