I'd rather put my eggs in the basket of the OSses fork than in Perl's implementation of threads. ;-) The advantage of forking over threading (beside a non-thread capable perl being faster) is that if problems like this are triggered by the drawing routine, all it can do is bring down the program that draws the graphs - you might miss a graph, but your collector will still run.

Personally, I would neither use fork(), nor threads. I'd write two programs, a data collector, and a graph drawer.

However, none of the above really helps with solving the glibc problem. Of that, I do not know the answer.