An analytic model is proposed to assess the performance of optimistic software transactional memory (STM) systems with in-place memory updates for write operations. Based on an absorbing discrete-time Markov chain, closed-form analytic expressions are developed, which are quickly solved iteratively to determine key parameters of the STM system. The model covers complex implementation details such as read/write locking, data consistency checks and conflict management. It provides fundamental insight into the system behavior, when we vary input parameters like number and size of concurrent transactions or the number of the data objects. Numerical results are validated by comparison with a discrete-event simulation.

This paper presents an efficient and numerically reliable method for the transient analysis of deterministic and stochastic Petri nets. The transient behavior is described by state equations derived by the method of supplementary variables. Significant features of the proposed solution algorithm of fourth order are an automatic stepsize control and a two-stage relative error control. Furthermore, a formal way of dealing with discontinuities in the transient state equations is developed. This resolves the problems posed by initially enabled deterministic transitions and also improves the accuracy of numerical results. Experiments with a queueing system with failure and repair illustrate the efficiency (with respect to both CPU-time and memory space) and the numerical quality of the new algorithm.