Rewrite of the AtomicReference

[marcpiechura]

Based on the gitter discussion I have rewritten the AtomicReference based on the DotNetty version.

• it is now restricted to reference types
• it uses Volatile Read/Write instead of Interlocked.MemoryBarrier for the Value property
• it has a new method to atomically get the current value and replace it with a new one

[marcpiechura]

This class has used the old version with a value type, therefore I have copied the old version into this class.

[rogeralsing]

Looks good to me.
cc Mr. Threading @JeffCyr

[JeffCyr]

Looks good for GetAndSet, but CompareAndSet doesn't look thread safe, it should use Interlocked.CompareExchange.

[JeffCyr]

I reviewed the other atomic utils and noted this:

• AtomicBoolean could be updated to also use Volatile.Read/Write
• AtomicCounter.Current should use Volatile.Read

[marcpiechura]

@JeffCyr The problem is that CompareExchange doesn't return a bool but rather the initial value. So would this be thread safe or is the equal operation not thread safe again?

var result = Interlocked.CompareExchange(ref atomicValue, newValue, expected);

return !Equals(result, newValue); 

Should I add the other classes to this PR as well?

[JeffCyr]

@Silv3rcircl3 It is thread-safe if you compare with the expected original value

var previous = Interlocked.CompareExchange(ref atomicValue, newValue, expected);
return Object.ReferenceEquals(previous, expected);

I think it's safer to compare the reference explicitly with ReferenceEquals. CompareExchange tests the reference here so it's useless to call a possibly overriden Equals method.

[marcpiechura]

@JeffCyr alright, thx for the info!

[Aaronontheweb]

We'll merge this in once @JeffCyr's comments are addressed

[marcpiechura]

@JeffCyr @Aaronontheweb updated.

[rogeralsing]

CoreAPISpec.ApproveCore

cc @Aaronontheweb how do we fix the above?

[marcpiechura]

It's working locally, don't know why it doesn't work with the CI server...
Maybe it's this https://github.com/akkadotnet/akka.net/pull/1615/files#diff-0b623d3c0315003b5801b3c3ce2d5a4dL3770 line, but locally it says I need to change it this way.
Could this be some sort of local language settings issue since I have a german windows + keyboard layout?

[rogeralsing]

@Silv3rcircl3 could be, what happens if you revert that line and push it here again?

[marcpiechura]

that's it... will also update my other PR's

[Horusiath]

👍

[Aaronontheweb]

Going to merge this one in