lnd.xprv/discovery/sync_manager.go
Olaoluwa Osuntokun 985902be27
Merge pull request #2916 from cfromknecht/split-syncer-query-reply
discovery: make gossip replies synchronous
2019-04-29 17:40:13 -07:00

652 lines
20 KiB
Go

package discovery
import (
"errors"
"sync"
"time"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/lightningnetwork/lnd/lnpeer"
"github.com/lightningnetwork/lnd/lnwire"
"github.com/lightningnetwork/lnd/routing/route"
"github.com/lightningnetwork/lnd/ticker"
)
const (
// DefaultSyncerRotationInterval is the default interval in which we'll
// rotate a single active syncer.
DefaultSyncerRotationInterval = 20 * time.Minute
// DefaultHistoricalSyncInterval is the default interval in which we'll
// force a historical sync to ensure we have as much of the public
// network as possible.
DefaultHistoricalSyncInterval = time.Hour
)
var (
// ErrSyncManagerExiting is an error returned when we attempt to
// start/stop a gossip syncer for a connected/disconnected peer, but the
// SyncManager has already been stopped.
ErrSyncManagerExiting = errors.New("sync manager exiting")
)
// newSyncer in an internal message we'll use within the SyncManager to signal
// that we should create a GossipSyncer for a newly connected peer.
type newSyncer struct {
// peer is the newly connected peer.
peer lnpeer.Peer
// doneChan serves as a signal to the caller that the SyncManager's
// internal state correctly reflects the stale active syncer.
doneChan chan struct{}
}
// staleSyncer is an internal message we'll use within the SyncManager to signal
// that a peer has disconnected and its GossipSyncer should be removed.
type staleSyncer struct {
// peer is the peer that has disconnected.
peer route.Vertex
// doneChan serves as a signal to the caller that the SyncManager's
// internal state correctly reflects the stale active syncer. This is
// needed to ensure we always create a new syncer for a flappy peer
// after they disconnect if they happened to be an active syncer.
doneChan chan struct{}
}
// SyncManagerCfg contains all of the dependencies required for the SyncManager
// to carry out its duties.
type SyncManagerCfg struct {
// ChainHash is a hash that indicates the specific network of the active
// chain.
ChainHash chainhash.Hash
// ChanSeries is an interface that provides access to a time series view
// of the current known channel graph. Each GossipSyncer enabled peer
// will utilize this in order to create and respond to channel graph
// time series queries.
ChanSeries ChannelGraphTimeSeries
// NumActiveSyncers is the number of peers for which we should have
// active syncers with. After reaching NumActiveSyncers, any future
// gossip syncers will be passive.
NumActiveSyncers int
// RotateTicker is a ticker responsible for notifying the SyncManager
// when it should rotate its active syncers. A single active syncer with
// a chansSynced state will be exchanged for a passive syncer in order
// to ensure we don't keep syncing with the same peers.
RotateTicker ticker.Ticker
// HistoricalSyncTicker is a ticker responsible for notifying the
// SyncManager when it should attempt a historical sync with a gossip
// sync peer.
HistoricalSyncTicker ticker.Ticker
}
// SyncManager is a subsystem of the gossiper that manages the gossip syncers
// for peers currently connected. When a new peer is connected, the manager will
// create its accompanying gossip syncer and determine whether it should have an
// ActiveSync or PassiveSync sync type based on how many other gossip syncers
// are currently active. Any ActiveSync gossip syncers are started in a
// round-robin manner to ensure we're not syncing with multiple peers at the
// same time. The first GossipSyncer registered with the SyncManager will
// attempt a historical sync to ensure we have as much of the public channel
// graph as possible.
type SyncManager struct {
start sync.Once
stop sync.Once
cfg SyncManagerCfg
// historicalSync allows us to perform an initial historical sync only
// _once_ with a peer during the SyncManager's startup.
historicalSync sync.Once
// newSyncers is a channel we'll use to process requests to create
// GossipSyncers for newly connected peers.
newSyncers chan *newSyncer
// staleSyncers is a channel we'll use to process requests to tear down
// GossipSyncers for disconnected peers.
staleSyncers chan *staleSyncer
// syncersMu guards the read and write access to the activeSyncers and
// inactiveSyncers maps below.
