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reader.go
153 lines (143 loc) · 3.66 KB
/
reader.go
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package chunk
import (
"bytes"
"context"
"io"
"time"
"github.com/pachyderm/pachyderm/v2/src/internal/backoff"
"github.com/pachyderm/pachyderm/v2/src/internal/errors"
"github.com/pachyderm/pachyderm/v2/src/internal/miscutil"
"github.com/pachyderm/pachyderm/v2/src/internal/pacherr"
"github.com/pachyderm/pachyderm/v2/src/internal/pachhash"
"github.com/pachyderm/pachyderm/v2/src/internal/pctx"
"github.com/pachyderm/pachyderm/v2/src/internal/taskchain"
"golang.org/x/sync/semaphore"
)
// Reader reads data from chunk storage.
type Reader struct {
ctx context.Context
storage *Storage
client Client
dataRefs []*DataRef
offsetBytes int64
prefetchLimit int
}
func newReader(ctx context.Context, s *Storage, client Client, dataRefs []*DataRef, opts ...ReaderOption) *Reader {
r := &Reader{
ctx: ctx,
client: client,
storage: s,
dataRefs: dataRefs,
}
for _, opt := range opts {
opt(r)
}
for len(r.dataRefs) > 0 {
if r.dataRefs[0].SizeBytes > r.offsetBytes {
break
}
r.offsetBytes -= r.dataRefs[0].SizeBytes
r.dataRefs = r.dataRefs[1:]
}
return r
}
// Get writes the concatenation of the data referenced by the data references.
func (r *Reader) Get(w io.Writer) (retErr error) {
if len(r.dataRefs) == 0 {
return nil
}
if len(r.dataRefs) == 1 {
_, err := io.Copy(w, newDataReader(r.ctx, r.storage, r.client, r.dataRefs[0], r.offsetBytes))
return errors.EnsureStack(err)
}
ctx, cancel := pctx.WithCancel(r.ctx)
defer cancel()
taskChain := taskchain.New(ctx, semaphore.NewWeighted(int64(r.prefetchLimit)))
defer func() {
if retErr != nil {
cancel()
}
if err := taskChain.Wait(); retErr == nil {
retErr = err
}
}()
for i, dataRef := range r.dataRefs {
var offset int64
if i == 0 {
offset = r.offsetBytes
}
dr := newDataReader(r.ctx, r.storage, r.client, dataRef, offset)
if err := taskChain.CreateTask(func(ctx context.Context) (func() error, error) {
if err := dr.fetchData(); err != nil {
return nil, err
}
return func() error {
_, err := io.Copy(w, dr)
return errors.EnsureStack(err)
}, nil
}); err != nil {
return err
}
}
return nil
}
// DataReader is an abstraction that lazily reads data referenced by a data reference.
type DataReader struct {
ctx context.Context
client Client
memCache *memoryCache
deduper *miscutil.WorkDeduper[pachhash.Output]
dataRef *DataRef
offset int64
r io.Reader
}
func newDataReader(ctx context.Context, s *Storage, client Client, dataRef *DataRef, offset int64) *DataReader {
return &DataReader{
ctx: ctx,
client: client,
memCache: s.memCache,
deduper: s.deduper,
dataRef: dataRef,
offset: offset,
}
}
func (dr *DataReader) Read(data []byte) (int, error) {
if err := dr.fetchData(); err != nil {
return 0, err
}
n, err := dr.r.Read(data)
return n, errors.EnsureStack(err)
}
func (dr *DataReader) fetchData() error {
if dr.r != nil {
return nil
}
ref := dr.dataRef.Ref
b := backoff.NewExponentialBackOff()
b.InitialInterval = 1 * time.Millisecond
var data []byte
if err := backoff.RetryUntilCancel(dr.ctx, func() error {
chunkData, err := getFromCache(dr.memCache, ref)
if err != nil {
return err
}
data = chunkData[dr.dataRef.OffsetBytes+dr.offset : dr.dataRef.OffsetBytes+dr.dataRef.SizeBytes]
return nil
}, b, func(err error, _ time.Duration) error {
if !pacherr.IsNotExist(err) {
return err
}
return dr.deduper.Do(dr.ctx, ref.Key(), func() error {
data, err := Get(dr.ctx, dr.client, ref)
if err != nil {
return err
}
putInCache(dr.memCache, ref, data)
return nil
})
}); err != nil {
return err
}
dr.r = bytes.NewReader(data)
return nil
}