eth/downloader: implement concurrent header downloads

eth/downloader/peer.go

@@ -58,15 +58,18 @@ type peer struct {
 	id   string      // Unique identifier of the peer
 	head common.Hash // Hash of the peers latest known block
 
+	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
 
-	blockStarted   time.Time // Time instance when the last block (body)fetch was started
+	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
 
@@ -118,10 +121,12 @@ func (p *peer) Reset() {
 	p.lock.Lock()
 	defer p.lock.Unlock()
 
+	atomic.StoreInt32(&p.headerIdle, 0)
 	atomic.StoreInt32(&p.blockIdle, 0)
 	atomic.StoreInt32(&p.receiptIdle, 0)
 	atomic.StoreInt32(&p.stateIdle, 0)
 
+	p.headerThroughput = 0
 	p.blockThroughput = 0
 	p.receiptThroughput = 0
 	p.stateThroughput = 0
@@ -151,6 +156,24 @@ func (p *peer) Fetch61(request *fetchRequest) error {
 	return nil
 }
 
+// FetchHeaders sends a header retrieval request to the remote peer.
+func (p *peer) 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.getAbsHeaders(from, count, 0, false)
+
+	return nil
+}
+
 // FetchBodies sends a block body retrieval request to the remote peer.
 func (p *peer) FetchBodies(request *fetchRequest) error {
 	// Sanity check the protocol version
@@ -217,6 +240,13 @@ func (p *peer) FetchNodeData(request *fetchRequest) error {
 	return nil
 }
 
+// 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 *peer) SetHeadersIdle(delivered int) {
+	p.setIdle(p.headerStarted, delivered, &p.headerThroughput, &p.headerIdle)
+}
+
 // SetBlocksIdle sets the peer to idle, allowing it to execute new block retrieval
 // requests. Its estimated block retrieval throughput is updated with that measured
 // just now.
@@ -264,6 +294,15 @@ func (p *peer) setIdle(started time.Time, delivered int, throughput *float64, id
 	*throughput = (1-throughputImpact)*(*throughput) + throughputImpact*measured
 }
 
+// HeaderCapacity retrieves the peers header download allowance based on its
+// previously discovered throughput.
+func (p *peer) HeaderCapacity() int {
+	p.lock.RLock()
+	defer p.lock.RUnlock()
+
+	return int(math.Max(1, math.Min(p.headerThroughput*float64(headerTargetRTT)/float64(time.Second), float64(MaxHeaderFetch))))
+}
+
 // BlockCapacity retrieves the peers block download allowance based on its
 // previously discovered throughput.
 func (p *peer) BlockCapacity() int {
@@ -323,14 +362,15 @@ func (p *peer) String() string {
 	defer p.lock.RUnlock()
 
 	return fmt.Sprintf("Peer %s [%s]", p.id,
-		fmt.Sprintf("blocks %3.2f/s, ", p.blockThroughput)+
+		fmt.Sprintf("headers %3.2f/s, ", p.headerThroughput)+
+			fmt.Sprintf("blocks %3.2f/s, ", p.blockThroughput)+
 			fmt.Sprintf("receipts %3.2f/s, ", p.receiptThroughput)+
 			fmt.Sprintf("states %3.2f/s, ", p.stateThroughput)+
 			fmt.Sprintf("lacking %4d", len(p.lacking)),
 	)
 }
 
-// peerSet represents the collection of active peer participating in the block
+// peerSet represents the collection of active peer participating in the chain
 // download procedure.
 type peerSet struct {
 	peers map[string]*peer
@@ -359,7 +399,7 @@ func (ps *peerSet) Reset() {
 // 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 change of being used
+// average of all existing peers, to give it a realistic chance of being used
 // for data retrievals.
 func (ps *peerSet) Register(p *peer) error {
 	ps.lock.Lock()
@@ -369,15 +409,17 @@ func (ps *peerSet) Register(p *peer) error {
 		return errAlreadyRegistered
 	}
 	if len(ps.peers) > 0 {
-		p.blockThroughput, p.receiptThroughput, p.stateThroughput = 0, 0, 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))
@@ -441,6 +483,20 @@ func (ps *peerSet) BlockIdlePeers() ([]*peer, int) {
 	return ps.idlePeers(61, 61, idle, throughput)
 }
 
+// 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() ([]*peer, int) {
+	idle := func(p *peer) bool {
+		return atomic.LoadInt32(&p.headerIdle) == 0
+	}
+	throughput := func(p *peer) float64 {
+		p.lock.RLock()
+		defer p.lock.RUnlock()
+		return p.headerThroughput
+	}
+	return ps.idlePeers(62, 64, idle, throughput)
+}
+
 // BodyIdlePeers retrieves a flat list of all the currently body-idle peers within
 // the active peer set, ordered by their reputation.
 func (ps *peerSet) BodyIdlePeers() ([]*peer, int) {