// Contains the active peer-set of the downloader, maintaining both failures
// as well as reputation metrics to prioritize the block retrievals.
package downloader
import (
"errors"
"fmt"
"math"
"sync"
"sync/atomic"
"time"
"github.com/ethereum/go-ethereum/common"
"gopkg.in/fatih/set.v0"
)
type hashFetcherFn func(common.Hash) error
type blockFetcherFn func([]common.Hash) error
var (
errAlreadyFetching = errors.New("already fetching blocks from peer")
errAlreadyRegistered = errors.New("peer is already registered")
errNotRegistered = errors.New("peer is not registered")
)
// peer represents an active peer from which hashes and blocks are retrieved.
type peer struct {
id string // Unique identifier of the peer
head common.Hash // Hash of the peers latest known block
idle int32 // Current activity state of the peer (idle = 0, active = 1)
rep int32 // Simple peer reputation
capacity int32 // Number of blocks allowed to fetch per request
started time.Time // Time instance when the last fetch was started
ignored *set.Set // Set of hashes not to request (didn't have previously)
getHashes hashFetcherFn // Method to retrieve a batch of hashes (mockable for testing)
getBlocks blockFetcherFn // Method to retrieve a batch of blocks (mockable for testing)
version int // Eth protocol version number to switch strategies
}
// newPeer create a new downloader peer, with specific hash and block retrieval
// mechanisms.
func newPeer(id string, version int, head common.Hash, getHashes hashFetcherFn, getBlocks blockFetcherFn) *peer {
return &peer{
id: id,
head: head,
capacity: 1,
getHashes: getHashes,
getBlocks: getBlocks,
ignored: set.New(),
version: version,
}
}
// Reset clears the internal state of a peer entity.
func (p *peer) Reset() {
atomic.StoreInt32(&p.idle, 0)
atomic.StoreInt32(&p.capacity, 1)
p.ignored.Clear()
}
// Fetch sends a block retrieval request to the remote peer.
func (p *peer) Fetch(request *fetchRequest) error {
// Short circuit if the peer is already fetching
if !atomic.CompareAndSwapInt32(&p.idle, 0, 1) {
return errAlreadyFetching
}
p.started = time.Now()
// Convert the hash set to a retrievable slice
hashes := make([]common.Hash, 0, len(request.Hashes))
for hash, _ := range request.Hashes {
hashes = append(hashes, hash)
}
go p.getBlocks(hashes)
return nil
}
// SetIdle sets the peer to idle, allowing it to execute new retrieval requests.
// Its block retrieval allowance will also be updated either up- or downwards,
// depending on whether the previous fetch completed in time or not.
func (p *peer) SetIdle() {
// Update the peer's download allowance based on previous performance
scale := 2.0
if time.Since(p.started) > blockSoftTTL {
scale = 0.5
if time.Since(p.started) > blockHardTTL {
scale = 1 / float64(MaxBlockFetch) // reduces capacity to 1
}
}
for {
// Calculate the new download bandwidth allowance
prev := atomic.LoadInt32(&p.capacity)
next := int32(math.Max(1, math.Min(float64(MaxBlockFetch), float64(prev)*scale)))
// Try to update the old value
if atomic.CompareAndSwapInt32(&p.capacity, prev, next) {
// If we're having problems at 1 capacity, try to find better peers
if next == 1 {
p.Demote()
}
break
}
}
// Set the peer to idle to allow further block requests
atomic.StoreInt32(&p.idle, 0)
}
// Capacity retrieves the peers block download allowance based on its previously
// discovered bandwidth capacity.
func (p *peer) Capacity() int {
return int(atomic.LoadInt32(&p.capacity))
}
// Promote increases the peer's reputation.
func (p *peer) Promote() {
atomic.AddInt32(&p.rep, 1)
}
// Demote decreases the peer's reputation or leaves it at 0.
func (p *peer) Demote() {
for {
// Calculate the new reputation value
prev := atomic.LoadInt32(&p.rep)
next := prev / 2
// Try to update the old value
if atomic.CompareAndSwapInt32(&p.rep, prev, next) {
return
}
}
}
// String implements fmt.Stringer.
func (p *peer) String() string {
return fmt.Sprintf("Peer %s [%s]", p.id,
fmt.Sprintf("reputation %3d, ", atomic.LoadInt32(&p.rep))+
fmt.Sprintf("capacity %3d, ", atomic.LoadInt32(&p.capacity))+
fmt.Sprintf("ignored %4d", p.ignored.Size()),
)
}
// peerSet represents the collection of active peer participating in the block
// download procedure.
type peerSet struct {
peers map[string]*peer
lock sync.RWMutex
}
// newPeerSet creates a new peer set top track the active download sources.
func newPeerSet() *peerSet {
return &peerSet{
peers: make(map[string]*peer),
}
}
// Reset iterates over the current peer set, and resets each of the known peers
// to prepare for a next batch of block retrieval.
func (ps *peerSet) Reset() {
ps.lock.RLock()
defer ps.lock.RUnlock()
for _, peer := range ps.peers {
peer.Reset()
}
}
// Register injects a new peer into the working set, or returns an error if the
// peer is already known.
func (ps *peerSet) Register(p *peer) error {
ps.lock.Lock()
defer ps.lock.Unlock()
if _, ok := ps.peers[p.id]; ok {
return errAlreadyRegistered
}
ps.peers[p.id] = p
return nil
}
// Unregister removes a remote peer from the active set, disabling any further
// actions to/from that particular entity.
func (ps *peerSet) Unregister(id string) error {
ps.lock.Lock()
defer ps.lock.Unlock()
if _, ok := ps.peers[id]; !ok {
return errNotRegistered
}
delete(ps.peers, id)
return nil
}
// Peer retrieves the registered peer with the given id.
func (ps *peerSet) Peer(id string) *peer {
ps.lock.RLock()
defer ps.lock.RUnlock()
return ps.peers[id]
}
// Len returns if the current number of peers in the set.
func (ps *peerSet) Len() int {
ps.lock.RLock()
defer ps.lock.RUnlock()
return len(ps.peers)
}
// AllPeers retrieves a flat list of all the peers within the set.
func (ps *peerSet) AllPeers() []*peer {
ps.lock.RLock()
defer ps.lock.RUnlock()
list := make([]*peer, 0, len(ps.peers))
for _, p := range ps.peers {
list = append(list, p)
}
return list
}
// IdlePeers retrieves a flat list of all the currently idle peers within the
// active peer set, ordered by their reputation.
func (ps *peerSet) IdlePeers() []*peer {
ps.lock.RLock()
defer ps.lock.RUnlock()
list := make([]*peer, 0, len(ps.peers))
for _, p := range ps.peers {
if atomic.LoadInt32(&p.idle) == 0 {
list = append(list, p)
}
}
for i := 0; i < len(list); i++ {
for j := i + 1; j < len(list); j++ {
if atomic.LoadInt32(&list[i].rep) < atomic.LoadInt32(&list[j].rep) {
list[i], list[j] = list[j], list[i]
}
}
}
return list
}