syncersMu sync.Mutex
// activeSyncers is the set of all syncers for which we are currently
// receiving graph updates from. The number of possible active syncers
// is bounded by NumActiveSyncers.
activeSyncers map[route.Vertex]*GossipSyncer
// inactiveSyncers is the set of all syncers for which we are not
// currently receiving new graph updates from.
inactiveSyncers map[route.Vertex]*GossipSyncer
wg sync.WaitGroup
quit chan struct{}
}
// newSyncManager constructs a new SyncManager backed by the given config.
func newSyncManager(cfg *SyncManagerCfg) *SyncManager {
return &SyncManager{
cfg: *cfg,
newSyncers: make(chan *newSyncer),
staleSyncers: make(chan *staleSyncer),
activeSyncers: make(
map[route.Vertex]*GossipSyncer, cfg.NumActiveSyncers,
),
inactiveSyncers: make(map[route.Vertex]*GossipSyncer),
quit: make(chan struct{}),
}
}
// Start starts the SyncManager in order to properly carry out its duties.
func (m *SyncManager) Start() {
m.start.Do(func() {
m.wg.Add(1)
go m.syncerHandler()
})
}
// Stop stops the SyncManager from performing its duties.
func (m *SyncManager) Stop() {
m.stop.Do(func() {
close(m.quit)
m.wg.Wait()
for _, syncer := range m.inactiveSyncers {
syncer.Stop()
}
for _, syncer := range m.activeSyncers {
syncer.Stop()
}
})
}
// syncerHandler is the SyncManager's main event loop responsible for:
//
// 1. Creating and tearing down GossipSyncers for connected/disconnected peers.
// 2. Finding new peers to receive graph updates from to ensure we don't only
// receive them from the same set of peers.
// 3. Finding new peers to force a historical sync with to ensure we have as
// much of the public network as possible.
//
// NOTE: This must be run as a goroutine.
func (m *SyncManager) syncerHandler() {
defer m.wg.Done()
m.cfg.RotateTicker.Resume()
defer m.cfg.RotateTicker.Stop()
m.cfg.HistoricalSyncTicker.Resume()
defer m.cfg.HistoricalSyncTicker.Stop()
var (
// attemptInitialHistoricalSync determines whether we should
// attempt an initial historical sync when a new peer connects.
attemptInitialHistoricalSync = true
// initialHistoricalSyncCompleted serves as a barrier when
// initializing new active GossipSyncers. If false, the initial
// historical sync has not completed, so we'll defer
// initializing any active GossipSyncers. If true, then we can
// transition the GossipSyncer immediately. We set up this
// barrier to ensure we have most of the graph before attempting
// to accept new updates at tip.
initialHistoricalSyncCompleted = false
// initialHistoricalSyncer is the syncer we are currently
// performing an initial historical sync with.
initialHistoricalSyncer *GossipSyncer
// initialHistoricalSyncSignal is a signal that will fire once
// the intiial historical sync has been completed. This is
// crucial to ensure that another historical sync isn't
// attempted just because the initialHistoricalSyncer was
// disconnected.
initialHistoricalSyncSignal chan struct{}
)
for {
select {
// A new peer has been connected, so we'll create its
// accompanying GossipSyncer.
case newSyncer := <-m.newSyncers:
// If we already have a syncer, then we'll exit early as
// we don't want to override it.
if _, ok := m.GossipSyncer(newSyncer.peer.PubKey()); ok {
close(newSyncer.doneChan)
continue
}
s := m.createGossipSyncer(newSyncer.peer)
m.syncersMu.Lock()
switch {
// If we've exceeded our total number of active syncers,
// we'll initialize this GossipSyncer as passive.
case len(m.activeSyncers) >= m.cfg.NumActiveSyncers:
fallthrough
// Otherwise, it should be initialized as active. If the
// initial historical sync has yet to complete, then
// we'll declare is as passive and attempt to transition
// it when the initial historical sync completes.
case !initialHistoricalSyncCompleted:
s.setSyncType(PassiveSync)
m.inactiveSyncers[s.cfg.peerPub] = s
// The initial historical sync has completed, so we can
// immediately start the GossipSyncer as active.
default:
s.setSyncType(ActiveSync)
m.activeSyncers[s.cfg.peerPub] = s
}
m.syncersMu.Unlock()
s.Start()
// Once we create the GossipSyncer, we'll signal to the
// caller that they can proceed since the SyncManager's
// internal state has been updated.
