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zstd: Use 1 less goroutine for stream decoding #588

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merged 1 commit into from May 12, 2022
Merged

zstd: Use 1 less goroutine for stream decoding #588

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93 changes: 41 additions & 52 deletions zstd/decoder.go
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Expand Up @@ -637,60 +637,18 @@ func (d *Decoder) startSyncDecoder(r io.Reader) error {

// Create Decoder:
// ASYNC:
// Spawn 4 go routines.
// 0: Read frames and decode blocks.
// 1: Decode block and literals. Receives hufftree and seqdecs, returns seqdecs and huff tree.
// 2: Wait for recentOffsets if needed. Decode sequences, send recentOffsets.
// 3: Wait for stream history, execute sequences, send stream history.
// Spawn 3 go routines.
// 0: Read frames and decode block literals.
// 1: Decode sequences.
// 2: Execute sequences, send to output.
func (d *Decoder) startStreamDecoder(ctx context.Context, r io.Reader, output chan decodeOutput) {
defer d.streamWg.Done()
br := readerWrapper{r: r}

var seqPrepare = make(chan *blockDec, d.o.concurrent)
var seqDecode = make(chan *blockDec, d.o.concurrent)
var seqExecute = make(chan *blockDec, d.o.concurrent)

// Async 1: Prepare blocks...
go func() {
var hist history
var hasErr bool
for block := range seqPrepare {
if hasErr {
if block != nil {
seqDecode <- block
}
continue
}
if block.async.newHist != nil {
if debugDecoder {
println("Async 1: new history")
}
hist.reset()
if block.async.newHist.dict != nil {
hist.setDict(block.async.newHist.dict)
}
}
if block.err != nil || block.Type != blockTypeCompressed {
hasErr = block.err != nil
seqDecode <- block
continue
}

remain, err := block.decodeLiterals(block.data, &hist)
block.err = err
hasErr = block.err != nil
if err == nil {
block.async.literals = hist.decoders.literals
block.async.seqData = remain
} else if debugDecoder {
println("decodeLiterals error:", err)
}
seqDecode <- block
}
close(seqDecode)
}()

// Async 2: Decode sequences...
// Async 1: Decode sequences...
go func() {
var hist history
var hasErr bool
Expand All @@ -704,7 +662,7 @@ func (d *Decoder) startStreamDecoder(ctx context.Context, r io.Reader, output ch
}
if block.async.newHist != nil {
if debugDecoder {
println("Async 2: new history, recent:", block.async.newHist.recentOffsets)
println("Async 1: new history, recent:", block.async.newHist.recentOffsets)
}
hist.decoders = block.async.newHist.decoders
hist.recentOffsets = block.async.newHist.recentOffsets
Expand Down Expand Up @@ -758,7 +716,7 @@ func (d *Decoder) startStreamDecoder(ctx context.Context, r io.Reader, output ch
}
if block.async.newHist != nil {
if debugDecoder {
println("Async 3: new history")
println("Async 2: new history")
}
hist.windowSize = block.async.newHist.windowSize
hist.allocFrameBuffer = block.async.newHist.allocFrameBuffer
Expand Down Expand Up @@ -845,6 +803,33 @@ func (d *Decoder) startStreamDecoder(ctx context.Context, r io.Reader, output ch

decodeStream:
for {
var hist history
var hasErr bool

decodeBlock := func(block *blockDec) {
if hasErr {
if block != nil {
seqDecode <- block
}
return
}
if block.err != nil || block.Type != blockTypeCompressed {
hasErr = block.err != nil
seqDecode <- block
return
}

remain, err := block.decodeLiterals(block.data, &hist)
block.err = err
hasErr = block.err != nil
if err == nil {
block.async.literals = hist.decoders.literals
block.async.seqData = remain
} else if debugDecoder {
println("decodeLiterals error:", err)
}
seqDecode <- block
}
frame := d.frame
if debugDecoder {
println("New frame...")
Expand All @@ -871,7 +856,7 @@ decodeStream:
case <-ctx.Done():
case dec := <-d.decoders:
dec.sendErr(err)
seqPrepare <- dec
decodeBlock(dec)
}
break decodeStream
}
Expand All @@ -891,6 +876,10 @@ decodeStream:
if debugDecoder {
println("Alloc History:", h.allocFrameBuffer)
}
hist.reset()
if h.dict != nil {
hist.setDict(h.dict)
}
dec.async.newHist = &h
dec.async.fcs = frame.FrameContentSize
historySent = true
Expand All @@ -917,7 +906,7 @@ decodeStream:
}
err = dec.err
last := dec.Last
seqPrepare <- dec
decodeBlock(dec)
if err != nil {
break decodeStream
}
Expand All @@ -926,7 +915,7 @@ decodeStream:
}
}
}
close(seqPrepare)
close(seqDecode)
wg.Wait()
d.frame.history.b = frameHistCache
}