forked from dustin/go-wikiparse
/
multi_stream.go
171 lines (141 loc) · 3.29 KB
/
multi_stream.go
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package wikiparse
import (
"compress/bzip2"
"encoding/xml"
"io"
"log"
"os"
"sync"
)
type indexChunk struct {
offset int64
count int
}
type multiStreamParser struct {
siteInfo SiteInfo
workerch chan indexChunk
entries chan *Page
}
func multiStreamIndexWorker(r io.ReadCloser, p *multiStreamParser) {
defer close(p.workerch)
defer r.Close()
bz := bzip2.NewReader(r)
isr, err := NewIndexSummaryReader(bz)
if err != nil {
log.Fatalf("Error creating index summary: %v", err)
}
for {
offset, count, err := isr.Next()
p.workerch <- indexChunk{offset, count}
if err == io.EOF {
break
}
if err != nil {
log.Fatalf("Error reading stream: %v", err)
}
}
}
func multiStreamWorker(src IndexedParseSource, wg *sync.WaitGroup,
p *multiStreamParser) {
defer wg.Done()
r, err := src.OpenData()
if err != nil {
log.Fatalf("Error opening data: %v", err)
}
defer r.Close()
for idxChunk := range p.workerch {
_, err := r.Seek(idxChunk.offset, 0)
if err != nil {
log.Fatalf("Error seeking to specified offset: %v", err)
}
bz := bzip2.NewReader(r)
d := xml.NewDecoder(bz)
for i := 0; i < idxChunk.count && err != io.EOF; i++ {
newpage := &Page{}
err = d.Decode(newpage)
if err == nil {
p.entries <- newpage
}
}
}
}
// ReadSeekCloser is io.ReadSeeker + io.Closer.
type ReadSeekCloser interface {
io.ReadSeeker
io.Closer
}
// An IndexedParseSource provides access to a multistream xml dump and
// its index.
//
// This is typically downloaded as two files, but a seekable interface
// such as HTTP with range requests can also serve.
type IndexedParseSource interface {
OpenIndex() (io.ReadCloser, error)
OpenData() (ReadSeekCloser, error)
}
type filesSource struct {
idxfile, datafile string
}
func (f filesSource) OpenIndex() (io.ReadCloser, error) {
return os.Open(f.idxfile)
}
func (f filesSource) OpenData() (ReadSeekCloser, error) {
return os.Open(f.datafile)
}
// NewIndexedParserFromSrc creates a Parser that can parse multiple
// pages concurrently from a single source.
func NewIndexedParserFromSrc(src IndexedParseSource, numWorkers int) (Parser, error) {
r, err := src.OpenData()
if err != nil {
return nil, err
}
defer r.Close()
bz := bzip2.NewReader(r)
d := xml.NewDecoder(bz)
_, err = d.Token()
if err != nil {
return nil, err
}
si := SiteInfo{}
err = d.Decode(&si)
if err != nil {
return nil, err
}
rv := &multiStreamParser{
siteInfo: si,
workerch: make(chan indexChunk, 1000),
entries: make(chan *Page, 1000),
}
wg := sync.WaitGroup{}
wg.Add(numWorkers)
for i := 0; i < numWorkers; i++ {
go multiStreamWorker(src, &wg, rv)
}
ridx, err := src.OpenIndex()
if err != nil {
log.Fatalf("Error opening index: %v", err)
}
defer ridx.Close()
go multiStreamIndexWorker(ridx, rv)
go func() {
wg.Wait()
close(rv.entries)
}()
return rv, nil
}
// NewIndexedParser gets an indexed/parallel wikipedia dump parser
// from the given index and data files.
func NewIndexedParser(indexfn, datafn string, numWorkers int) (Parser, error) {
return NewIndexedParserFromSrc(filesSource{indexfn, datafn}, numWorkers)
}
func (p *multiStreamParser) Next() (rv *Page, err error) {
var ok bool
rv, ok = <-p.entries
if !ok {
return nil, io.EOF
}
return
}
func (p *multiStreamParser) SiteInfo() SiteInfo {
return p.siteInfo
}