)
// 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()
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
- // Reads have been initiated since the last seek. This is used to prevent readahead occuring
- // after a seek or with a new reader at the starting position.
- reading bool
- readahead int64
// Function to dynamically calculate readahead. If nil, readahead is static.
- readaheadFunc func() int64
+ 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
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.
func (r *reader) piecesUncached() (ret pieceRange) {
ra := r.readahead
if r.readaheadFunc != nil {
- ra = r.readaheadFunc()
+ 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
}
func (r *reader) ReadContext(ctx context.Context, b []byte) (n int, err error) {
- // 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()
if len(b) > 0 {
r.reading = true
// TODO: Rework reader piece priorities so we don't have to push updates in to the Client
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
}
}
func (r *reader) Seek(off int64, whence int) (newPos int64, err error) {
- r.opMu.Lock()
- defer r.opMu.Unlock()
- r.mu.Lock()
- defer r.mu.Unlock()
- newPos, err = func() (int64, error) {
- switch whence {
- case io.SeekStart:
- return off, err
- case io.SeekCurrent:
- return r.pos + off, nil
- case io.SeekEnd:
- return r.length + off, nil
- default:
- return r.pos, errors.New("bad whence")
- }
- }()
- if err != nil {
- return
+ switch whence {
+ case io.SeekStart:
+ newPos = off
+ r.mu.Lock()
+ case io.SeekCurrent:
+ r.mu.Lock()
+ newPos = r.pos + off
+ case io.SeekEnd:
+ newPos = r.length + off
+ r.mu.Lock()
+ default:
+ return 0, errors.New("bad whence")
}
- if newPos == r.pos {
- return
+ if newPos != r.pos {
+ r.reading = false
+ r.pos = newPos
+ r.contiguousReadStartPos = newPos
+ r.posChanged()
}
- 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 (r *reader) defaultReadaheadFunc() int64 {
- return r.pos - r.contiguousReadStartPos
+func defaultReadaheadFunc(r ReadaheadContext) int64 {
+ return r.CurrentPos - r.ContiguousReadStartPos
}