// Contains the block download scheduler to collect download tasks and schedule
// them in an ordered, and throttled way.
package downloader
import (
"errors"
"fmt"
"sync"
"time"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
"gopkg.in/karalabe/cookiejar.v2/collections/prque"
)
var (
blockCacheLimit = 8 * MaxBlockFetch // Maximum number of blocks to cache before throttling the download
)
var (
errNoFetchesPending = errors.New("no fetches pending")
errStaleDelivery = errors.New("stale delivery")
)
// fetchRequest is a currently running block retrieval operation.
type fetchRequest struct {
Peer *peer // Peer to which the request was sent
Hashes map[common.Hash]int // Requested hashes with their insertion index (priority)
Time time.Time // Time when the request was made
}
// queue represents hashes that are either need fetching or are being fetched
type queue struct {
hashPool map[common.Hash]int // Pending hashes, mapping to their insertion index (priority)
hashQueue *prque.Prque // Priority queue of the block hashes to fetch
hashCounter int // Counter indexing the added hashes to ensure retrieval order
pendPool map[string]*fetchRequest // Currently pending block retrieval operations
blockPool map[common.Hash]int // Hash-set of the downloaded data blocks, mapping to cache indexes
blockCache []*Block // Downloaded but not yet delivered blocks
blockOffset int // Offset of the first cached block in the block-chain
lock sync.RWMutex
}
// newQueue creates a new download queue for scheduling block retrieval.
func newQueue() *queue {
return &queue{
hashPool: make(map[common.Hash]int),
hashQueue: prque.New(),
pendPool: make(map[string]*fetchRequest),
blockPool: make(map[common.Hash]int),
blockCache: make([]*Block, blockCacheLimit),
}
}
// Reset clears out the queue contents.
func (q *queue) Reset() {
q.lock.Lock()
defer q.lock.Unlock()
q.hashPool = make(map[common.Hash]int)
q.hashQueue.Reset()
q.hashCounter = 0
q.pendPool = make(map[string]*fetchRequest)
q.blockPool = make(map[common.Hash]int)
q.blockOffset = 0
q.blockCache = make([]*Block, blockCacheLimit)
}
// Size retrieves the number of hashes in the queue, returning separately for
// pending and already downloaded.
func (q *queue) Size() (int, int) {
q.lock.RLock()
defer q.lock.RUnlock()
return len(q.hashPool), len(q.blockPool)
}
// Pending retrieves the number of hashes pending for retrieval.
func (q *queue) Pending() int {
q.lock.RLock()
defer q.lock.RUnlock()
return q.hashQueue.Size()
}
// InFlight retrieves the number of fetch requests currently in flight.
func (q *queue) InFlight() int {
q.lock.RLock()
defer q.lock.RUnlock()
return len(q.pendPool)
}
// Throttle checks if the download should be throttled (active block fetches
// exceed block cache).
func (q *queue) Throttle() bool {
q.lock.RLock()
defer q.lock.RUnlock()
// Calculate the currently in-flight block requests
pending := 0
for _, request := range q.pendPool {
pending += len(request.Hashes)
}
// Throttle if more blocks are in-flight than free space in the cache
return pending >= len(q.blockCache)-len(q.blockPool)
}
// Has checks if a hash is within the download queue or not.
func (q *queue) Has(hash common.Hash) bool {
q.lock.RLock()
defer q.lock.RUnlock()
if _, ok := q.hashPool[hash]; ok {
return true
}
if _, ok := q.blockPool[hash]; ok {
return true
}
return false
}
// Insert adds a set of hashes for the download queue for scheduling, returning
// the new hashes encountered.
func (q *queue) Insert(hashes []common.Hash) []common.Hash {
q.lock.Lock()
defer q.lock.Unlock()
// Insert all the hashes prioritized 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
q.hashQueue.Push(hash, float32(q.hashCounter)) // Highest gets schedules first
}
return inserts
}
// GetHeadBlock retrieves the first block from the cache, or nil if it hasn't
// been downloaded yet (or simply non existent).
func (q *queue) GetHeadBlock() *Block {
q.lock.RLock()
defer q.lock.RUnlock()
if len(q.blockCache) == 0 {
return nil
}
return q.blockCache[0]
}
// GetBlock retrieves a downloaded block, or nil if non-existent.
