There are still a number of issues related to global values, which, if settable, need to have locking (so as not to get corrupted), or be stored in TLS.
Currently, there doesn’t seem to be any way (such as in C/C++) of indicating that a particular global should be thread specific, i.e. stored in TLS.
In particular, things like setting precision and rounding mode don’t work correctly with threads, also, conversions of numbers to strings (not just for I/O) which uses a fixed global buffer (DIGITS), is also broken.