mmap_span: Avoid allocating the span slice on every use

cmd/torrent-verify/main.go

@@ -33,7 +33,7 @@ func main() {
 		log.Print(err)
 	}
 	defer devZero.Close()
-	var mMapSpan mmap_span.MMapSpan
+	var mMapSpan *mmap_span.MMapSpan
 	for _, file := range metaInfo.Info.Files {
 		filename := filepath.Join(append([]string{*dirPath, metaInfo.Info.Name}, file.Path...)...)
 		osFile, err := os.Open(filename)
@@ -53,7 +53,7 @@ func main() {
 			log.Printf("file mmap has wrong size: %#v", filename)
 		}
 		osFile.Close()
-		mMapSpan = append(mMapSpan, goMMap)
+		mMapSpan.Append(goMMap)
 	}
 	log.Println(len(metaInfo.Info.Files))
 	log.Println(mMapSpan.Size())

misc.go

@@ -125,7 +125,8 @@ func upvertedSingleFileInfoFiles(info *metainfo.Info) []metainfo.FileInfo {
 	return []metainfo.FileInfo{{Length: info.Length, Path: nil}}
 }
 
-func mmapTorrentData(md *metainfo.Info, location string) (mms mmap_span.MMapSpan, err error) {
+func mmapTorrentData(md *metainfo.Info, location string) (mms *mmap_span.MMapSpan, err error) {
+	mms = &mmap_span.MMapSpan{}
 	defer func() {
 		if err != nil {
 			mms.Close()
@@ -170,7 +171,7 @@ func mmapTorrentData(md *metainfo.Info, location string) (mms mmap_span.MMapSpan
 			if int64(len(mMap)) != miFile.Length {
 				panic("mmap has wrong length")
 			}
-			mms = append(mms, mMap)
+			mms.Append(mMap)
 		}()
 		if err != nil {
 			return

mmap_span/mmap_span.go

@@ -14,30 +14,29 @@ func (me segment) Size() int64 {
 	return int64(len(me.MMap))
 }
 
-type MMapSpan []gommap.MMap
+type MMapSpan struct {
+	span
+}
 
-func (me MMapSpan) span() (s span) {
-	for _, mmap := range me {
-		s = append(s, segment{mmap})
-	}
-	return
+func (me *MMapSpan) Append(mmap gommap.MMap) {
+	me.span = append(me.span, segment{mmap})
 }
 
 func (me MMapSpan) Close() {
-	for _, mMap := range me {
-		mMap.UnsafeUnmap()
+	for _, mMap := range me.span {
+		mMap.(segment).UnsafeUnmap()
 	}
 }
 
 func (me MMapSpan) Size() (ret int64) {
-	for _, seg := range me.span() {
+	for _, seg := range me.span {
 		ret += seg.Size()
 	}
 	return
 }
 
 func (me MMapSpan) ReadAt(p []byte, off int64) (n int, err error) {
-	me.span().ApplyTo(off, func(intervalOffset int64, interval sizer) (stop bool) {
+	me.ApplyTo(off, func(intervalOffset int64, interval sizer) (stop bool) {
 		_n := copy(p, interval.(segment).MMap[intervalOffset:])
 		p = p[_n:]
 		n += _n
@@ -50,7 +49,7 @@ func (me MMapSpan) ReadAt(p []byte, off int64) (n int, err error) {
 }
 
 func (me MMapSpan) WriteSectionTo(w io.Writer, off, n int64) (written int64, err error) {
-	me.span().ApplyTo(off, func(intervalOffset int64, interval sizer) (stop bool) {
+	me.ApplyTo(off, func(intervalOffset int64, interval sizer) (stop bool) {
 		var _n int
 		p := interval.(segment).MMap[intervalOffset:]
 		if n < int64(len(p)) {
@@ -68,7 +67,7 @@ func (me MMapSpan) WriteSectionTo(w io.Writer, off, n int64) (written int64, err
 }
 
 func (me MMapSpan) WriteAt(p []byte, off int64) (n int, err error) {
-	me.span().ApplyTo(off, func(iOff int64, i sizer) (stop bool) {
+	me.ApplyTo(off, func(iOff int64, i sizer) (stop bool) {
 		mMap := i.(segment)
 		_n := copy(mMap.MMap[iOff:], p)
 		// err = mMap.Sync(gommap.MS_ASYNC)

torrent.go

@@ -60,7 +60,7 @@ type torrent struct {
 	length                      int64
 	// Prevent mutations to Data memory maps while in use as they're not safe.
 	dataLock sync.RWMutex
-	Data     mmap_span.MMapSpan
+	Data     *mmap_span.MMapSpan
 
 	Info *MetaInfo
 	// Active peer connections.
@@ -459,8 +459,10 @@ func (t *torrent) Close() (err error) {
 	t.CeaseNetworking()
 	close(t.closing)
 	t.dataLock.Lock()
-	t.Data.Close()
-	t.Data = nil
+	if t.Data != nil {
+		t.Data.Close()
+		t.Data = nil
+	}
 	t.dataLock.Unlock()
 	for _, conn := range t.Conns {
 		conn.Close()