Java has significant overhead, that most/every object is allocated on heap, synchronized and has extra overhead of memory and performance to be GC controlled. Its very hard/not possible to tune this part.
You program differently for this niche in any language. The hot path (number crunching) thread doesn't share objects with gateway (IO) threads. Passing data between them is off heap, you avoid object creation after warm up. There is no synchronization, even volatile is something you avoid.
how exactly you are passing data? You can pass some primitives without allocating them on heap. You can use some tiny subset of Java+standard library to write high performance code, but why would you do this instead of using Rust or C++?
Strangely this is one of the areas where I want to use project panama so I might re-implement some of the ring buffers constructs.
You allocate off heap memory and dump data into it. With modern Java classes like Arena, MemoryLayout, and VarHandle it's honestly a lot like C structs.
> You allocate off heap memory and dump data into it. With modern Java classes like Arena, MemoryLayout, and VarHandle it's honestly a lot like C structs.
my opinion is that no, it is not, declaring and using C struct is 20x times more transparent, cost efficient and predictable. And that's we talking about C raw stucts, which has lots of additional ergonomics/safety/expression improvements in both c++ and rust on top of it.
