Simplify parallelReader.Read() which also fixes previous implementation where it was returning before all the parallel reading go-routines had terminated which caused race conditions.
193 lines
4.9 KiB
Go
193 lines
4.9 KiB
Go
/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package cmd
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import (
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"context"
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"io"
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"sync"
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"github.com/minio/minio/cmd/logger"
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)
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// Reads in parallel from readers.
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type parallelReader struct {
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readers []io.ReaderAt
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dataBlocks int
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offset int64
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shardSize int64
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shardFileSize int64
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buf [][]byte
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}
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// newParallelReader returns parallelReader.
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func newParallelReader(readers []io.ReaderAt, e Erasure, offset, totalLength int64) *parallelReader {
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return ¶llelReader{
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readers,
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e.dataBlocks,
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(offset / e.blockSize) * e.ShardSize(),
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e.ShardSize(),
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e.ShardFileSize(totalLength),
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make([][]byte, len(readers)),
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}
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}
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// Returns if buf can be erasure decoded.
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func (p *parallelReader) canDecode(buf [][]byte) bool {
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bufCount := 0
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for _, b := range buf {
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if b != nil {
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bufCount++
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}
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}
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return bufCount >= p.dataBlocks
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}
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// Read reads from readers in parallel. Returns p.dataBlocks number of bufs.
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func (p *parallelReader) Read() ([][]byte, error) {
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newBuf := make([][]byte, len(p.readers))
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var newBufLK sync.RWMutex
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if p.offset+p.shardSize > p.shardFileSize {
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p.shardSize = p.shardFileSize - p.offset
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}
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readTriggerCh := make(chan bool, len(p.readers))
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for i := 0; i < p.dataBlocks; i++ {
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// Setup read triggers for p.dataBlocks number of reads so that it reads in parallel.
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readTriggerCh <- true
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}
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readerIndex := 0
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var wg sync.WaitGroup
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// if readTrigger is true, it implies next disk.ReadAt() should be tried
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// if readTrigger is false, it implies previous disk.ReadAt() was successful and there is no need
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// to try reading the next disk.
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for readTrigger := range readTriggerCh {
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newBufLK.RLock()
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canDecode := p.canDecode(newBuf)
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newBufLK.RUnlock()
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if canDecode {
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break
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}
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if readerIndex == len(p.readers) {
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break
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}
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if !readTrigger {
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continue
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}
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wg.Add(1)
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go func(i int) {
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defer wg.Done()
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disk := p.readers[i]
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if disk == nil {
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// Since disk is nil, trigger another read.
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readTriggerCh <- true
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return
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}
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if p.buf[i] == nil {
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// Reading first time on this disk, hence the buffer needs to be allocated.
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// Subsequent reads will re-use this buffer.
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p.buf[i] = make([]byte, p.shardSize)
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}
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// For the last shard, the shardsize might be less than previous shard sizes.
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// Hence the following statement ensures that the buffer size is reset to the right size.
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p.buf[i] = p.buf[i][:p.shardSize]
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_, err := disk.ReadAt(p.buf[i], p.offset)
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if err != nil {
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p.readers[i] = nil
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// Since ReadAt returned error, trigger another read.
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readTriggerCh <- true
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return
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}
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newBufLK.Lock()
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newBuf[i] = p.buf[i]
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newBufLK.Unlock()
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// Since ReadAt returned success, there is no need to trigger another read.
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readTriggerCh <- false
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}(readerIndex)
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readerIndex++
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}
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wg.Wait()
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if p.canDecode(newBuf) {
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p.offset += p.shardSize
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return newBuf, nil
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}
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return nil, errXLReadQuorum
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}
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// Decode reads from readers, reconstructs data if needed and writes the data to the writer.
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func (e Erasure) Decode(ctx context.Context, writer io.Writer, readers []io.ReaderAt, offset, length, totalLength int64) error {
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if offset < 0 || length < 0 {
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logger.LogIf(ctx, errInvalidArgument)
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return errInvalidArgument
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}
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if offset+length > totalLength {
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logger.LogIf(ctx, errInvalidArgument)
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return errInvalidArgument
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}
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if length == 0 {
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return nil
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}
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reader := newParallelReader(readers, e, offset, totalLength)
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startBlock := offset / e.blockSize
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endBlock := (offset + length) / e.blockSize
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var bytesWritten int64
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for block := startBlock; block <= endBlock; block++ {
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var blockOffset, blockLength int64
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switch {
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case startBlock == endBlock:
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blockOffset = offset % e.blockSize
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blockLength = length
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case block == startBlock:
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blockOffset = offset % e.blockSize
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blockLength = e.blockSize - blockOffset
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case block == endBlock:
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blockOffset = 0
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blockLength = (offset + length) % e.blockSize
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default:
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blockOffset = 0
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blockLength = e.blockSize
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}
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if blockLength == 0 {
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break
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}
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bufs, err := reader.Read()
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if err != nil {
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return err
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}
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if err = e.DecodeDataBlocks(bufs); err != nil {
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logger.LogIf(ctx, err)
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return err
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}
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n, err := writeDataBlocks(ctx, writer, bufs, e.dataBlocks, blockOffset, blockLength)
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if err != nil {
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return err
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}
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bytesWritten += n
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}
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if bytesWritten != length {
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logger.LogIf(ctx, errLessData)
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return errLessData
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}
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return nil
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}
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