You can paper over this with very large audio buffers (which makes the synth feel sluggish) or with crossed fingers (which work a surprising amount of the time).
It’s been a while since I was involved in computer audio, but is there a difficulty I’m not seeing with simply using ring buffers and doing memory allocations upfront so as to avoid GC altogether?
Even if you avoid GC, you need the memory used by the realtime code to be pinned to physical RAM to avoid paging.
The problem with GC is not (always) what it does, it's when it does it. You often do not have control over that, and if it kicks in the middle of otherwise realtime code ... not good.
It’s been a while since I was involved in computer audio, but is there a difficulty I’m not seeing with simply using ring buffers and doing memory allocations upfront so as to avoid GC altogether?