Adding Buffer Pooling to System.IO

[jonmill]

Starting to buffer all the things from #5598; adding Buffer Pooling to the BufferedStream, BinaryWriter, BinaryReader, and Stream classes.

Thanks to @ericstj for helping get the project.json and csproj files correct

@stephentoub @weshaggard

[KrzysztofCwalina]

Would it make sense to return the buffer before calling dispose on the stream? This would ensure the buffers are returned even if stream.Dispose throws.

[stephentoub]

Won't this end up returning these buffers twice if it's Dispose'd twice?

[KrzysztofCwalina]

Yeah, the code should guard against double return either by checking _isDisposed, or setting _buffer to null after the first clear. Also, this should be thread-safe.

[jonmill]

Fixed

[stephentoub]

Thanks for working on this.

[stephentoub]

@sokket, before doing further work on this, see the discussion here: #5954 (comment)

[stephentoub]

cc: @jkotas

[jonmill]

@stephentoub I didn't see a conclusion to that thread...should I back out this and the compression changes?

[stephentoub]

@sokket, thanks for doing this. Based on the discussion at the design meeting today, I'm closing this. In cases where these types are misused, we can't guarantee in these cases that we won't continue using the buffer even after it's been returned, e.g. BinaryReader passes its _buffer to the underlying Stream, which may be buggy and hold onto and use that byte[] well after it's been returned to the pool.