batch.md

Batch processing

Concurrency

Every function and method in the package is safe for concurrent use, and a *qr.Code is immutable once returned, so you can encode and render from as many goroutines as you like. The encoder shares per-version tables across calls without locking.

Batch

Batch runs a slice of jobs on a worker pool and returns the results in job order. Each job has its own text, encode options, render options and output format:

results := qr.Batch(ctx, []qr.BatchJob{
	{Text: "https://example.com/1", Format: qr.FormatPNG},
	{Text: "https://example.com/2", Format: qr.FormatSVG,
		Encode: []qr.EncodeOption{qr.WithECC(qr.ECCHigh)},
		Render: []qr.RenderOption{qr.WithScale(4)}},
	{Text: "encode only"}, // FormatNone: Code is set, Data is nil
}, 0)

for i, r := range results {
	if r.Err != nil {
		log.Printf("job %d: %v", i, r.Err)
		continue
	}
	save(i, r.Data)
}

• The last argument is the number of workers; 0 or less means runtime.GOMAXPROCS(0).
• A failing job does not stop the others. When encoding succeeded but rendering failed, Code is still set.
• Canceling ctx skips jobs that have not started; they fail with ctx.Err().
• A panic in a job is reported as that job's error.

Throughput tips

• Prefer SVG for styled codes. It costs a fraction of an RGBA PNG.
• Reuse option slices. Build []qr.RenderOption once and pass it to every job.
• Keep the scale modest for PNG. Time grows with the number of pixels; WithScale(4) is plenty for screens.