The peer module contains the peer node used by the downloader to encapsulate the throughput, whether it is idle, and record the information that failed before.
// peerConnection represents an active peer from which hashes and blocks are retrieved.
type peerConnection struct {
id string // Unique identifier of the peer
headerIdle int32 // Current header activity state of the peer (idle = 0, active = 1)
blockIdle int32 // Current block activity state of the peer (idle = 0, active = 1)
receiptIdle int32 // Current receipt activity state of the peer (idle = 0, active = 1)
stateIdle int32 // Current node data activity state of the peer (idle = 0, active = 1)
headerThroughput float64 // Number of headers measured to be retrievable per second
blockThroughput float64 // Number of blocks (bodies) measured to be retrievable per second
receiptThroughput float64 // Number of receipts measured to be retrievable per second
stateThroughput float64 // Number of node data pieces measured to be retrievable per second
rtt time.Duration // Request round trip time to track responsiveness (QoS)
headerStarted time.Time // Time instance when the last header fetch was started
blockStarted time.Time // Time instance when the last block (body) fetch was started
receiptStarted time.Time // Time instance when the last receipt fetch was started
stateStarted time.Time // Time instance when the last node data fetch was started
lacking map[common.Hash]struct{} // Set of hashes not to request (didn't have previously)
peer Peer // remote peer
version int // Eth protocol version number to switch strategies
log log.Logger // Contextual logger to add extra infos to peer logs
lock sync.RWMutex
}FetchHeaders Functions such as FetchHeaders FetchBodies mainly call the function of eth.peer to send data requests.
// FetchHeaders sends a header retrieval request to the remote peer.
func (p *peerConnection) FetchHeaders(from uint64, count int) error {
// Sanity check the protocol version
if p.version < 62 {
panic(fmt.Sprintf("header fetch [eth/62+] requested on eth/%d", p.version))
}
// Short circuit if the peer is already fetching
if !atomic.CompareAndSwapInt32(&p.headerIdle, 0, 1) {
return errAlreadyFetching
}
p.headerStarted = time.Now()
// Issue the header retrieval request (absolut upwards without gaps)
go p.peer.RequestHeadersByNumber(from, count, 0, false)
return nil
}SetHeadersIdle function SetHeadersIdle, SetBlocksIdle and other functions Set the peer's state to idle, allowing it to execute new requests. At the same time, the throughput of the link is re-evaluated by the amount of data transmitted this time.
// SetHeadersIdle sets the peer to idle, allowing it to execute new header retrieval
// requests. Its estimated header retrieval throughput is updated with that measured
// just now.
func (p *peerConnection) SetHeadersIdle(delivered int) {
p.setIdle(p.headerStarted, delivered, &p.headerThroughput, &p.headerIdle)
}setIdle
// setIdle sets the peer to idle, allowing it to execute new retrieval requests.
// Its estimated retrieval throughput is updated with that measured just now.
func (p *peerConnection) setIdle(started time.Time, delivered int, throughput *float64, idle *int32) {
// Irrelevant of the scaling, make sure the peer ends up idle
// in thread-safe env, must use atomic to set value, or use mutex as well
defer atomic.StoreInt32(idle, 0)
p.lock.Lock()
defer p.lock.Unlock()
// If nothing was delivered (hard timeout / unavailable data), reduce throughput to minimum
if delivered == 0 {
*throughput = 0
return
}
// Otherwise update the throughput with a new measurement
elapsed := time.Since(started) + 1 // +1 (ns) to ensure non-zero divisor
measured := float64(delivered) / (float64(elapsed) / float64(time.Second))
// measurementImpact = 0.1 , new_throughput = old_throughput *0.9 + current_throughput *0.1
*throughput = (1-measurementImpact)*(*throughput) + measurementImpact*measured
// RTT
p.rtt = time.Duration((1-measurementImpact)*float64(p.rtt) + measurementImpact*float64(elapsed))
p.log.Trace("Peer throughput measurements updated",
"hps", p.headerThroughput, "bps", p.blockThroughput,
"rps", p.receiptThroughput, "sps", p.stateThroughput,
"miss", len(p.lacking), "rtt", p.rtt)
}The HeadersCapacity function is used to return the throughput allowed by the current link.
// HeaderCapacity retrieves the peers header download allowance based on its
// previously discovered throughput.
func (p *peerConnection) HeaderCapacity(targetRTT time.Duration) int {
p.lock.RLock()
defer p.lock.RUnlock()
// This is a bit strange. The larger the targetRTT, the more requests you have.
return int(math.Min(1+math.Max(1, p.headerThroughput*float64(targetRTT)/float64(time.Second)), float64(MaxHeaderFetch)))
}Lacks is used to mark the last failure, so that the next request will not pass this peer.
