[.NET 6]A derived Random class still allocates possibly unnecessary memory #60549
Description
This is a follow up after fixing #57272.
Thanks to pull request #57530 a new Net5CompatDerivedImpl class has been introduced so it can be specialized for derived Random implementations.
Now I could test the latest release and unfortunately this implementation still initializes the _seedArray even if no base member will be called ever. Now that the possible scenarios have been separated the new Net5CompatDerivedImpl could initialize the _seedArray only on demand, when it is actually needed for the first time. I mentioned it in #57272 but the original reason of that issue was different. So now I created this one.
Of course, this would mean a minimal overhead but only when a derived instance calls some base implementation. In return the construction of the derived instance will be much faster and less memory consuming.
Update: API Proposal
To preserve the performance of the current behavior and fix the mentioned issue I propose the following new API
public class Random
{
// Determines the behavior of the base members for a derived Random class
// when using the new protected constructor.
protected enum BaseBehavior
{
// Base members use the original Random implementation.
// Instantiation generates a seed that allocates an array consuming 224 bytes
Compatible,
// Base members use the xoshiro** algorithm.
// Instantiation generates a seed consuming up to 32 bytes (on a 64 bit system)
// Can be useful if a derived class overrides some members and the rest should work
// the same way as the static Shared instance
Xoshiro,
// Base members rely on the protected Sample method
// Instantiation does not generate any seed in the base Random class
// Can be useful if a derived class overrides all members and does not call any base methods.
// Can be useful also when you want to override only the Sample method to provide
// a fully functional new Random implementation. This is useful also for tests that should
// produce prepared results as you don't need to override anything but the Sample method.
SampleBased
}
// protected constructor for derived classes
protected Random(BaseBehavior baseBehavior)
{
_impl = baseBehavior switch
{
BaseBehavior.Compatible => new Net5CompatDerivedImpl(this),
BaseBehavior.Xoshiro => new XoshiroImpl(),
BaseBehavior.SampleBased => new SampleBasedImpl(this), // TODO: new implementation
_ => throw new ArgumentOutOfRangeException(nameof(baseBehavior))
};
}
}