Special Issue on Java Technologies for Real-Time and Embedded Systems JTRES2013

The first paper [2] discusses software locking mechanisms that commonly protect shared resources for multi-threaded applications. This mechanism can, especially in chip-multiprocessor systems, result in a large synchronization overhead. For real-time systems in particular, this overhead increases the worstcase execution time and may void a task set's schedulability. This paper presents two hardware locking mechanisms to reduce the worst-case time required to acquire and release synchronization locks. These solutions are implemented for the chip-multiprocessor version of the Java Optimized Processor. The two hardware locking mechanisms are compared with a software locking solution as well as the original locking system of the processor. The hardware cost and performance are evaluated for all presented locking mechanisms. The performance of the better performing hardware locks is comparable to the original single global lock when contending for the same lock. When several non-contending locks are used, the hardware locks enable true concurrency for critical sections. Benchmarks show that using the hardware locks yields performance ranging from no worse than the original locks to more than twice their best performance. This improvement can allow a larger number of real-time tasks to be reliably scheduled on a multiprocessor real-time platform.