You need R2020a or later to use parpool("threads")
Unfortunately, ticBytes() and tocBytes() do not work in parpool("threads") or backgroundPool so it is not possible to use those tools to compare the data transfer.
My understanding is that for ordinary numeric classes, that shared pointers are used for the different threads, but that if copy-on-write is needed that the newly allocated memory is on a per-thread memory pool (so that it can be easily released when the parfeval() finishes) . However, I have not yet been able to come up with a consistent internal description of how threads work that would lead to the same limitations as threads have -- the architectures I have come up with mentally would have fewer limitations than thread pools have in practice. Either that or the architectures I come up with might block all handle objects... I haven't figured out yet what Mathworks is doing that would allow some handle objects to work with thread-shared memory but would still require the same limitations that are seen in practice.
