(Why) Is Java not available in a thread-based environment?

From my experience, using Java features (e.g. java.util.LinkedList) is smooth within MATLAB. However, these features are unavailable when called from a thread-based environment. A simplified example would be:

msgbase=javachk('jvm');
ph=parpool('Threads',2);
f=parfeval(ph,@jthreads,1);
[~,msgth]=f.fetchNext();
delete(ph);

function MSG=jthreads()
MSG=javachk('jvm');
end

Where msgbase would be empty, indicating Java is usable, but msgth would be 'This feature is not supported because:Java is not currently available.' I was not able to find a official statement on this issue, or a previous insightful discussion.

1. Is this expected behavior?
2. Can I modified settings or append some parameters to enable Java features inside a thread-based environment?
3. I'm not familar with C MEX funtions but I could learn. However, is C MEX functions supported inside a thread-based environment?

Thanks and regards!

Answer 1

[Damian Pietrus]

Currently, thread pools do not support all functions and features that process pools do. Stealing from our doc page here:

In general, functionality in Graphics, App Building, External Language Interfaces, Files and Folders, and Environment and Settings is not supported.

[Jan Kappen]

Interestingly, Python seems to be supported to some extend, see pass Python object as argument to function in "parfeval" - MATLAB Answers - MATLAB Central (mathworks.com)

Does this work with C/C++ and Java interfaces, too? Where exactly are the limitations?