X-Git-Url: http://www.git.stargrave.org/?a=blobdiff_plain;f=reader.go;h=4b20206cbf2ecc675ccde147cecc278ebc688040;hb=HEAD;hp=965fbdf8beb643de5c9a5464efbb30a253a0f55e;hpb=e6da640bb2b5de5ff43689cdbc517125976b8073;p=btrtrc.git

diff --git a/reader.go b/reader.go
index 965fbdf8..4b20206c 100644
--- a/reader.go
+++ b/reader.go
@@ -8,19 +8,21 @@ import (
 	"sync"
 
 	"github.com/anacrolix/log"
-	"github.com/anacrolix/missinggo"
+	"github.com/anacrolix/missinggo/v2"
 )
 
 // Accesses Torrent data via a Client. Reads block until the data is available. Seeks and readahead
-// also drive Client behaviour.
+// also drive Client behaviour. Not safe for concurrent use.
 type Reader interface {
-	io.Reader
-	io.Seeker
-	io.Closer
+	io.ReadSeekCloser
 	missinggo.ReadContexter
 	// Configure the number of bytes ahead of a read that should also be prioritized in preparation
-	// for further reads.
+	// for further reads. Overridden by non-nil readahead func, see SetReadaheadFunc.
 	SetReadahead(int64)
+	// If non-nil, the provided function is called when the implementation needs to know the
+	// readahead for the current reader. Calls occur during Reads and Seeks, and while the Client is
+	// locked.
+	SetReadaheadFunc(ReadaheadFunc)
 	// Don't wait for pieces to complete and be verified. Read calls return as soon as they can when
 	// the underlying chunks become available.
 	SetResponsive()
@@ -31,25 +33,40 @@ type pieceRange struct {
 	begin, end pieceIndex
 }
 
+type ReadaheadContext struct {
+	ContiguousReadStartPos int64
+	CurrentPos             int64
+}
+
+// Returns the desired readahead for a Reader.
+type ReadaheadFunc func(ReadaheadContext) int64
+
 type reader struct {
-	t          *Torrent
-	responsive bool
+	t *Torrent
 	// Adjust the read/seek window to handle Readers locked to File extents and the like.
 	offset, length int64
-	// Ensure operations that change the position are exclusive, like Read() and Seek().
-	opMu sync.Mutex
 
-	// Required when modifying pos and readahead, or reading them without opMu.
-	mu        sync.Locker
-	pos       int64
-	readahead int64
+	// Function to dynamically calculate readahead. If nil, readahead is static.
+	readaheadFunc ReadaheadFunc
+
+	// Required when modifying pos and readahead.
+	mu sync.Locker
+
+	readahead, pos int64
+	// Position that reads have continued contiguously from.
+	contiguousReadStartPos int64
 	// The cached piece range this reader wants downloaded. The zero value corresponds to nothing.
 	// We cache this so that changes can be detected, and bubbled up to the Torrent only as
 	// required.
 	pieces pieceRange
+
+	// Reads have been initiated since the last seek. This is used to prevent readaheads occurring
+	// after a seek or with a new reader at the starting position.
+	reading    bool
+	responsive bool
 }
 
-var _ io.ReadCloser = (*reader)(nil)
+var _ io.ReadSeekCloser = (*reader)(nil)
 
 func (r *reader) SetResponsive() {
 	r.responsive = true
@@ -65,10 +82,16 @@ func (r *reader) SetNonResponsive() {
 func (r *reader) SetReadahead(readahead int64) {
 	r.mu.Lock()
 	r.readahead = readahead
+	r.readaheadFunc = nil
+	r.posChanged()
 	r.mu.Unlock()
-	r.t.cl.lock()
-	defer r.t.cl.unlock()
+}
+
+func (r *reader) SetReadaheadFunc(f ReadaheadFunc) {
+	r.mu.Lock()
+	r.readaheadFunc = f
 	r.posChanged()
+	r.mu.Unlock()
 }
 
 // How many bytes are available to read. Max is the most we could require.
@@ -97,19 +120,23 @@ func (r *reader) available(off, max int64) (ret int64) {
 	return
 }
 
