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BufferedReader.go
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/
BufferedReader.go
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/*Package breader (Buffered File Reader), asynchronous parsing and pre-processing while
reading file. Safe cancellation is also supported.
Detail: https://github.com/shenwei356/breader
*/
package breader
import (
"errors"
"runtime"
"strings"
"sync"
"github.com/shenwei356/xopen"
"github.com/twotwotwo/sorts/sortutil"
)
// Chunk is a struct compossing with slice of data and error as status
type Chunk struct {
ID uint64 // useful for keeping the order of chunk in downstream process
Data []interface{}
Err error
}
// chunk is chunk of lines
type linesChunk struct {
ID uint64 // useful for keeping the order of chunk in downstream process
Data []string
}
// BufferedReader is BufferedReader
type BufferedReader struct {
reader *xopen.Reader
BufferSize int
ChunkSize int
ProcessFunc func(string) (interface{}, bool, error)
Ch chan Chunk
done chan struct{}
finished bool
cancelled bool
}
// NewDefaultBufferedReader creates BufferedReader with default parameter
func NewDefaultBufferedReader(file string) (*BufferedReader, error) {
reader, err := initBufferedReader(file, runtime.NumCPU(), 100, DefaultFunc)
if err != nil {
if err == xopen.ErrNoContent {
reader.Ch = make(chan Chunk, 100)
close(reader.Ch)
return reader, nil
}
return reader, err
}
reader.run()
return reader, nil
}
// NewBufferedReader is the constructor of BufferedReader with full parameters
func NewBufferedReader(file string, bufferSize int, chunkSize int, fn func(line string) (interface{}, bool, error)) (*BufferedReader, error) {
reader, err := initBufferedReader(file, bufferSize, chunkSize, fn)
if err != nil {
if err == xopen.ErrNoContent {
reader.Ch = make(chan Chunk, bufferSize)
close(reader.Ch)
return reader, nil
}
return reader, err
}
reader.run()
return reader, nil
}
// DefaultFunc just trim the new line symbol
var DefaultFunc = func(line string) (interface{}, bool, error) {
line = strings.TrimRight(line, "\r\n")
return line, true, nil
}
func initBufferedReader(file string, bufferSize int, chunkSize int, fn func(line string) (interface{}, bool, error)) (*BufferedReader, error) {
if bufferSize < 1 {
bufferSize = 1
}
if chunkSize < 1 {
chunkSize = 1
}
reader := new(BufferedReader)
fh, err := xopen.Ropen(file)
if err != nil {
return reader, err
}
reader.reader = fh
reader.BufferSize = bufferSize
reader.ChunkSize = chunkSize
reader.ProcessFunc = fn
reader.Ch = make(chan Chunk, bufferSize)
reader.done = make(chan struct{})
reader.finished = false
reader.cancelled = false
return reader, nil
}
// ErrorCanceled means that the reading process is canceled
var ErrorCanceled = errors.New("reading canceled")
func (reader *BufferedReader) run() {
ch2 := make(chan Chunk, reader.BufferSize)
// receive processed chunks and return them in order
go func() {
var id uint64
chunks := make(map[uint64]Chunk)
for chunk := range ch2 {
if chunk.Err != nil {
reader.Ch <- chunk
close(reader.Ch)
return
}
if chunk.ID == id {
reader.Ch <- chunk
id++
} else { // check bufferd result
for true {
if chunk1, ok := chunks[id]; ok {
reader.Ch <- chunk1
delete(chunks, chunk1.ID)
id++
} else {
break
}
}
chunks[chunk.ID] = chunk
}
}
if len(chunks) > 0 {
ids := make([]uint64, len(chunks))
i := 0
for id := range chunks {
ids[i] = id
i++
}
sortutil.Uint64s(ids)
for _, id := range ids {
chunk := chunks[id]
reader.Ch <- chunk
}
}
close(reader.Ch)
}()
// receive lines and process with ProcessFunc
ch := make(chan linesChunk, reader.BufferSize)
go func() {
defer close(ch2)
var wg sync.WaitGroup
tokens := make(chan int, reader.BufferSize)
errDetectedCh := make(chan int)
var once sync.Once
for chunk := range ch {
tokens <- 1
wg.Add(1)
go func(chunk linesChunk) {
defer func() {
wg.Done()
<-tokens
}()
var chunkData []interface{}
for _, line := range chunk.Data {
result, ok, err := reader.ProcessFunc(line)
if err != nil {
select {
case <-errDetectedCh:
default:
ch2 <- Chunk{chunk.ID, chunkData, err}
once.Do(func() { close(errDetectedCh) })
}
return
}
if ok {
chunkData = append(chunkData, result)
}
}
ch2 <- Chunk{chunk.ID, chunkData, nil}
}(chunk)
}
wg.Wait()
}()
// read lines
go func() {
var (
i int
id uint64
line string
err error
)
chunkData := make([]string, reader.ChunkSize)
for {
select {
case <-reader.done:
if !reader.finished {
reader.finished = true
reader.reader.Close()
close(ch)
return
}
default:
}
line, err = reader.reader.ReadString('\n')
if err != nil {
chunkData[i] = line
i++
ch <- linesChunk{id, chunkData[0:i]}
reader.finished = true
reader.reader.Close()
close(ch)
return
}
chunkData[i] = line
i++
if i == reader.ChunkSize {
ch <- linesChunk{id, chunkData[0:i]}
id++
chunkData = make([]string, reader.ChunkSize)
i = 0
}
}
}()
}
// Cancel method cancel the reading process
func (reader *BufferedReader) Cancel() {
if !reader.finished && !reader.cancelled {
close(reader.done)
reader.cancelled = true
}
}