Remove sync.Cond from piece

It's not trivial to ensure that anyone waiting on the piece Cond will wake on events like the torrent being dropped from the client.

client.go

@@ -1923,7 +1923,7 @@ func (cl *Client) setStorage(t *torrent, td Data) (err error) {
 type TorrentDataOpener func(*metainfo.Info) Data
 
 func (cl *Client) setMetaData(t *torrent, md *metainfo.Info, bytes []byte) (err error) {
-	err = t.setMetadata(md, bytes, &cl.mu)
+	err = t.setMetadata(md, bytes)
 	if err != nil {
 		return
 	}
@@ -2590,7 +2590,7 @@ func (me *Client) downloadedChunk(t *torrent, c *connection, msg *pp.Message) er
 	c.peerTouchedPieces[int(req.Index)] = struct{}{}
 
 	// log.Println("got chunk", req)
-	piece.Event.Broadcast()
+	me.event.Broadcast()
 	defer t.publishPieceChange(int(req.Index))
 	// Record that we have the chunk.
 	piece.unpendChunkIndex(chunkIndex(req.chunkSpec, t.chunkSize))
@@ -2662,7 +2662,7 @@ func (me *Client) pieceChanged(t *torrent, piece int) {
 	correct := t.pieceComplete(piece)
 	p := &t.Pieces[piece]
 	defer t.publishPieceChange(piece)
-	defer p.Event.Broadcast()
+	defer me.event.Broadcast()
 	if correct {
 		p.Priority = PiecePriorityNone
 		p.PendingChunkSpecs = nil

client_test.go

@@ -99,7 +99,7 @@ func TestTorrentInitialState(t *testing.T) {
 		t.Fatal(err)
 	}
 	tor.chunkSize = 2
-	err = tor.setMetadata(&mi.Info.Info, mi.Info.Bytes, nil)
+	err = tor.setMetadata(&mi.Info.Info, mi.Info.Bytes)
 	if err != nil {
 		t.Fatal(err)
 	}

piece.go

@@ -28,7 +28,6 @@ type piece struct {
 	Hashing           bool
 	QueuedForHash     bool
 	EverHashed        bool
-	Event             sync.Cond
 	Priority          piecePriority
 	PublicPieceState  PieceState
 

reader.go

@@ -75,7 +75,7 @@ func (r *Reader) available(off, max int64) (ret int64) {
 }
 
 func (r *Reader) waitReadable(off int64) {
-	r.t.Pieces[off/int64(r.t.usualPieceSize())].Event.Wait()
+	r.t.cl.event.Wait()
 }
 
 func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {

t.go

@@ -2,6 +2,7 @@ package torrent
 
 import (
 	"github.com/anacrolix/missinggo/pubsub"
+
 	"github.com/anacrolix/torrent/metainfo"
 )
 

torrent.go

@@ -232,7 +232,7 @@ func infoPieceHashes(info *metainfo.Info) (ret []string) {
 }
 
 // Called when metadata for a torrent becomes available.
-func (t *torrent) setMetadata(md *metainfo.Info, infoBytes []byte, eventLocker sync.Locker) (err error) {
+func (t *torrent) setMetadata(md *metainfo.Info, infoBytes []byte) (err error) {
 	err = validateInfo(md)
 	if err != nil {
 		err = fmt.Errorf("bad info: %s", err)
@@ -249,7 +249,6 @@ func (t *torrent) setMetadata(md *metainfo.Info, infoBytes []byte, eventLocker s
 	t.Pieces = make([]piece, len(hashes))
 	for i, hash := range hashes {
 		piece := &t.Pieces[i]
-		piece.Event.L = eventLocker
 		piece.noPendingWrites.L = &piece.pendingWritesMutex
 		missinggo.CopyExact(piece.Hash[:], hash)
 	}