close(newSyncer.doneChan)
// We'll force a historical sync with the first peer we
// connect to, to ensure we get as much of the graph as
// possible.
if !attemptInitialHistoricalSync {
continue
}
log.Debugf("Attempting initial historical sync with "+
"GossipSyncer(%x)", s.cfg.peerPub)
if err := s.historicalSync(); err != nil {
log.Errorf("Unable to attempt initial "+
"historical sync with "+
"GossipSyncer(%x): %v", s.cfg.peerPub,
err)
continue
}
// Once the historical sync has started, we'll get a
// keep track of the corresponding syncer to properly
// handle disconnects. We'll also use a signal to know
// when the historical sync completed.
attemptInitialHistoricalSync = false
initialHistoricalSyncer = s
initialHistoricalSyncSignal = s.ResetSyncedSignal()
// An existing peer has disconnected, so we'll tear down its
// corresponding GossipSyncer.
case staleSyncer := <-m.staleSyncers:
// Once the corresponding GossipSyncer has been stopped
// and removed, we'll signal to the caller that they can
// proceed since the SyncManager's internal state has
// been updated.
m.removeGossipSyncer(staleSyncer.peer)
close(staleSyncer.doneChan)
// If we don't have an initialHistoricalSyncer, or we do
// but it is not the peer being disconnected, then we
// have nothing left to do and can proceed.
switch {
case initialHistoricalSyncer == nil:
fallthrough
case staleSyncer.peer != initialHistoricalSyncer.cfg.peerPub:
continue
}
// Otherwise, our initialHistoricalSyncer corresponds to
// the peer being disconnected, so we'll have to find a
// replacement.
log.Debug("Finding replacement for intitial " +
"historical sync")
s := m.forceHistoricalSync()
if s == nil {
log.Debug("No eligible replacement found " +
"for initial historical sync")
attemptInitialHistoricalSync = true
continue
}
log.Debugf("Replaced initial historical "+
"GossipSyncer(%v) with GossipSyncer(%x)",
staleSyncer.peer, s.cfg.peerPub)
initialHistoricalSyncer = s
initialHistoricalSyncSignal = s.ResetSyncedSignal()
// Our initial historical sync signal has completed, so we'll
// nil all of the relevant fields as they're no longer needed.
case <-initialHistoricalSyncSignal:
initialHistoricalSyncer = nil
initialHistoricalSyncSignal = nil
initialHistoricalSyncCompleted = true
log.Debug("Initial historical sync completed")
// With the initial historical sync complete, we can
// begin receiving new graph updates at tip. We'll
// determine whether we can have any more active
// GossipSyncers. If we do, we'll randomly select some
// that are currently passive to transition.
m.syncersMu.Lock()
numActiveLeft := m.cfg.NumActiveSyncers - len(m.activeSyncers)
if numActiveLeft <= 0 {
m.syncersMu.Unlock()
continue
}
log.Debugf("Attempting to transition %v passive "+
"GossipSyncers to active", numActiveLeft)
for i := 0; i < numActiveLeft; i++ {
chooseRandomSyncer(
m.inactiveSyncers, m.transitionPassiveSyncer,
)
}
m.syncersMu.Unlock()
// Our RotateTicker has ticked, so we'll attempt to rotate a
// single active syncer with a passive one.
case <-m.cfg.RotateTicker.Ticks():
m.rotateActiveSyncerCandidate()
// Our HistoricalSyncTicker has ticked, so we'll randomly select
// a peer and force a historical sync with them.
case <-m.cfg.HistoricalSyncTicker.Ticks():
m.forceHistoricalSync()
case <-m.quit:
return
}
}
}
// createGossipSyncer creates the GossipSyncer for a newly connected peer.
func (m *SyncManager) createGossipSyncer(peer lnpeer.Peer) *GossipSyncer {
nodeID := route.Vertex(peer.PubKey())
log.Infof("Creating new GossipSyncer for peer=%x", nodeID[:])
encoding := lnwire.EncodingSortedPlain
s := newGossipSyncer(gossipSyncerCfg{
chainHash: m.cfg.ChainHash,
peerPub: nodeID,
channelSeries: m.cfg.ChanSeries,
encodingType: encoding,
chunkSize: encodingTypeToChunkSize[encoding],
batchSize: requestBatchSize,
sendToPeer: func(msgs ...lnwire.Message) error {
return peer.SendMessageLazy(false, msgs...)