-func (r *reader) waitReadable(off int64) {
-	// We may have been sent back here because we were told we could read but it failed.
-	r.t.cl.event.Wait()
-}
-
 // Calculates the pieces this reader wants downloaded, ignoring the cached value at r.pieces.
 func (r *reader) piecesUncached() (ret pieceRange) {
 	ra := r.readahead
+	if r.readaheadFunc != nil {
+		ra = r.readaheadFunc(ReadaheadContext{
+			ContiguousReadStartPos: r.contiguousReadStartPos,
+			CurrentPos:             r.pos,
+		})
+	}
 	if ra < 1 {
 		// Needs to be at least 1, because [x, x) means we don't want
 		// anything.
 		ra = 1
 	}
+	if !r.reading {
+		ra = 0
+	}
 	if ra > r.length-r.pos {
 		ra = r.length - r.pos
 	}
@@ -122,29 +149,17 @@ func (r *reader) Read(b []byte) (n int, err error) {
 }
 
 func (r *reader) ReadContext(ctx context.Context, b []byte) (n int, err error) {
-	// This is set under the Client lock if the Context is canceled. I think we coordinate on a
-	// separate variable so as to avoid false negatives with race conditions due to Contexts being
-	// synchronized.
-	var ctxErr error
-	if ctx.Done() != nil {
-		ctx, cancel := context.WithCancel(ctx)
-		// Abort the goroutine when the function returns.
-		defer cancel()
-		go func() {
-			<-ctx.Done()
-			r.t.cl.lock()
-			ctxErr = ctx.Err()
-			r.t.tickleReaders()
-			r.t.cl.unlock()
-		}()
+	if len(b) > 0 {
+		r.reading = true
+		// TODO: Rework reader piece priorities so we don't have to push updates in to the Client
+		// and take the lock here.
+		r.mu.Lock()
+		r.posChanged()
+		r.mu.Unlock()
 	}
-	// Hmmm, if a Read gets stuck, this means you can't change position for other purposes. That
-	// seems reasonable, but unusual.
-	r.opMu.Lock()
-	defer r.opMu.Unlock()
-	n, err = r.readOnceAt(b, r.pos, &ctxErr)
+	n, err = r.readOnceAt(ctx, b, r.pos)
 	if n == 0 {
-		if err == nil {
+		if err == nil && len(b) > 0 {
 			panic("expected error")
 		} else {
 			return
@@ -163,32 +178,44 @@ func (r *reader) ReadContext(ctx context.Context, b []byte) (n int, err error) {
 	return
 }
 
+var closedChan = make(chan struct{})
+
+func init() {
+	close(closedChan)
+}
+
 // Wait until some data should be available to read. Tickles the client if it isn't. Returns how
 // much should be readable without blocking.
-func (r *reader) waitAvailable(pos, wanted int64, ctxErr *error, wait bool) (avail int64, err error) {
-	r.t.cl.lock()
-	defer r.t.cl.unlock()
+func (r *reader) waitAvailable(ctx context.Context, pos, wanted int64, wait bool) (avail int64, err error) {
+	t := r.t
 	for {
+		r.t.cl.rLock()
 		avail = r.available(pos, wanted)
+		readerCond := t.piece(int((r.offset + pos) / t.info.PieceLength)).readerCond.Signaled()
+		r.t.cl.rUnlock()
 		if avail != 0 {
 			return
 		}
-		if r.t.closed.IsSet() {
+		var dontWait <-chan struct{}
+		if !wait || wanted == 0 {
+			dontWait = closedChan
+		}
+		select {
+		case <-r.t.closed.Done():
 			err = errors.New("torrent closed")
 			return
-		}
-		if *ctxErr != nil {
-			err = *ctxErr
+		case <-ctx.Done():
+			err = ctx.Err()
 			return
-		}
-		if r.t.dataDownloadDisallowed || !r.t.networkingEnabled {
-			err = errors.New("downloading disabled and data not already available")
+		case <-r.t.dataDownloadDisallowed.On():
+			err = errors.New("torrent data downloading disabled")
+		case <-r.t.networkingEnabled.Off():
+			err = errors.New("torrent networking disabled")
 			return
-		}
-		if !wait {
+		case <-dontWait:
 			return
+		case <-readerCond:
 		}
-		r.waitReadable(pos)
 	}
 }
 
