Research Of Memory Management And Its Real-time Ability In JVM

Java has been more and more widely used in various fields depending on its advantages such as object-oriented language, platform-independent, security, high efficiency for development and so on. But due to its limitations, it can not be applied to real-time field. Since garbage collection will interrupt the running Java programs, which running time and garbage collection time are uncertain. When the frequency of allocation or release memory is high, the time of garbage collection may even be longer than the running time cost by the Java application. So these are the reason that Java program can not meet the demand in the real-time application fields.The mechanisms of memory management of Real-time Java Specification (RTSJ) not only ensure the advantage of security of Java, but also ensure the predictable of the operations to memory. Therefore, in real-time Java, it is necessary to improve and optimize the garbage collection technology. The codes that do not generate garbage will not request for garbage collection; The codes that do not have reference to heap memory can seize the garbage collection thread. In order to retain the benefits of garbage collection and avoid the impaction to the real-time performance by garbage collection, the RTSJ extend the Java memory management mechanism based on the two facts above. The RTSJ puts forward the concept of Memory Area. Allocate objects in these new memory areas will not cause garbage collection, and will cause unpredictable.According to the requirements of RTSJ, the RTSJ memory management mechanism of various basic elements is introduced in this paper, including the use of Display tree for memory inspection, the allocation mechanism of LTMemory and VTMemory, maintenance of Scope Stack. Based on an open-source Java Virtual Machine SableVM that can run on multiple operating systems, compatible with a variety of hardware platforms, on the basis of the latest theory at home and abroad, a scheme for improving its real-time performance is put forward and some experiments are done to verify it. The program is different from the existing domestic and international real-time Java Virtual Machine implementations. It not only is consistent with the requirements of RTSJ, but also ensures the portability of the Java programming requirements in memory management.