114 lines
2.4 KiB
Go
114 lines
2.4 KiB
Go
// Copyright 2023 PingCAP, Inc.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
package prefetch
|
|
|
|
import (
|
|
"bytes"
|
|
"io"
|
|
"sync"
|
|
)
|
|
|
|
// Reader is a reader that prefetches data from the underlying reader.
|
|
type Reader struct {
|
|
r io.ReadCloser
|
|
curBufReader *bytes.Reader
|
|
buf [2][]byte
|
|
bufIdx int
|
|
bufCh chan []byte
|
|
err error // after bufCh is closed
|
|
wg sync.WaitGroup
|
|
|
|
closed bool
|
|
closedCh chan struct{}
|
|
}
|
|
|
|
// NewReader creates a new Reader.
|
|
func NewReader(r io.ReadCloser, prefetchSize int) io.ReadCloser {
|
|
ret := &Reader{
|
|
r: r,
|
|
bufCh: make(chan []byte),
|
|
err: nil,
|
|
closedCh: make(chan struct{}),
|
|
}
|
|
ret.buf[0] = make([]byte, prefetchSize/2)
|
|
ret.buf[1] = make([]byte, prefetchSize/2)
|
|
ret.wg.Add(1)
|
|
go ret.run()
|
|
return ret
|
|
}
|
|
|
|
func (r *Reader) run() {
|
|
defer r.wg.Done()
|
|
for {
|
|
r.bufIdx = (r.bufIdx + 1) % 2
|
|
buf := r.buf[r.bufIdx]
|
|
n, err := r.r.Read(buf)
|
|
buf = buf[:n]
|
|
select {
|
|
case <-r.closedCh:
|
|
return
|
|
case r.bufCh <- buf:
|
|
}
|
|
if err != nil {
|
|
r.err = err
|
|
close(r.bufCh)
|
|
return
|
|
}
|
|
}
|
|
}
|
|
|
|
// Read implements io.Reader. Read should not be called concurrently with Close.
|
|
func (r *Reader) Read(data []byte) (int, error) {
|
|
total := 0
|
|
for {
|
|
if r.curBufReader == nil {
|
|
b, ok := <-r.bufCh
|
|
if !ok {
|
|
if total > 0 {
|
|
return total, nil
|
|
}
|
|
return 0, r.err
|
|
}
|
|
|
|
r.curBufReader = bytes.NewReader(b)
|
|
}
|
|
|
|
expected := len(data)
|
|
n, err := r.curBufReader.Read(data)
|
|
total += n
|
|
if n == expected {
|
|
return total, nil
|
|
}
|
|
|
|
data = data[n:]
|
|
if err == io.EOF || r.curBufReader.Len() == 0 {
|
|
r.curBufReader = nil
|
|
continue
|
|
}
|
|
}
|
|
}
|
|
|
|
// Close implements io.Closer. Close should not be called concurrently with Read.
|
|
func (r *Reader) Close() error {
|
|
if r.closed {
|
|
return nil
|
|
}
|
|
ret := r.r.Close()
|
|
close(r.closedCh)
|
|
r.wg.Wait()
|
|
r.closed = true
|
|
return ret
|
|
}
|