eth, eth/downloader: make synchronize thread safe

eth/downloader/downloader.go

@@ -68,8 +68,7 @@ type Downloader struct {
 	getBlock getBlockFn
 
 	// Status
-	fetchingHashes    int32
-	downloadingBlocks int32
+	synchronizing int32
 
 	// Channels
 	newPeerCh chan *peer
@@ -120,43 +119,26 @@ func (d *Downloader) UnregisterPeer(id string) {
 	delete(d.peers, id)
 }
 
-// SynchroniseWithPeer will select the peer and use it for synchronizing. If an empty string is given
+// Synchronize will select the peer and use it for synchronizing. If an empty string is given
 // it will use the best peer possible and synchronize if it's TD is higher than our own. If any of the
 // checks fail an error will be returned. This method is synchronous
-func (d *Downloader) Synchronise(id string, hash common.Hash) error {
-	// Make sure it's doing neither. Once done we can restart the
-	// downloading process if the TD is higher. For now just get on
-	// with whatever is going on. This prevents unnecessary switching.
-	if d.isBusy() {
-		return errBusy
+func (d *Downloader) Synchronize(id string, hash common.Hash) error {
+	// Make sure only one goroutine is ever allowed past this point at once
+	if !atomic.CompareAndSwapInt32(&d.synchronizing, 0, 1) {
+		return nil
 	}
+	defer atomic.StoreInt32(&d.synchronizing, 0)
 
-	// When a synchronization attempt is made while the queue still
-	// contains items we abort the sync attempt
-	if done, pend := d.queue.Size(); done+pend > 0 {
+	// Abort if the queue still contains some leftover data
+	if _, cached := d.queue.Size(); cached > 0 {
 		return errPendingQueue
 	}
-
-	// Fetch the peer using the id or throw an error if the peer couldn't be found
+	// Retrieve the origin peer and initiate the downloading process
 	p := d.peers[id]
 	if p == nil {
 		return errUnknownPeer
 	}
-
-	// Get the hash from the peer and initiate the downloading progress.
-	err := d.getFromPeer(p, hash, false)
-	if err != nil {
-		return err
-	}
-
-	return nil
-}
-
-// Done lets the downloader know that whatever previous hashes were taken
-// are processed. If the block count reaches zero and done is called
-// we reset the queue for the next batch of incoming hashes and blocks.
-func (d *Downloader) Done() {
-	d.queue.Done()
+	return d.getFromPeer(p, hash, false)
 }
 
 // TakeBlocks takes blocks from the queue and yields them to the blockTaker handler
@@ -176,6 +158,7 @@ func (d *Downloader) Has(hash common.Hash) bool {
 }
 
 func (d *Downloader) getFromPeer(p *peer, hash common.Hash, ignoreInitial bool) (err error) {
+
 	d.activePeer = p.id
 	defer func() {
 		// reset on error
@@ -184,7 +167,7 @@ func (d *Downloader) getFromPeer(p *peer, hash common.Hash, ignoreInitial bool)
 		}
 	}()
 
-	glog.V(logger.Detail).Infoln("Synchronising with the network using:", p.id)
+	glog.V(logger.Debug).Infoln("Synchronizing with the network using:", p.id)
 	// Start the fetcher. This will block the update entirely
 	// interupts need to be send to the appropriate channels
 	// respectively.
@@ -200,20 +183,13 @@ func (d *Downloader) getFromPeer(p *peer, hash common.Hash, ignoreInitial bool)
 		return err
 	}
 
-	glog.V(logger.Detail).Infoln("Sync completed")
+	glog.V(logger.Debug).Infoln("Synchronization completed")
 
 	return nil
 }
 
 // XXX Make synchronous
 func (d *Downloader) startFetchingHashes(p *peer, h common.Hash, ignoreInitial bool) error {
-	atomic.StoreInt32(&d.fetchingHashes, 1)
-	defer atomic.StoreInt32(&d.fetchingHashes, 0)
-
-	if d.queue.Has(h) { // TODO: Is this possible? Shouldn't queue be empty for startFetchingHashes to be even called?
-		return errAlreadyInPool
-	}
-
 	glog.V(logger.Debug).Infof("Downloading hashes (%x) from %s", h[:4], p.id)
 
 	start := time.Now()
@@ -312,10 +288,8 @@ out:
 }
 
 func (d *Downloader) startFetchingBlocks(p *peer) error {
-	glog.V(logger.Detail).Infoln("Downloading", d.queue.Pending(), "block(s)")
+	glog.V(logger.Debug).Infoln("Downloading", d.queue.Pending(), "block(s)")
 
-	atomic.StoreInt32(&d.downloadingBlocks, 1)
-	defer atomic.StoreInt32(&d.downloadingBlocks, 0)
 	// Defer the peer reset. This will empty the peer requested set
 	// and makes sure there are no lingering peers with an incorrect
 	// state
@@ -439,19 +413,3 @@ func (d *Downloader) AddHashes(id string, hashes []common.Hash) error {
 
 	return nil
 }
-
-func (d *Downloader) isFetchingHashes() bool {
-	return atomic.LoadInt32(&d.fetchingHashes) == 1
-}
-
-func (d *Downloader) isDownloadingBlocks() bool {
-	return atomic.LoadInt32(&d.downloadingBlocks) == 1
-}
-
-func (d *Downloader) isBusy() bool {
-	return d.isFetchingHashes() || d.isDownloadingBlocks()
-}
-
-func (d *Downloader) IsBusy() bool {
-	return d.isBusy()
-}