statesync 用来获取pivot point所指定的区块的所有的state 的trie树，也就是所有的账号的信息，包括普通账号和合约账户。
stateSync调度下载由给定state root所定义的特定state trie的请求。
// stateSync schedules requests for downloading a particular state trie defined
// by a given state root.
type stateSync struct {
d *Downloader // Downloader instance to access and manage current peerset
sched *trie.TrieSync // State trie sync scheduler defining the tasks
keccak hash.Hash // Keccak256 hasher to verify deliveries with
tasks map[common.Hash]*stateTask // Set of tasks currently queued for retrieval
numUncommitted int
bytesUncommitted int
deliver chan *stateReq // Delivery channel multiplexing peer responses
cancel chan struct{} // Channel to signal a termination request
cancelOnce sync.Once // Ensures cancel only ever gets called once
done chan struct{} // Channel to signal termination completion
err error // Any error hit during sync (set before completion)
}
构造函数
func newStateSync(d *Downloader, root common.Hash) *stateSync {
return &stateSync{
d: d,
sched: state.NewStateSync(root, d.stateDB),
keccak: sha3.NewKeccak256(),
tasks: make(map[common.Hash]*stateTask),
deliver: make(chan *stateReq),
cancel: make(chan struct{}),
done: make(chan struct{}),
}
}
NewStateSync
// NewStateSync create a new state trie download scheduler.
func NewStateSync(root common.Hash, database trie.DatabaseReader) *trie.TrieSync {
var syncer *trie.TrieSync
callback := func(leaf []byte, parent common.Hash) error {
var obj Account
if err := rlp.Decode(bytes.NewReader(leaf), &obj); err != nil {
return err
}
syncer.AddSubTrie(obj.Root, 64, parent, nil)
syncer.AddRawEntry(common.BytesToHash(obj.CodeHash), 64, parent)
return nil
}
syncer = trie.NewTrieSync(root, database, callback)
return syncer
}
syncState， 这个函数是downloader调用的。
// syncState starts downloading state with the given root hash.
func (d *Downloader) syncState(root common.Hash) *stateSync {
s := newStateSync(d, root)
select {
case d.stateSyncStart <- s:
case <-d.quitCh:
s.err = errCancelStateFetch
close(s.done)
}
return s
}
在downloader中启动了一个新的goroutine 来运行stateFetcher函数。 这个函数首先试图往stateSyncStart通道来以获取信息。 而syncState这个函数会给stateSyncStart通道发送数据。
// stateFetcher manages the active state sync and accepts requests
// on its behalf.
func (d *Downloader) stateFetcher() {
for {
select {
case s := <-d.stateSyncStart:
for next := s; next != nil; { // 这个for循环代表了downloader可以通过发送信号来随时改变需要同步的对象。
next = d.runStateSync(next)
}
case <-d.stateCh:
// Ignore state responses while no sync is running.
case <-d.quitCh:
return
}
}
}
我们下面看看哪里会调用syncState()函数。processFastSyncContent这个函数会在最开始发现peer的时候启动。
// processFastSyncContent takes fetch results from the queue and writes them to the
// database. It also controls the synchronisation of state nodes of the pivot block.
func (d *Downloader) processFastSyncContent(latest *types.Header) error {
// Start syncing state of the reported head block.
// This should get us most of the state of the pivot block.
stateSync := d.syncState(latest.Root)
runStateSync,这个方法从stateCh获取已经下载好的状态，然后把他投递到deliver通道上等待别人处理。
// runStateSync runs a state synchronisation until it completes or another root
// hash is requested to be switched over to.
func (d *Downloader) runStateSync(s *stateSync) *stateSync {
var (
active = make(map[string]*stateReq) // Currently in-flight requests
finished []*stateReq // Completed or failed requests
timeout = make(chan *stateReq) // Timed out active requests
)
defer func() {
// Cancel active request timers on exit. Also set peers to idle so they're
// available for the next sync.
for _, req := range active {
req.timer.Stop()
req.peer.SetNodeDataIdle(len(req.items))
}
}()
// Run the state sync.
// 运行状态同步
go s.run()
defer s.Cancel()
// Listen for peer departure events to cancel assigned tasks
peerDrop := make(chan *peerConnection, 1024)
peerSub := s.d.peers.SubscribePeerDrops(peerDrop)
defer peerSub.Unsubscribe()
for {
// Enable sending of the first buffered element if there is one.
var (
deliverReq *stateReq
deliverReqCh chan *stateReq
)
if len(finished) > 0 {
deliverReq = finished[0]
deliverReqCh = s.deliver
}
select {
// The stateSync lifecycle:
// 另外一个stateSync申请运行。 我们退出。
case next := <-d.stateSyncStart:
return next
case <-s.done:
return nil
// Send the next finished request to the current sync:
// 发送已经下载好的数据给sync
case deliverReqCh <- deliverReq:
finished = append(finished[:0], finished[1:]...)
