Implement AR transformation variant that uses Atomic classes without field updaters

[elizarov]

We need to implement a new transformation variant AR (in addition to existing FU and VH variants) that would transform classes using atomic objects to java.util.concurrent.Atomic* classes without using *FieldUpdater classes. The behavior of the (default) BOTH variant is to be decided later. See discussion in Kotlin/kotlinx.coroutines#490 on why this is needed and what should be the default.

[elizarov]

The decision is that we introduce a separate AR variant and leave BOTH working as it is now.

[elizarov]

(On hold for now, until we figure out how to reproduce original problem)

[xBlackCat]

Any updates for the two-years-old issue?

[qwwdfsad]

It's unlikely we are going to implement regular atomics transformation. The number of "bugged" devices in use is reducing each year and without them, such change has no benefits, only maintenance burden.

Additionally, we have to investigate the current state of Android multi-release JAR support

[JakeWharton]

The Android toolchain currently ignores MR jar classes as of sometime in the AGP 3.x series (~2-3 years ago).

[elizarov]

MR jars allow use to use BOTH strategy by default:

• FU variant by for Androind and JDK <= 8
• VH variant for JDK >= 9

However, I don't immeditely see how it helps with AR (Updater-less) transformation variant. Let's brainstorm. Is it somehow possible via ProGuard/R8 to ask for a class file replacement under specific circumstances (e.g for a specific range of min API versions). If that were possible, then we could implement AR variant, package these classes into some "normally hidden" place and ask Android toolchain to use them instead of FU variants when building DEX.