Function delay

cpp/src/arrow/dataset/file_test.cc:366–381

This kernel delays execution for some specific scalar values, which guarantees the writing phase sees out-of-order exec batches

// This kernel delays execution for some specific scalar values,
// which guarantees the writing phase sees out-of-order exec batches
Status delay(compute::KernelContext* ctx, const compute::ExecSpan& batch,
             compute::ExecResult* out) {
  const ArraySpan& input = batch[0].array;
  const auto* input_values = input.GetValues<uint32_t>(1);
  uint8_t* output_values = out->array_span()->buffers[1].data;

  // Boolean data is stored in 1 bit per value
  for (int64_t i = 0; i < input.length; ++i) {
    if (input_values[i] % 16 == 0) {
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }
    bit_util::SetBitTo(output_values, i, true);
  }

  return Status::OK();
}

// A fragment with start=0 will defer ScanBatchesAsync returning a batch generator
// This guarantees a dataset of multiple fragments could produce out-of-order batches