How to integrate shared variables in distributed simulation

Although users may want to employ shared variables when they program distributed simulation applications, almost none of the currently existing distributed simulation systems does offer this facility. In this paper, we systematically present new algorithms which provide consistent shared variables for distributed simulation applications. Basically, our approach combines known techniques to realize distributed shared memory with simulation algorithms. As there are essentially two classes of distributed simulation algorithms---conservative and optimistic---we study shared variable algorithms for both of them and propose five new algorithms. Initial performance measurements of a prototype implementation are described. Potential performance degradation by the usage of shared variables is expected to depend to a high degree on the access behavior of the simulation application. Having the abstraction of shared variables available provides the user with a simple concept to design distributed simulation applications in the presence of inherent global data.