[Uri] URI thread safety documentation

[ohadschn]

The URI class is immutable, and glancing at the code it seems as though thread-safety is considered. However, the URI docs say "Any instance members are not guaranteed to be thread safe".

Is that really the case? If not, and the class is thread-safe, the docs should be updated.

[svick]

As far as I can tell from the discussion at https://github.com/dotnet/corefx/issues/13107, even though Uri does use locks, it is not thread-safe.

I believe the steps to take here are:

1. Fix https://github.com/dotnet/corefx/issues/13107, so Uri no longer locks on a string.
2. Check all code in Uri for thread-safety.
3. If Uri actually contains code that is not thread-safe, fix it.
4. Update the documentation, as you suggested.

[davidsh]

Also feel free to submit doc suggestions directly to the new docs location:
https://docs.microsoft.com/en-us/dotnet/api/system.uri?view=netcore-2.0

Clicking on the 'Edit' link will take you to the repo and allow you to submit PR's for suggestions.

[ohadschn]

@davidsh thank you for the reference, but as svick explained, these is engineering work involved before the docs can be updated.