mutual exclusion and barriers with libwww 3.0

I'm trying to do the following:

Create n threads which load n different pages
When each page is loaded, stores the data in one big structure
When all n pages have been loaded into the structure, start doing some analysis.

Obviously, I need a mutex around the structure, and some kind of
barrier before I do that analysis. Does libwww support this, or am I
going to be stuck doing this serially or playing with POSIX threads?