func (q *queue) GetBlock(hash common.Hash) *Block {
q.lock.RLock()
defer q.lock.RUnlock()
// Short circuit if the block hasn't been downloaded yet
index, ok := q.blockPool[hash]
if !ok {
return nil
}
// Return the block if it's still available in the cache
if q.blockOffset <= index && index < q.blockOffset+len(q.blockCache) {
return q.blockCache[index-q.blockOffset]
}
return nil
}
// TakeBlocks retrieves and permanently removes a batch of blocks from the cache.
func (q *queue) TakeBlocks() []*Block {
q.lock.Lock()
defer q.lock.Unlock()
// Accumulate all available blocks
blocks := []*Block{}
for _, block := range q.blockCache {
if block == nil {
break
}
blocks = append(blocks, block)
delete(q.blockPool, block.RawBlock.Hash())
}
// Delete the blocks from the slice and let them be garbage collected
// without this slice trick the blocks would stay in memory until nil
// would be assigned to q.blocks
copy(q.blockCache, q.blockCache[len(blocks):])
for k, n := len(q.blockCache)-len(blocks), len(q.blockCache); k < n; k++ {
q.blockCache[k] = nil
}
q.blockOffset += len(blocks)
return blocks
}
// Reserve reserves a set of hashes for the given peer, skipping any previously
// failed download.
func (q *queue) Reserve(p *peer, count int) *fetchRequest {
q.lock.Lock()
defer q.lock.Unlock()
// Short circuit if the pool has been depleted, or if the peer's already
// downloading something (sanity check not to corrupt state)
if q.hashQueue.Empty() {
return nil
}
if _, ok := q.pendPool[p.id]; ok {
return nil
}
// Calculate an upper limit on the hashes we might fetch (i.e. throttling)
space := len(q.blockCache) - len(q.blockPool)
for _, request := range q.pendPool {
space -= len(request.Hashes)
}
// Retrieve a batch of hashes, skipping previously failed ones
send := make(map[common.Hash]int)
skip := make(map[common.Hash]int)
for proc := 0; proc < space && len(send) < count && !q.hashQueue.Empty(); proc++ {
hash, priority := q.hashQueue.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 {
q.hashQueue.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(),
}
q.pendPool[p.id] = request
return request
}
// Cancel aborts a fetch request, returning all pending hashes to the queue.
func (q *queue) Cancel(request *fetchRequest) {
q.lock.Lock()
defer q.lock.Unlock()
for hash, index := range request.Hashes {
q.hashQueue.Push(hash, float32(index))
}
delete(q.pendPool, request.Peer.id)
}
// Expire checks for in flight requests that exceeded a timeout allowance,
// canceling them and returning the responsible peers for penalization.
func (q *queue) Expire(timeout time.Duration) []string {
q.lock.Lock()
defer q.lock.Unlock()
// Iterate over the expired requests and return each to the queue
peers := []string{}
for id, request := range q.pendPool {
if time.Since(request.Time) > timeout {
for hash, index := range request.Hashes {
q.hashQueue.Push(hash, float32(index))
}
peers = append(peers, id)
}
}
// Remove the expired requests from the pending pool
for _, id := range peers {
delete(q.pendPool, id)
}
return peers
}
// Deliver injects a block retrieval response into the download queue.
func (q *queue) Deliver(id string, blocks []*types.Block) (err error) {
q.lock.Lock()
defer q.lock.Unlock()
// Short circuit if the blocks were never requested
request := q.pendPool[id]
if request == nil {
return errNoFetchesPending
}
delete(q.pendPool, 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
}
// If a requested block falls out of the range, the hash chain is invalid
index := int(block.NumberU64()) - q.blockOffset
if index >= len(q.blockCache) || index < 0 {
return ErrInvalidChain
}
// Otherwise merge the block and mark the hash block
q.blockCache[index] = &Block{
RawBlock: block,
OriginPeer: id,
}
delete(request.Hashes, hash)
delete(q.hashPool, hash)
q.blockPool[hash] = int(block.NumberU64())
}
// 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
if len(errs) != 0 {
if len(errs) == len(blocks) {
return errStaleDelivery
}
return fmt.Errorf("multiple failures: %v", errs)
}
return nil
}
// Prepare configures the block cache offset to allow accepting inbound blocks.
func (q *queue) Prepare(offset int) {
q.lock.Lock()
defer q.lock.Unlock()
if q.blockOffset < offset {
q.blockOffset = offset
}
}
