Rework Reader position changes affecting piece priorities

Torrent.updatePiecePriorities is always followed by Torrent.piecePriorityChanged, so move it into the former function. Also drop the separate mutex for Reader, and add a missing Reader.posChanged call.

client.go

@@ -1715,10 +1715,7 @@ func (cl *Client) pieceChanged(t *Torrent, piece int) {
 	} else {
 		cl.onFailedPiece(t, piece)
 	}
-	if t.updatePiecePriority(piece) {
-		t.piecePriorityChanged(piece)
-	}
-	t.publishPieceChange(piece)
+	t.updatePiecePriority(piece)
 }
 
 func (cl *Client) verifyPiece(t *Torrent, piece int) {
@@ -1731,7 +1728,6 @@ func (cl *Client) verifyPiece(t *Torrent, piece int) {
 	p.QueuedForHash = false
 	if t.closed.IsSet() || t.pieceComplete(piece) {
 		t.updatePiecePriority(piece)
-		t.publishPieceChange(piece)
 		return
 	}
 	p.Hashing = true

reader.go

@@ -21,7 +21,7 @@ type Reader struct {
 
 	// Required when modifying pos and readahead, or reading them without
 	// opMu.
-	mu        sync.Mutex
+	mu        sync.Locker
 	pos       int64
 	readahead int64
 }
@@ -128,6 +128,7 @@ func (r *Reader) ReadContext(b []byte, ctx context.Context) (n int, err error) {
 		n += n1
 		r.mu.Lock()
 		r.pos += int64(n1)
+		r.posChanged()
 		r.mu.Unlock()
 	}
 	if r.pos >= r.t.length {
@@ -192,8 +193,6 @@ func (r *Reader) Close() error {
 }
 
 func (r *Reader) posChanged() {
-	r.t.cl.mu.Lock()
-	defer r.t.cl.mu.Unlock()
 	r.t.readersChanged()
 }
 
@@ -202,6 +201,7 @@ func (r *Reader) Seek(off int64, whence int) (ret int64, err error) {
 	defer r.opMu.Unlock()
 
 	r.mu.Lock()
+	defer r.mu.Unlock()
 	switch whence {
 	case os.SEEK_SET:
 		r.pos = off
@@ -213,7 +213,6 @@ func (r *Reader) Seek(off int64, whence int) (ret int64, err error) {
 		err = errors.New("bad whence")
 	}
 	ret = r.pos
-	r.mu.Unlock()
 
 	r.posChanged()
 	return

t.go

@@ -32,6 +32,7 @@ func (t *Torrent) Info() *metainfo.Info {
 // the data requested is actually available.
 func (t *Torrent) NewReader() (ret *Reader) {
 	ret = &Reader{
+		mu:        &t.cl.mu,
 		t:         t,
 		readahead: 5 * 1024 * 1024,
 	}

torrent.go

@@ -97,7 +97,9 @@ type Torrent struct {
 	// Set when .Info is obtained.
 	gotMetainfo missinggo.Event
 
-	readers map[*Reader]struct{}
+	readers               map[*Reader]struct{}
+	readerNowPieces       bitmap.Bitmap
+	readerReadaheadPieces bitmap.Bitmap
 
 	// The indexes of pieces we want with normal priority, that aren't
 	// currently available.
@@ -824,6 +826,7 @@ func (t *Torrent) forUrgentPieces(f func(piece int) (again bool)) (all bool) {
 }
 
 func (t *Torrent) readersChanged() {
+	t.readerNowPieces, t.readerReadaheadPieces = t.readerPiecePriorities()
 	t.updatePiecePriorities()
 }
 
@@ -841,42 +844,21 @@ func (t *Torrent) piecePriorityChanged(piece int) {
 	t.publishPieceChange(piece)
 }
 
-func (t *Torrent) updatePiecePriority(piece int) bool {
+func (t *Torrent) updatePiecePriority(piece int) {
 	p := &t.pieces[piece]
 	newPrio := t.piecePriorityUncached(piece)
 	if newPrio == p.priority {
-		return false
+		return
 	}
 	p.priority = newPrio
-	return true
+	t.piecePriorityChanged(piece)
 }
 
