Implementing an applet system without fixing virtual‐machine designs

Abstract An applet is program code which is downloaded dynamically from a server on the World Wide Web and which can be executed while maintaining security on the client side. The majority of applet systems at present, as represented by the Java Applet, implement the applets using virtual machine code which is independent of computer architecture. This is advantageous in terms of installation and use in different machine environments. Because virtual machine code is associated with execution by an interpreter or conversion to native code, the design of the virtual machine code greatly impacts performance during execution. Normally, however, representation of virtual machine code is fixed for each applet system and cannot be altered. The authors focused on the independence of virtual machine code and implementing an applet execution environment which is independent of the design of virtual machine code by making the Just‐In‐Time (JIT) compiler which converts virtual machine code to native code mobile. In this approach, native code conversion modules which are appropriate for the virtual machine code being used in the applet description are downloaded dynamically. In addition, this applet execution environment provides monitoring functions during applet execution so that a native code applet generated from any virtual machine code can be executed safely. The applet execution monitoring mechanism allows for the programming of system control policies for users, and allows for flexible applet execution control for various levels of monitoring. In this paper, the authors describe an implementation using their newly designed virtual machine code representation in both the SPARC and Intel x86 architecture environments, as well as experiments using this implementation. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(2): 32–42, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/scj.10013