// MarkLacking appends a new entity to the set of items (blocks, receipts, states)
// that a peer is known not to have (i.e. have been requested before). If the
// set reaches its maximum allowed capacity, items are randomly dropped off.
func (p *peerConnection) MarkLacking(hash common.Hash) {
p.lock.Lock()
defer p.lock.Unlock()
for len(p.lacking) >= maxLackingHashes {
for drop := range p.lacking {
delete(p.lacking, drop)
break
}
}
p.lacking[hash] = struct{}{}
}
// Lacks retrieves whether the hash of a blockchain item is on the peers lacking
// list (i.e. whether we know that the peer does not have it).
func (p *peerConnection) Lacks(hash common.Hash) bool {
p.lock.RLock()
defer p.lock.RUnlock()
_, ok := p.lacking[hash]
return ok
}// peerSet represents the collection of active peer participating in the chain
// download procedure.
type peerSet struct {
peers map[string]*peerConnection
newPeerFeed event.Feed
peerDropFeed event.Feed
lock sync.RWMutex
}Register and UnRegister
// Register injects a new peer into the working set, or returns an error if the
// peer is already known.
//
// The method also sets the starting throughput values of the new peer to the
// average of all existing peers, to give it a realistic chance of being used
// for data retrievals.
func (ps *peerSet) Register(p *peerConnection) error {
// Retrieve the current median RTT as a sane default
p.rtt = ps.medianRTT()
// Register the new peer with some meaningful defaults
ps.lock.Lock()
if _, ok := ps.peers[p.id]; ok {
ps.lock.Unlock()
return errAlreadyRegistered
}
if len(ps.peers) > 0 {
p.headerThroughput, p.blockThroughput, p.receiptThroughput, p.stateThroughput = 0, 0, 0, 0
for _, peer := range ps.peers {
peer.lock.RLock()
p.headerThroughput += peer.headerThroughput
p.blockThroughput += peer.blockThroughput
p.receiptThroughput += peer.receiptThroughput
p.stateThroughput += peer.stateThroughput
peer.lock.RUnlock()
}
p.headerThroughput /= float64(len(ps.peers))
p.blockThroughput /= float64(len(ps.peers))
p.receiptThroughput /= float64(len(ps.peers))
p.stateThroughput /= float64(len(ps.peers))
}
ps.peers[p.id] = p
ps.lock.Unlock()
ps.newPeerFeed.Send(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()
p, ok := ps.peers[id]
if !ok {
defer ps.lock.Unlock()
return errNotRegistered
}
delete(ps.peers, id)
ps.lock.Unlock()
ps.peerDropFeed.Send(p)
return nil
}HeaderIdlePeers
// HeaderIdlePeers retrieves a flat list of all the currently header-idle peers
// within the active peer set, ordered by their reputation.
func (ps *peerSet) HeaderIdlePeers() ([]*peerConnection, int) {
idle := func(p *peerConnection) bool {
return atomic.LoadInt32(&p.headerIdle) == 0
}
throughput := func(p *peerConnection) float64 {
p.lock.RLock()
defer p.lock.RUnlock()
return p.headerThroughput
}
return ps.idlePeers(62, 64, idle, throughput)
}
// idlePeers retrieves a flat list of all currently idle peers satisfying the
// protocol version constraints, using the provided function to check idleness.
// The resulting set of peers are sorted by their measure throughput.
func (ps *peerSet) idlePeers(minProtocol, maxProtocol int, idleCheck func(*peerConnection) bool, throughput func(*peerConnection) float64) ([]*peerConnection, int) {
ps.lock.RLock()
defer ps.lock.RUnlock()
idle, total := make([]*peerConnection, 0, len(ps.peers)), 0
for _, p := range ps.peers {
if p.version >= minProtocol && p.version <= maxProtocol {
if idleCheck(p) {
idle = append(idle, p)
}
total++
}
}
for i := 0; i < len(idle); i++ { // Bubble sorting, from high throughput to low throughput.
for j := i + 1; j < len(idle); j++ {
if throughput(idle[i]) < throughput(idle[j]) {
idle[i], idle[j] = idle[j], idle[i]
}
}
}
return idle, total
}medianRTT, find the median of the RTT of the peerset,
// medianRTT returns the median RTT of te peerset, considering only the tuning
// peers if there are more peers available.
// qos: quality of service
func(ps * peerSet) medianRTT() time.Duration {
// Gather all the currnetly measured round trip times
ps.lock.RLock()
defer ps.lock.RUnlock()
rtts: = make([] float64, 0, len(ps.peers))
for _, p: = range ps.peers {
p.lock.RLock()
rtts = append(rtts, float64(p.rtt))
p.lock.RUnlock()
}
sort.Float64s(rtts)
median: = rttMaxEstimate
if qosTuningPeers <= len(rtts) {
median = time.Duration(rtts[qosTuningPeers / 2]) // Median of our tuning peers
} else if len(rtts) > 0 {
median = time.Duration(rtts[len(rtts) / 2]) // Median of our connected peers (maintain even like this some baseline qos)
}
// Restrict the RTT into some QoS defaults, irrelevant of true RTT
if median < rttMinEstimate {
median = rttMinEstimate
}
if median > rttMaxEstimate {
median = rttMaxEstimate
}
return median
}