 // Update all piece priorities in one hit. This function should have the same
 // output as updatePiecePriority, but across all pieces.
 func (t *Torrent) updatePiecePriorities() {
-	newPrios := make([]piecePriority, t.numPieces())
-	t.pendingPieces.IterTyped(func(piece int) (more bool) {
-		newPrios[piece] = PiecePriorityNormal
-		return true
-	})
-	t.forReaderOffsetPieces(func(begin, end int) (next bool) {
-		if begin < end {
-			newPrios[begin].Raise(PiecePriorityNow)
-		}
-		for i := begin + 1; i < end; i++ {
-			newPrios[i].Raise(PiecePriorityReadahead)
-		}
-		return true
-	})
-	t.completedPieces.IterTyped(func(piece int) (more bool) {
-		newPrios[piece] = PiecePriorityNone
-		return true
-	})
-	for i, prio := range newPrios {
-		if prio != t.pieces[i].priority {
-			t.pieces[i].priority = prio
-			t.piecePriorityChanged(i)
-		}
+	for i := range t.pieces {
+		t.updatePiecePriority(i)
 	}
 }
 
@@ -904,9 +886,9 @@ func (t *Torrent) byteRegionPieces(off, size int64) (begin, end int) {
 // callers depend on this method to enumerate readers.
 func (t *Torrent) forReaderOffsetPieces(f func(begin, end int) (more bool)) (all bool) {
 	for r := range t.readers {
-		r.mu.Lock()
+		// r.mu.Lock()
 		pos, readahead := r.pos, r.readahead
-		r.mu.Unlock()
+		// r.mu.Unlock()
 		if readahead < 1 {
 			readahead = 1
 		}
@@ -928,25 +910,23 @@ func (t *Torrent) piecePriority(piece int) piecePriority {
 	return t.pieces[piece].priority
 }
 
-func (t *Torrent) piecePriorityUncached(piece int) (ret piecePriority) {
-	ret = PiecePriorityNone
+func (t *Torrent) piecePriorityUncached(piece int) piecePriority {
 	if t.pieceComplete(piece) {
-		return
+		return PiecePriorityNone
+	}
+	if t.readerNowPieces.Contains(piece) {
+		return PiecePriorityNow
+	}
+	// if t.readerNowPieces.Contains(piece - 1) {
+	// 	return PiecePriorityNext
+	// }
+	if t.readerReadaheadPieces.Contains(piece) {
+		return PiecePriorityReadahead
 	}
 	if t.pendingPieces.Contains(piece) {
-		ret = PiecePriorityNormal
+		return PiecePriorityNormal
 	}
-	raiseRet := ret.Raise
-	t.forReaderOffsetPieces(func(begin, end int) (again bool) {
-		if piece == begin {
-			raiseRet(PiecePriorityNow)
-		}
-		if begin <= piece && piece < end {
-			raiseRet(PiecePriorityReadahead)
-		}
-		return true
-	})
-	return
+	return PiecePriorityNone
 }
 
 func (t *Torrent) pendPiece(piece int) {
@@ -957,10 +937,7 @@ func (t *Torrent) pendPiece(piece int) {
 		return
 	}
 	t.pendingPieces.Add(piece)
-	if !t.updatePiecePriority(piece) {
-		return
-	}
-	t.piecePriorityChanged(piece)
+	t.updatePiecePriority(piece)
 }
 
 func (t *Torrent) getCompletedPieces() (ret bitmap.Bitmap) {
@@ -1075,6 +1052,17 @@ func (t *Torrent) readerPieces() (ret bitmap.Bitmap) {
 	return
 }
 
+func (t *Torrent) readerPiecePriorities() (now, readahead bitmap.Bitmap) {
+	t.forReaderOffsetPieces(func(begin, end int) bool {
+		if end > begin {
+			now.Add(begin)
+			readahead.AddRange(begin+1, end)
+		}
+		return true
+	})
+	return
+}
+
 func (t *Torrent) needData() bool {
 	if t.closed.IsSet() {
 		return false