// 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"
)
const (
blockCacheLimit = 1024 // Maximum number of blocks to cache before throttling the download
)
// 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 []*types.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),
}
}
// 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 = nil
}
// 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.
func (q *queue) Insert(hashes []common.Hash) {
q.lock.Lock()
defer q.lock.Unlock()
// Insert all the hashes prioritized in the arrival order
for i, hash := range hashes {
index := q.hashCounter + i
if old, ok := q.hashPool[hash]; ok {
glog.V(logger.Warn).Infof("Hash %x already scheduled at index %v", hash, old)
continue
}
q.hashPool[hash] = index
q.hashQueue.Push(hash, float32(index)) // Highest gets schedules first
}
// Update the hash counter for the next batch of inserts
q.hashCounter += len(hashes)
}
// 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() *types.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) *types.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.
// The head parameter is required to prevent a race condition where concurrent
// takes may fail parent verifications.
func (q *queue) TakeBlocks(head *types.Block) types.Blocks {
q.lock.Lock()
defer q.lock.Unlock()
// Short circuit if the head block's different
if len(q.blockCache) == 0 || q.blockCache[0] != head {
return nil
}
// Otherwise accumulate all available blocks
var blocks types.Blocks
for _, block := range q.blockCache {
if block == nil {
break
}
blocks = append(blocks, block)
delete(q.blockPool, block.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, max 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
}
// Retrieve a batch of hashes, skipping previously failed ones
send := make(map[common.Hash]int)
skip := make(map[common.Hash]int)
for len(send) < max && !q.hashQueue.Empty() {
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 errors.New("no fetches pending")
}
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 fall outside the cache range
index := int(block.NumberU64()) - q.blockOffset
if index >= len(q.blockCache) || index < 0 {
//fmt.Printf("block cache overflown (N=%v O=%v, C=%v)", block.Number(), q.blockOffset, len(q.blockCache))
continue
}
// Skip any blocks that were not requested
hash := block.Hash()
if _, ok := request.Hashes[hash]; !ok {
errs = append(errs, fmt.Errorf("non-requested block %v", hash))
continue
}
// Otherwise merge the block and mark the hash block
q.blockCache[index] = block
delete(request.Hashes, hash)
delete(q.hashPool, hash)
q.blockPool[hash] = int(block.NumberU64())
}
// Return all failed fetches to the queue
for hash, index := range request.Hashes {
q.hashQueue.Push(hash, float32(index))
}
if len(errs) != 0 {
return fmt.Errorf("multiple failures: %v", errs)
}
return nil
}
// Alloc ensures that the block cache is the correct size, given a starting
// offset, and a memory cap.
func (q *queue) Alloc(offset int) {
q.lock.Lock()
defer q.lock.Unlock()
if q.blockOffset < offset {
q.blockOffset = offset
}
size := len(q.hashPool)
if size > blockCacheLimit {
size = blockCacheLimit
}
if len(q.blockCache) < size {
q.blockCache = append(q.blockCache, make([]*types.Block, size-len(q.blockCache))...)
}
}