@@ -199,14 +226,14 @@ func (r *reader) torrentOffset(readerPos int64) int64 {
 }
 
 // Performs at most one successful read to torrent storage.
-func (r *reader) readOnceAt(b []byte, pos int64, ctxErr *error) (n int, err error) {
+func (r *reader) readOnceAt(ctx context.Context, b []byte, pos int64) (n int, err error) {
 	if pos >= r.length {
 		err = io.EOF
 		return
 	}
 	for {
 		var avail int64
-		avail, err = r.waitAvailable(pos, int64(len(b)), ctxErr, n == 0)
+		avail, err = r.waitAvailable(ctx, pos, int64(len(b)), n == 0)
 		if avail == 0 {
 			return
 		}
@@ -218,32 +245,45 @@ func (r *reader) readOnceAt(b []byte, pos int64, ctxErr *error) (n int, err erro
 			err = nil
 			return
 		}
-		r.t.cl.lock()
-		// TODO: Just reset pieces in the readahead window. This might help
-		// prevent thrashing with small caches and file and piece priorities.
-		r.log(log.Fstr("error reading torrent %s piece %d offset %d, %d bytes: %v",
-			r.t.infoHash.HexString(), firstPieceIndex, firstPieceOffset, len(b1), err))
-		if !r.t.updatePieceCompletion(firstPieceIndex) {
-			r.log(log.Fstr("piece %d completion unchanged", firstPieceIndex))
-		}
-		// Update the rest of the piece completions in the readahead window, without alerting to
-		// changes (since only the first piece, the one above, could have generated the read error
-		// we're currently handling).
-		if r.pieces.begin != firstPieceIndex {
-			panic(fmt.Sprint(r.pieces.begin, firstPieceIndex))
-		}
-		for index := r.pieces.begin + 1; index < r.pieces.end; index++ {
-			r.t.updatePieceCompletion(index)
+		if r.t.closed.IsSet() {
+			err = fmt.Errorf("reading from closed torrent: %w", err)
+			return
 		}
-		r.t.cl.unlock()
+		r.t.cl.lock()
+		// I think there's a panic here caused by the Client being closed before obtaining this
+		// lock. TestDropTorrentWithMmapStorageWhileHashing seems to tickle occasionally in CI.
+		func() {
+			// Just add exceptions already.
+			defer r.t.cl.unlock()
+			if r.t.closed.IsSet() {
+				// Can't update because Torrent's piece order is removed from Client.
+				return
+			}
+			// TODO: Just reset pieces in the readahead window. This might help
+			// prevent thrashing with small caches and file and piece priorities.
+			r.log(log.Fstr("error reading torrent %s piece %d offset %d, %d bytes: %v",
+				r.t.infoHash.HexString(), firstPieceIndex, firstPieceOffset, len(b1), err))
+			if !r.t.updatePieceCompletion(firstPieceIndex) {
+				r.log(log.Fstr("piece %d completion unchanged", firstPieceIndex))
+			}
+			// Update the rest of the piece completions in the readahead window, without alerting to
+			// changes (since only the first piece, the one above, could have generated the read error
+			// we're currently handling).
+			if r.pieces.begin != firstPieceIndex {
+				panic(fmt.Sprint(r.pieces.begin, firstPieceIndex))
+			}
+			for index := r.pieces.begin + 1; index < r.pieces.end; index++ {
+				r.t.updatePieceCompletion(index)
+			}
+		}()
 	}
 }
 
 // Hodor
 func (r *reader) Close() error {
 	r.t.cl.lock()
-	defer r.t.cl.unlock()
 	r.t.deleteReader(r)
+	r.t.cl.unlock()
 	return nil
 }
 
@@ -258,28 +298,35 @@ func (r *reader) posChanged() {
 	r.t.readerPosChanged(from, to)
 }
 
-func (r *reader) Seek(off int64, whence int) (ret int64, err error) {
-	r.opMu.Lock()
-	defer r.opMu.Unlock()
-
-	r.mu.Lock()
-	defer r.mu.Unlock()
+func (r *reader) Seek(off int64, whence int) (newPos int64, err error) {
 	switch whence {
 	case io.SeekStart:
-		r.pos = off
+		newPos = off
+		r.mu.Lock()
 	case io.SeekCurrent:
-		r.pos += off
+		r.mu.Lock()
+		newPos = r.pos + off
 	case io.SeekEnd:
-		r.pos = r.length + off
+		newPos = r.length + off
+		r.mu.Lock()
 	default:
-		err = errors.New("bad whence")
+		return 0, errors.New("bad whence")
 	}
-	ret = r.pos
-
-	r.posChanged()
+	if newPos != r.pos {
+		r.reading = false
+		r.pos = newPos
+		r.contiguousReadStartPos = newPos
+		r.posChanged()
+	}
+	r.mu.Unlock()
 	return
 }
 
 func (r *reader) log(m log.Msg) {
-	r.t.logger.Log(m.Skip(1))
+	r.t.logger.LogLevel(log.Debug, m.Skip(1))
+}
+
+// Implementation inspired by https://news.ycombinator.com/item?id=27019613.
+func defaultReadaheadFunc(r ReadaheadContext) int64 {
+	return r.CurrentPos - r.ContiguousReadStartPos
 }