[plt-scheme] Using Scheme_Object * from another thread

L.S.,

Suppose, I would like to build up an array of arrays of Scheme_Object *
in an other OS thread then the mzscheme main OS thread, using 
scheme_malloc(), etc.
and scheme_make_utf8_string(), while the calling thread in mzscheme is
waiting on mzscheme_block_until().

Will this cause problems with mzscheme? (e.g. because schheme_malloc()/
scheme_make_utf8_string() is not OS thread safe).

Thanks in advance for answers,

Hans Oesterholt