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pool io.Copy buffers in ioCopier to reduce GC pressure #49

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pool io.Copy buffers in ioCopier to reduce GC pressure #49

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010dca5
Added a sync.Pool for 32KB copy buffers
migue Apr 7, 2026
22c71ee
Add test for pool buffer bypass via *os.File WriterTo
znull Apr 8, 2026
c5839cb
Fix pool buffer bypass caused by *os.File WriterTo
znull Apr 8, 2026
afe1947
Add test for ReaderFrom hidden by nopWriteCloser
znull Apr 8, 2026
6e7976a
Unwrap nopWriteCloser to expose ReaderFrom
znull Apr 8, 2026
60bd6c3
Fix lint errors in ioCopier tests
znull Apr 8, 2026
3f226f1
Merge pull request #50 from github/znull/sendfile
znull Apr 9, 2026
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15 changes: 14 additions & 1 deletion pipe/iocopier.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import (
"errors"
"io"
"os"
"sync"
)

// ioCopier is a stage that copies its stdin to a specified
Expand All @@ -15,6 +16,16 @@ type ioCopier struct {
err error
}

// copyBufPool reuses 32KB buffers across io.CopyBuffer calls, avoiding
// a fresh heap allocation per copy. This matters in high-throughput
// pipelines where many ioCopier stages run concurrently.
var copyBufPool = sync.Pool{
New: func() any {
b := make([]byte, 32*1024)
return &b
},
}

func newIOCopier(w io.WriteCloser) *ioCopier {
return &ioCopier{
w: w,
Expand All @@ -29,7 +40,9 @@ func (s *ioCopier) Name() string {
// This method always returns `nil, nil`.
func (s *ioCopier) Start(_ context.Context, _ Env, r io.ReadCloser) (io.ReadCloser, error) {
go func() {
_, err := io.Copy(s.w, r)
bp := copyBufPool.Get().(*[]byte)
_, err := io.CopyBuffer(s.w, r, *bp)
copyBufPool.Put(bp)
// We don't consider `ErrClosed` an error (FIXME: is this
// correct?):
if err != nil && !errors.Is(err, os.ErrClosed) {
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