Do t.storage.Flush() on torrent completion, and on storage.Close()

mmap_span/mmap_span.go

@@ -19,11 +19,27 @@ func (ms *MMapSpan) Append(mMap mmap.MMap) {
 	ms.mMaps = append(ms.mMaps, mMap)
 }
 
+func (ms *MMapSpan) Flush() (errs []error) {
+	ms.mu.Lock()
+	defer ms.mu.Unlock()
+	for _, mMap := range ms.mMaps {
+		err := mMap.Flush()
+		if err != nil {
+			errs = append(errs, err)
+		}
+	}
+	return
+}
+
 func (ms *MMapSpan) Close() (errs []error) {
 	ms.mu.Lock()
 	defer ms.mu.Unlock()
 	for _, mMap := range ms.mMaps {
-		err := mMap.Unmap()
+		err := mMap.Flush()
+		if err != nil {
+			errs = append(errs, err)
+		}
+		err = mMap.Unmap()
 		if err != nil {
 			errs = append(errs, err)
 		}

storage/interface.go

@@ -22,6 +22,7 @@ type TorrentCapacity *func() (cap int64, capped bool)
 type TorrentImpl struct {
 	Piece func(p metainfo.Piece) PieceImpl
 	Close func() error
+	Flush func() error
 	// Storages that share the same space, will provide equal pointers. The function is called once
 	// to determine the storage for torrents sharing the same function pointer, and mutated in
 	// place.

storage/mmap.go

@@ -41,7 +41,7 @@ func (s *mmapClientImpl) OpenTorrent(info *metainfo.Info, infoHash metainfo.Hash
 		span:     span,
 		pc:       s.pc,
 	}
-	return TorrentImpl{Piece: t.Piece, Close: t.Close}, err
+	return TorrentImpl{Piece: t.Piece, Close: t.Close, Flush: t.Flush}, err
 }
 
 func (s *mmapClientImpl) Close() error {
@@ -71,6 +71,13 @@ func (ts *mmapTorrentStorage) Close() error {
 	}
 	return nil
 }
+func (ts *mmapTorrentStorage) Flush() error {
+	errs := ts.span.Flush()
+	if len(errs) > 0 {
+		return errs[0]
+	}
+	return nil
+}
 
 type mmapStoragePiece struct {
 	pc PieceCompletionGetSetter

torrent.go

@@ -2461,7 +2461,11 @@ func (t *Torrent) pieceRequestIndexOffset(piece pieceIndex) RequestIndex {
 }
 
 func (t *Torrent) updateComplete() {
+	before := t.Complete.Bool()
 	t.Complete.SetBool(t.haveAllPieces())
+	if !before && t.storage.Flush != nil && t.Complete.Bool() {
+		_ = t.storage.Flush()
+	}
 }
 
 func (t *Torrent) cancelRequest(r RequestIndex) *Peer {