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wal_reader.go
135 lines (108 loc) · 2.43 KB
/
wal_reader.go
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// Copyright 2023 StreamNative, 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 wal
import (
"sync"
"github.com/streamnative/oxia/proto"
)
func (t *wal) NewReader(after int64) (Reader, error) {
firstOffset := after + 1
if firstOffset < t.FirstOffset() {
return nil, ErrEntryNotFound
}
r := &forwardReader{
reader: reader{
wal: t,
nextOffset: firstOffset,
closed: false,
},
}
return r, nil
}
func (t *wal) NewReverseReader() (Reader, error) {
r := &reverseReader{reader{
wal: t,
nextOffset: t.LastOffset(),
closed: false,
}}
return r, nil
}
type reader struct {
// wal the log to iterate
wal *wal
nextOffset int64
closed bool
}
type forwardReader struct {
reader
sync.Mutex
}
type reverseReader struct {
reader
}
func (r *forwardReader) Close() error {
r.Lock()
defer r.Unlock()
r.wal.Lock()
defer r.wal.Unlock()
r.closed = true
return nil
}
func (r *reverseReader) Close() error {
r.closed = true
return nil
}
func (r *forwardReader) ReadNext() (*proto.LogEntry, error) {
timer := r.wal.readLatency.Timer()
defer timer.Done()
r.Lock()
defer r.Unlock()
if r.closed {
return nil, ErrReaderClosed
}
index := r.nextOffset
entry, err := r.wal.readAtIndex(index)
if err != nil {
return nil, err
}
r.nextOffset++
return entry, nil
}
func (r *forwardReader) HasNext() bool {
r.Lock()
defer r.Unlock()
if r.closed {
return false
}
return r.nextOffset <= r.wal.LastOffset()
}
func (r *reverseReader) ReadNext() (*proto.LogEntry, error) {
if r.closed {
return nil, ErrReaderClosed
}
entry, err := r.wal.readAtIndex(r.nextOffset)
if err != nil {
return nil, err
}
// If we read the first entry, this overflows to MaxUint64
r.nextOffset--
return entry, nil
}
func (r *reverseReader) HasNext() bool {
if r.closed {
return false
}
firstOffset := r.wal.FirstOffset()
return firstOffset != InvalidOffset && r.nextOffset != (firstOffset-1)
}