Span / Memory / ReadOnlySequence in C#

[giscus[bot]]

Span / Memory / ReadOnlySequence in C#

There are many different memory types used in modern C# programs. The more common ones are Span and Memory. Occasionally there is also ReadOnlySequence. What do these types do?

https://steven-giesel.com/blogPost/8bb02704-a113-40a1-9414-fe7b8cb3dda5

[ghadzhigeorgiev]

Thanks for pointing out the ReadOnlySequence. Somehow I've missed that one :)

[linkdotnet]

To be honest, I did not come across a useful scenario where I needed ReadOnlySequence. Did you @ghadzhigeorgiev ?

[ghadzhigeorgiev]

If I knew it existed, I could have used it in a project where data was in a file with a fixed size record structure. Could've used it to create a "filtered data reader" with results returned in a nice sequential access to them :)

[linkdotnet]

Ahh yeah that would be a really nice use case to "hide" the details and give the client code a nice an clean API. Love it (even though it doesn't help you now :D)

[gragra33]

I have looked at using ReadOnlySequenceSegment<T> and what is not mentioned, not that I can remember, is that all ReadOnlyMemory<T> segment must be the same size. If not, unsized segments are ascii(0) filled bytes to match sizes.

[linkdotnet]

I can not find any source referencing that fact - do you have any link?

[gragra33]

@linkdotnet Documentation on ReadOnlySequenceSegment<T> is very limited. The issue is that it is indirectly implied, not formally documented. How it is indirectly implied is via the ReadOnlySequenceSegment.RunningIndex Property. There is no tracking for each ReadOnlyMemory<T> segment size. it's assumed each is the same size.

I guess that you could track the size of each segment and manually dice and slice. This would kind of defeat the purpose of the ReadOnlySequenceSegment<T> class.

My usage, at the time, was for parsing streams using a PipeReader and buffering identified sections. I wanted to use ReadOnlySequenceSegment<T> however PipeReader.ReadAtLeastAsync(Int32, CancellationToken) Method returned variable chunch sizes, This caused the issue described.