For example, in what concerns real time GCs, these are good books,

"Hard Realtime Garbage Collection in Modern Object Oriented Programming Languages."

https://www.amazon.com/Realtime-Collection-Oriented-Programm...

The author is one of the founders of Aicas real time JVM, https://www.aicas.com/wp/products-services/jamaicavm/

"Distributed, Embedded and Real-time Java Systems"

https://link.springer.com/book/10.1007/978-1-4419-8158-5

PTC is the other company alongside Aicas, that still sells real time Java systems, https://www.ptc.com/en/products/developer-tools/perc

IBM J9 has the evolution of the Metronome GC, https://www.researchgate.net/publication/220829995_The_Metro...

And it has extensions for value types, via packed object data, https://www.ibm.com/docs/en/sdk-java-technology/7.1?topic=ob...

Someone else already referred Azul, they also have extensions for value types, called object layouts, https://www.slideshare.net/AzulSystems/jvm-language-summit-o...

Then there are special flavours like microEJ or the Android Java snowflake.

Real Time Java has multiple ways to manage memory including arenas and deadlines for GC actions,

Aicas is the current steward company of the specification.

https://www.aicas.com/download/rtsj/rtsj_76.pdf

Books like "Hard Realtime Garbage Collection in Modern Object Oriented Programming Languages", from one of the Aicas' founders are quite interesting reads.

https://www.amazon.com/Realtime-Collection-Oriented-Programm...

Many discuss drop frames and jitter, while forgetting that a couple of ms more can result in someone's death in industrial automation or getting the wrong guys dead in weapon control systems.