// Handle incoming state packs:
// 处理进入的数据包。 downloader接收到state的数据会发送到这个通道上面。
case pack := <-d.stateCh:
// Discard any data not requested (or previsouly timed out)
req := active[pack.PeerId()]
if req == nil {
log.Debug("Unrequested node data", "peer", pack.PeerId(), "len", pack.Items())
continue
}
// Finalize the request and queue up for processing
req.timer.Stop()
req.response = pack.(*statePack).states
finished = append(finished, req)
delete(active, pack.PeerId())
// Handle dropped peer connections:
case p := <-peerDrop:
// Skip if no request is currently pending
req := active[p.id]
if req == nil {
continue
}
// Finalize the request and queue up for processing
req.timer.Stop()
req.dropped = true
finished = append(finished, req)
delete(active, p.id)
// Handle timed-out requests:
case req := <-timeout:
// If the peer is already requesting something else, ignore the stale timeout.
// This can happen when the timeout and the delivery happens simultaneously,
// causing both pathways to trigger.
if active[req.peer.id] != req {
continue
}
// Move the timed out data back into the download queue
finished = append(finished, req)
delete(active, req.peer.id)
// Track outgoing state requests:
case req := <-d.trackStateReq:
// If an active request already exists for this peer, we have a problem. In
// theory the trie node schedule must never assign two requests to the same
// peer. In practive however, a peer might receive a request, disconnect and
// immediately reconnect before the previous times out. In this case the first
// request is never honored, alas we must not silently overwrite it, as that
// causes valid requests to go missing and sync to get stuck.
if old := active[req.peer.id]; old != nil {
log.Warn("Busy peer assigned new state fetch", "peer", old.peer.id)
// Make sure the previous one doesn't get siletly lost
old.timer.Stop()
old.dropped = true
finished = append(finished, old)
}
// Start a timer to notify the sync loop if the peer stalled.
req.timer = time.AfterFunc(req.timeout, func() {
select {
case timeout <- req:
case <-s.done:
// Prevent leaking of timer goroutines in the unlikely case where a
// timer is fired just before exiting runStateSync.
}
})
active[req.peer.id] = req
}
}
}
run和loop方法，获取任务，分配任务，获取结果。
func (s *stateSync) run() {
s.err = s.loop()
close(s.done)
}
// loop is the main event loop of a state trie sync. It it responsible for the
// assignment of new tasks to peers (including sending it to them) as well as
// for the processing of inbound data. Note, that the loop does not directly
// receive data from peers, rather those are buffered up in the downloader and
// pushed here async. The reason is to decouple processing from data receipt
// and timeouts.
func (s *stateSync) loop() error {
// Listen for new peer events to assign tasks to them
newPeer := make(chan *peerConnection, 1024)
peerSub := s.d.peers.SubscribeNewPeers(newPeer)
defer peerSub.Unsubscribe()
// Keep assigning new tasks until the sync completes or aborts
// 一直等到 sync完成或者被被终止
for s.sched.Pending() > 0 {
// 把数据从缓存里面刷新到持久化存储里面。 这也就是命令行 --cache指定的大小。
if err := s.commit(false); err != nil {
return err
}
// 指派任务，
s.assignTasks()
// Tasks assigned, wait for something to happen
select {
case <-newPeer:
// New peer arrived, try to assign it download tasks
case <-s.cancel:
return errCancelStateFetch
case req := <-s.deliver:
// 接收到runStateSync方法投递过来的返回信息，注意 返回信息里面包含了成功请求的也包含了未成功请求的。
// Response, disconnect or timeout triggered, drop the peer if stalling
log.Trace("Received node data response", "peer", req.peer.id, "count", len(req.response), "dropped", req.dropped, "timeout", !req.dropped && req.timedOut())
if len(req.items) <= 2 && !req.dropped && req.timedOut() {
// 2 items are the minimum requested, if even that times out, we've no use of
// this peer at the moment.
log.Warn("Stalling state sync, dropping peer", "peer", req.peer.id)
s.d.dropPeer(req.peer.id)
}
// Process all the received blobs and check for stale delivery
stale, err := s.process(req)
if err != nil {
log.Warn("Node data write error", "err", err)
return err
}
// The the delivery contains requested data, mark the node idle (otherwise it's a timed out delivery)
if !stale {
req.peer.SetNodeDataIdle(len(req.response))
}
}
}
return s.commit(true)
}