Research On Agent Transparent Migration Based On Java

In mobile agent systems weak migration transfers code and data, while strong migration transfers code, data and execution state. All the operations of capturing and reestablishing the execution state are transparent to the programmer while using strong migration. So strong migration is also called transparent migration. Transparent migration play an important role in many application domains, e.g. computationally intensive application. At present the moible agent systems, which are constructed directly upon the code migration mechanism Java provides, e.g. Aglets, Mole, only support weak migration. They don't support transparent migration.This dissertation proposes a transparent agent migration mechanism based on continuation. The Java virtual machine is not modified, so this method is portable. This dissertation introduces continuation, which is a notion of functional programming language. Continuation contains the whole state at one point of a computational procedure, i.e. the execution state of a thread. After arriving at the target machine, the agent can reestablish the state by using continuation. The implementation of continuation depends on byte code transformation. This dissertation utilizes the byte code transformation interface and the annotation mechanism Java 5.0 provids, together with ASM(an open source byte code instrumentation tool) to instrument the byte code of agent. The thread state is stored in continuation, and the instructions to reestablish the state is innserted in the agent.This dissertation also provides a prototype implementation JMobile based on the above mechanism. JMobile contains three modules: continuation module, byte code instrumentation module and an agent migration module based on Java socket. The agent migration module implements the migration of agent by using the socket mechanism. The agent is instrumented by the byte code instrumentation module before loaded by the virtual machine. Then the agent is converted to a stream, which can migrate in the network with its exectution state. The observed perforamce measures are also reported, in terms of the sapce overhead and the run-time overhead by byte code instrumentation.