Store chunk data without holding client lock

client.go

@@ -1432,6 +1432,7 @@ another:
 
 func (me *Client) sendChunk(t *torrent, c *connection, r request) error {
 	b := make([]byte, r.Length)
+	t.Pieces[r.Index].pendingWrites.Wait()
 	p := t.Info.Piece(int(r.Index))
 	n, err := dataReadAt(t.data, b, p.Offset()+int64(r.Begin))
 	if err != nil {
@@ -2523,12 +2524,18 @@ func (me *Client) downloadedChunk(t *torrent, c *connection, msg *pp.Message) er
 
 	me.upload(t, c)
 
-	// Write the chunk out.
-	err := t.writeChunk(int(msg.Index), int64(msg.Begin), msg.Piece)
-	if err != nil {
-		log.Printf("error writing chunk: %s", err)
-		return nil
-	}
+	piece.pendingWrites.Add(1)
+	go func() {
+		defer piece.pendingWrites.Done()
+		// Write the chunk out.
+		tr := perf.NewTimer()
+		err := t.writeChunk(int(msg.Index), int64(msg.Begin), msg.Piece)
+		if err != nil {
+			log.Printf("error writing chunk: %s", err)
+			return
+		}
+		tr.Stop("write chunk")
+	}()
 
 	// log.Println("got chunk", req)
 	piece.Event.Broadcast()

piece.go

@@ -30,6 +30,7 @@ type piece struct {
 	EverHashed        bool
 	Event             sync.Cond
 	Priority          piecePriority
+	pendingWrites     sync.WaitGroup
 }
 
 func (p *piece) pendingChunk(cs chunkSpec, chunkSize pp.Integer) bool {

reader.go

@@ -121,6 +121,14 @@ again:
 	avail := r.available(pos, int64(len(b)))
 	// log.Println("available", avail)
 	b1 := b[:avail]
+	pi := int(pos / r.t.Info().PieceLength)
+	tp := r.t.torrent.Pieces[pi]
+	ip := r.t.Info().Piece(pi)
+	po := pos % ip.Length()
+	if int64(len(b1)) > ip.Length()-po {
+		b1 = b1[:ip.Length()-po]
+	}
+	tp.pendingWrites.Wait()
 	n, err = dataReadAt(r.t.data, b1, pos)
 	if n != 0 {
 		err = nil

torrent.go

@@ -638,6 +638,8 @@ func (t *torrent) pieceLength(piece int) (len_ pp.Integer) {
 
 func (t *torrent) hashPiece(piece pp.Integer) (ps pieceSum) {
 	hash := pieceHash.New()
+	p := t.Pieces[piece]
+	p.pendingWrites.Wait()
 	t.data.WriteSectionTo(hash, int64(piece)*t.Info.PieceLength, t.Info.PieceLength)
 	util.CopyExact(ps[:], hash.Sum(nil))
 	return