How to implement multi-threading bootstrapping using Bootstrap Evaluator ShallowCopy()?

[ThuryW]

I want to use goroutines to accelerate multiple bootstrapping, and I tried to use ShallowCopy() for Bootstrap Evaluator.

var wg sync.WaitGroup
ctO := make([]*rlwe.Ciphertext, 32)

for i := 0; i < 32; i++ {
wg.Add(1)
go func(index int) {
	defer wg.Done()
	ctO[index], _ = eval.ShallowCopy().Bootstrap(ciphertext1.CopyNew())
}(i)
}

I got the panic: level cannot be larger than max level

This issue does not only occur when using goroutines—even in a single-threaded scenario, the same error will appear when using ShallowCopy().

I wonder how to properly implement multi-threaded parallel bootstrapping?