NSPR I/O functions and thread safety

Folks,

I'd like to know if there have been any efforts to make NSPR i/o
functions thread-safe? When for example a file operation is in
progress (sendfile?), if another thread comes along and deletes the
filedesc, what is the protection against it? Considering the fact that
NSPR supports multi-threading and file I/O, one would expect it to be
thread safe in this respect. Is this not a common requirement in
threaded applications?

Any help would be appreciated.

Thanks,
Anjuman