Safe and Efficient Hardware Specialization of Java Applications

Providing Java applications with access to low-level system resources, including fast network and I/O interfaces, requires functionality not provided by the Java Virtual Machine instruction set. Currently, Java applications obtain this functionality by executing code written in a lower-level language, such as C, through a native method interface. However, the overhead of this interface can be very high, and executing arbitrary native code raises serious protection and portability concerns. Jaguar [37] provides Java applications with efficient access to hardware resources through a bytecode specialization technique which transforms Java bytecode sequences to make use of inlined Jaguar bytecode which implements low-level functionality. Jaguar bytecode is portable and type-exact, making it both safer and more efficient than native methods. Jaguar requires that the target JVM or compiler recognizes Jaguar bytecode, which is a superset of the Java bytecode instruction set. We describe two implementations of Jaguar: one based on a static Java compiler, and the other which uses a standard JVM coupled with a Jaguar-enabled just-intime compiler. The JIT compiler applies code patches to the original Java bytecode, stored in the form of annotations in the Java class file. We demonstrate that Jaguar-specialized Java applications perform as well as C for a set of communication benchmarks, and that the code patching technique involves minimal compile-time