},
sendToPeerSync: func(msgs ...lnwire.Message) error {
return peer.SendMessageLazy(true, msgs...)
},
})
// Gossip syncers are initialized by default in a PassiveSync type
// and chansSynced state so that they can reply to any peer queries or
// handle any sync transitions.
s.setSyncState(chansSynced)
s.setSyncType(PassiveSync)
return s
}
// removeGossipSyncer removes all internal references to the disconnected peer's
// GossipSyncer and stops it. In the event of an active GossipSyncer being
// disconnected, a passive GossipSyncer, if any, will take its place.
func (m *SyncManager) removeGossipSyncer(peer route.Vertex) {
m.syncersMu.Lock()
defer m.syncersMu.Unlock()
s, ok := m.gossipSyncer(peer)
if !ok {
return
}
log.Infof("Removing GossipSyncer for peer=%v", peer)
// We'll stop the GossipSyncer for the disconnected peer in a goroutine
// to prevent blocking the SyncManager.
go s.Stop()
// If it's a non-active syncer, then we can just exit now.
if _, ok := m.inactiveSyncers[peer]; ok {
delete(m.inactiveSyncers, peer)
return
}
// Otherwise, we'll need find a new one to replace it, if any.
delete(m.activeSyncers, peer)
newActiveSyncer := chooseRandomSyncer(
m.inactiveSyncers, m.transitionPassiveSyncer,
)
if newActiveSyncer == nil {
return
}
log.Debugf("Replaced active GossipSyncer(%x) with GossipSyncer(%x)",
peer, newActiveSyncer.cfg.peerPub)
}
// rotateActiveSyncerCandidate rotates a single active syncer. In order to
// achieve this, the active syncer must be in a chansSynced state in order to
// process the sync transition.
func (m *SyncManager) rotateActiveSyncerCandidate() {
m.syncersMu.Lock()
defer m.syncersMu.Unlock()
// If we couldn't find an eligible active syncer to rotate, we can
// return early.
activeSyncer := chooseRandomSyncer(m.activeSyncers, nil)
if activeSyncer == nil {
log.Debug("No eligible active syncer to rotate")
return
}
// Similarly, if we don't have a candidate to rotate with, we can return
// early as well.
candidate := chooseRandomSyncer(m.inactiveSyncers, nil)
if candidate == nil {
log.Debug("No eligible candidate to rotate active syncer")
return
}
// Otherwise, we'll attempt to transition each syncer to their
// respective new sync type.
log.Debugf("Rotating active GossipSyncer(%x) with GossipSyncer(%x)",
activeSyncer.cfg.peerPub, candidate.cfg.peerPub)
if err := m.transitionActiveSyncer(activeSyncer); err != nil {
log.Errorf("Unable to transition active GossipSyncer(%x): %v",
activeSyncer.cfg.peerPub, err)
return
}
if err := m.transitionPassiveSyncer(candidate); err != nil {
log.Errorf("Unable to transition passive GossipSyncer(%x): %v",
activeSyncer.cfg.peerPub, err)
return
}
}
// transitionActiveSyncer transitions an active syncer to a passive one.
//
// NOTE: This must be called with the syncersMu lock held.
func (m *SyncManager) transitionActiveSyncer(s *GossipSyncer) error {
log.Debugf("Transitioning active GossipSyncer(%x) to passive",
s.cfg.peerPub)
if err := s.ProcessSyncTransition(PassiveSync); err != nil {
return err
}
delete(m.activeSyncers, s.cfg.peerPub)
m.inactiveSyncers[s.cfg.peerPub] = s
return nil
}
// transitionPassiveSyncer transitions a passive syncer to an active one.
