J-Sim Core Features
J-Sim is an object-oriented library for discrete-time process-oriented simulation. Its main application area is queueing network simulation, however, the range of its use can be very wide – almost any system where object states change discretely can be modelled using J-Sim. J-Sim is a Simula-like simulation environment written in Java. For the programmer, it provides the same possibilities as the Simula language does. Plus much more.
The basic building blocks of every J-Sim simulation are processes, optionally queues, semaphores, message boxes, random-number generators, and other user-defines objects. Processes are active while other elements of the simulation are passive. The simulation is executed in a step-by-step manner. During a step, just one process is given an chance to run.
J-Sim is built up upon some very well known principles inherited from the Simula language, such as:
- life of processes, described as a sequence of actions;
- model time, shared by all processes within a simulation world;
- process state manipulation routines (hold(), passivate(), ...), controlling simulation progress;
- queue facilities HEAD and LINK, used for easy manipulation with queues and elements contained within them.
In addition to the standard features that a Simula user might expect, some extra features are provided:
- simulation of Dijkstra semaphores – processes may get blocked and unblocked on them;
- simulation of message passing – blocking and non-blocking send and receive operations; symmetric, asymetric, and indirect communication supported;
- independent random-number generators (exponential, Gaussian, boolean, and uniform distribution) that can be initialized by user-defined seed and therefore guarantee repeatability of experiments;
- console mode and two GUI modes (batch and interactive).
More information is available in the J-Sim Tutorial.
