Geant4 is a toolkit for the simulation of the passage of particles through matter. Its areas of application include high energy, nuclear and accelerator physics, as well as studies in medical and space science. An effort is ongoing in order to provide a parallel version of it.
A prototype multi-threaded version, Geant4MT, parallelizes at the event level. The source code of the prototype is distributed separately from the production (sequential) Geant4, and is available []. Geant4MT was shown to be able to simulate a realistic HEP detector model, a version of the CMS geometry from 2008. . The threads share the geometry and EM-process cross sections as read only data.
The cost of the creation of extra workers represent only a small fraction of the total memory (the estimate is about an extra 20 MB per thread). One of the goals of this product is to achieve 100% reproducibility of the simulation.