//
// NOTE: This must be called with the syncersMu lock held.
func (m *SyncManager) transitionPassiveSyncer(s *GossipSyncer) error {
log.Debugf("Transitioning passive GossipSyncer(%x) to active",
s.cfg.peerPub)
if err := s.ProcessSyncTransition(ActiveSync); err != nil {
return err
}
delete(m.inactiveSyncers, s.cfg.peerPub)
m.activeSyncers[s.cfg.peerPub] = s
return nil
}
// forceHistoricalSync chooses a syncer with a remote peer at random and forces
// a historical sync with it.
func (m *SyncManager) forceHistoricalSync() *GossipSyncer {
m.syncersMu.Lock()
defer m.syncersMu.Unlock()
// We'll sample from both sets of active and inactive syncers in the
// event that we don't have any inactive syncers.
return chooseRandomSyncer(m.gossipSyncers(), func(s *GossipSyncer) error {
return s.historicalSync()
})
}
// chooseRandomSyncer iterates through the set of syncers given and returns the
// first one which was able to successfully perform the action enclosed in the
// function closure.
//
// NOTE: It's possible for a nil value to be returned if there are no eligible
// candidate syncers.
func chooseRandomSyncer(syncers map[route.Vertex]*GossipSyncer,
action func(*GossipSyncer) error) *GossipSyncer {
for _, s := range syncers {
// Only syncers in a chansSynced state are viable for sync
// transitions, so skip any that aren't.
if s.syncState() != chansSynced {
continue
}
if action != nil {
if err := action(s); err != nil {
log.Debugf("Skipping eligible candidate "+
"GossipSyncer(%x): %v", s.cfg.peerPub,
err)
continue
}
}
return s
}
return nil
}
// InitSyncState is called by outside sub-systems when a connection is
// established to a new peer that understands how to perform channel range
// queries. We'll allocate a new GossipSyncer for it, and start any goroutines
// needed to handle new queries. The first GossipSyncer registered with the
// SyncManager will attempt a historical sync to ensure we have as much of the
// public channel graph as possible.
//
// TODO(wilmer): Only mark as ActiveSync if this isn't a channel peer.
func (m *SyncManager) InitSyncState(peer lnpeer.Peer) error {
done := make(chan struct{})
select {
case m.newSyncers <- &newSyncer{
peer: peer,
doneChan: done,
}:
case <-m.quit:
return ErrSyncManagerExiting
}
select {
case <-done:
return nil
case <-m.quit:
return ErrSyncManagerExiting
}
}
// PruneSyncState is called by outside sub-systems once a peer that we were
// previously connected to has been disconnected. In this case we can stop the
// existing GossipSyncer assigned to the peer and free up resources.
func (m *SyncManager) PruneSyncState(peer route.Vertex) {
done := make(chan struct{})
// We avoid returning an error when the SyncManager is stopped since the
// GossipSyncer will be stopped then anyway.
select {
case m.staleSyncers <- &staleSyncer{
peer: peer,
doneChan: done,
}:
case <-m.quit:
return
}
select {
case <-done:
case <-m.quit:
}
}
// GossipSyncer returns the associated gossip syncer of a peer. The boolean
// returned signals whether there exists a gossip syncer for the peer.
func (m *SyncManager) GossipSyncer(peer route.Vertex) (*GossipSyncer, bool) {
m.syncersMu.Lock()
defer m.syncersMu.Unlock()
return m.gossipSyncer(peer)
}
// gossipSyncer returns the associated gossip syncer of a peer. The boolean
// returned signals whether there exists a gossip syncer for the peer.
func (m *SyncManager) gossipSyncer(peer route.Vertex) (*GossipSyncer, bool) {
syncer, ok := m.inactiveSyncers[peer]
if ok {
return syncer, true
}
syncer, ok = m.activeSyncers[peer]
if ok {
return syncer, true
}
return nil, false
}
// GossipSyncers returns all of the currently initialized gossip syncers.
func (m *SyncManager) GossipSyncers() map[route.Vertex]*GossipSyncer {
m.syncersMu.Lock()
defer m.syncersMu.Unlock()
return m.gossipSyncers()
}
// gossipSyncers returns all of the currently initialized gossip syncers.
func (m *SyncManager) gossipSyncers() map[route.Vertex]*GossipSyncer {
numSyncers := len(m.inactiveSyncers) + len(m.activeSyncers)
syncers := make(map[route.Vertex]*GossipSyncer, numSyncers)
for _, syncer := range m.inactiveSyncers {
syncers[syncer.cfg.peerPub] = syncer
}
for _, syncer := range m.activeSyncers {
syncers[syncer.cfg.peerPub] = syncer
}
return syncers
}