_REENT_ONLY question

[Artem B. Bityuckiy]

Hello.

Please, can anybody explain me why _REENT_ONLY macro is needed? For 
what? Why some functions have on implementation and another have pair 
with _r postfix, e.g. setlocale() and _setlocale_r(), etc. Several 
functions have no such pair, e.g. ldiv(). And in all cases (that I've 
seen) usual functions call _r pair adding _REENT argument. For example 
'setlocale(category, locale)' just calls '_setlocale_r(p, category, 
locale), where p is 'struct _reent'. I can only guess that this is 
needed if external (not usual Newlib) "multiprocess support subsystem" 
is used...

Can anybody explain this and give me some examples when "_r" pairs are 
really useful/needed?

-- 
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.