Improving System.IO.StreamReader buffer allocation

Hi,

last week I got bitten by System.IO.StreamReader - long story short, I found out that default bufferSize is set to 1024. Byte array is always allocated when StreamReader is instantiated. My StackOverflow post here.

I was immediately thinking about improving framework, but then realized it won’t be so easy. I will sum up my ideas below - didn’t want to start issue on GitHub before getting more feedback.

Also I think lowering buffer size seems to be enough. Is this even worth improving? Has this been discussed before?

1. Use ArrayPool

This could be the easiest way how to improve behavior of StreamReader. Renting array from pool and releasing it on Close. ArrayPool<T> is also part of common code, so I believe there won’t be problem with referencing it (… but I’m not sure).

However when buffer size is small, using ArrayPool<T> is not so effective (respective array pool behaves always the same no matter of how big chunk of memory you need, but it is slower than allocating small array directly).

2. Introduce another ctor overload

Allow user to supply StreamReader with own buffer array (probably rented from pool) or buffer factory - in both cases leaving responsibility on user.

but I can imagine this could lead to horrible things and more importantly, it would expose internal state of reader. Could this be considered as good design? I don’t think so.

3. Introducing new independent stream reader

Just introducing another stream reader class (which could use above mentioned ArrayPool<T>) - and I’m absolutely not sure about its name. This seems to be the most clean solution from code perspective, in other hand it creates another way how to solve one thing, making it less intuitive to user.

https://github.com/dotnet/corefx would be the right place to this issue.

1 Like

Ok! Will do - can we then remove this topic so it’s not on two places?

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