84 The Execution Time Overhead of Entering and Exiting Scoped Memory in Real-Time Java Applications

Scoped memory management in RTSJ (Real-time Specification for Java) achieves a level of predictability not found in applications that use garbage collection techniques. However, using a scoped memory model is not an easy approach for developers to adopt. Satisfying reference rules between scopes for example constrains the design of the application's memory model. On the other hand, deciding on the appropriate number of scopes and which objects or threads should be allocated into those scopes are not straightforward tasks. The memory consumption and execution time overheads of the scopes need to be bounded. This paper presents a new empirical study of this memory model through a simulation of a railway control system executed in Sun's RTS2.2 virtual machine. The aim of this study is to measure the overhead of entering/exiting scoped memory regions. Results showed that entering/exiting active scopes has different execution time overhead than entering/exiting non-active ones.