Add pending write helpers

client.go

@@ -1357,11 +1357,7 @@ func (me *Client) sendChunk(t *torrent, c *connection, r request) error {
 	c.chunksSent++
 	b := make([]byte, r.Length)
 	tp := &t.Pieces[r.Index]
-	tp.pendingWritesMutex.Lock()
+	tp.waitNoPendingWrites()
-	for tp.pendingWrites != 0 {
-		tp.noPendingWrites.Wait()
-	}
-	tp.pendingWritesMutex.Unlock()
 	p := t.Info.Piece(int(r.Index))
 	n, err := dataReadAt(t.data, b, p.Offset()+int64(r.Begin))
 	if err != nil {

piece.go

@@ -92,3 +92,29 @@ func (p *piece) shuffledPendingChunkSpecs(t *torrent, piece int) (css []chunkSpe
 	}
 	return
 }
+
+func (p *piece) incrementPendingWrites() {
+	p.pendingWritesMutex.Lock()
+	p.pendingWrites++
+	p.pendingWritesMutex.Unlock()
+}
+
+func (p *piece) decrementPendingWrites() {
+	p.pendingWritesMutex.Lock()
+	if p.pendingWrites == 0 {
+		panic("assertion")
+	}
+	p.pendingWrites--
+	if p.pendingWrites == 0 {
+		p.noPendingWrites.Broadcast()
+	}
+	p.pendingWritesMutex.Unlock()
+}
+
+func (p *piece) waitNoPendingWrites() {
+	p.pendingWritesMutex.Lock()
+	for p.pendingWrites != 0 {
+		p.noPendingWrites.Wait()
+	}
+	p.pendingWritesMutex.Unlock()
+}

reader.go

@@ -118,11 +118,7 @@ again:
 	if int64(len(b1)) > ip.Length()-po {
 		b1 = b1[:ip.Length()-po]
 	}
-	tp.pendingWritesMutex.Lock()
+	tp.waitNoPendingWrites()
-	for tp.pendingWrites != 0 {
-		tp.noPendingWrites.Wait()
-	}
-	tp.pendingWritesMutex.Unlock()
 	n, err = dataReadAt(r.t.torrent.data, b1, pos)
 	if n != 0 {
 		err = nil

torrent.go

@@ -645,11 +645,7 @@ func (t *torrent) pieceLength(piece int) (len_ pp.Integer) {
 func (t *torrent) hashPiece(piece int) (ps pieceSum) {
 	hash := pieceHash.New()
 	p := &t.Pieces[piece]
-	p.pendingWritesMutex.Lock()
+	p.waitNoPendingWrites()
-	for p.pendingWrites != 0 {
-		p.noPendingWrites.Wait()
-	}
-	p.pendingWritesMutex.Unlock()
 	pl := t.Info.Piece(int(piece)).Length()
 	n, err := t.data.WriteSectionTo(hash, int64(piece)*t.Info.PieceLength, pl)
 	if err != nil {