  VORO++ is a software library written in C++ for computing the Voronoi
tessellation, a technique in computational geometry that is widely used for
analyzing systems of particles. VORO++ was released in 2009 and is based on
computing the Voronoi cell for each particle individually. Here, we take
advantage of modern computer hardware, and extend the original serial version
to allow for multithreaded computation of Voronoi cells via the OpenMP
application programming interface. We test the performance of the code, and
demonstrate that we can achieve parallel efficiencies greater than 95% in many
cases. The multithreaded extension follows standard OpenMP programming
paradigms, allowing it to be incorporated into other programs. We provide an
example of this using the VoroTop software library, performing a multithreaded
Voronoi cell topology analysis of up to 102.4 million particles.
