cancel func()

	// ctx lives for the life of the transaction.
	ctx context.Context
}

// awaitDone blocks until the context in Tx is canceled and rolls back
// the transaction if it's not already done.
func (tx *Tx) awaitDone() {
	// Wait for either the transaction to be committed or rolled
	// back, or for the associated context to be closed.
	<-tx.ctx.Done()

			sink += b
		}
	}
	if r.closemuScanHold {
		t.Errorf("closemu held; should not be")
	}

	// There are 3 rows. We canceled after reading 2 so we expect either
	// 2 or 3 depending on how the awaitDone goroutine schedules.
	switch numRows {
	case 0, 1:
		t.Errorf("got %d rows; want 2+", numRows)
	case 2:
		if err := r.Err(); err != context.Canceled {
			t.Errorf("unexpected error: %v (%T)", err, err)