"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.
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()
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
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.
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
}
}
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 && len(b) > 0 {
panic("expected 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 || wanted == 0 {
+ case <-dontWait:
return
+ case <-readerCond:
}
- r.waitReadable(pos)
}
}
}
// 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
}
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
}
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
}