Mobile agents are code-containing objects that may be transmitted between communicating participants in a distributed system. As opposed to systems that only allow the exchange of nonexecutable data, systems incorporating mobile agents can achieve significant gains in performance and functionality. A programming language for mobile agents must be able to express their construction, transmission, receipt, and subsequent execution. Its implementation must handle architectural heterogeneity between communicating machines and provide sufficient performance for applications based on agents. In addition to these essential properties, an agent language may support desirable properties such as high-level abstractions for code manipulation and the ability to access resources on remote execution sites. We designed and implemented an agent programming language that satisfies the essential properties and a number of desirable ones. A key feature of our language is the use of strong static typing ...

A technique for representing programs abstractly and independently of the eventual target architecture is presented that yields a file representation twice as compact as machine code for a CISC processor. It forms the basis of an implementation, in which the process of code generation is deferred until the time of loading. At that point, native code is created on_the_fly by a code_generating loader. The process of loading with dynamic code_generation is so fast that it requires little more time than the input of equivalent native code from a disk storage medium. This is predominantly due to the compactness of the abstract program representation, which allows to counterbalance the ad...

Software systems have been using “just-in-time ” compilation (JIT) techniques since the 1960s. Broadly, JIT compilation includes any translation performed dynamically, after a program has started execution. We examine the motivation behind JIT compilation and constraints imposed on JIT compilation systems, and present a classification scheme for

Traditional compiler optimizations are either dataindependent or optimize around common data values while retaining correct behavior for uncommon values. This paper examines value-specific data-dependent optimizations (VSO), where code is optimized at runtime around particular input values. Because VSO optimizes for the specific case, the resulting code is more efficient. However, since optimization is performed at runtime, the performance improvement must more than pay for the runtime compile costs. We describe two VSO implementation techniques and compare the performance of applications that have been implemented using both VSO and static code. The results demonstrate that VSO produces better code and often for reasonable input sizes. The machine-independent implementations showed speedups of up to 1.5 over static C code, and the machine-dependent versions showed speedups of up to 4.3 over static assembly code. 1 Introduction Traditional compiler optimizations are performed statical...

. A machine_independent abstract program representation is presented that is twice as compact as machine code for a CISC processor. It forms the basis of an implementation, in which the process of code generation is deferred until the time of loading. Separate compilation of program modules with type_safe interfaces, and dynamic loading (with code generation) on a per_module basis are both supported. To users of the implemented system, working with modules in the abstract representation is as convenient as working with native object_files, although it leads to several new capabilities. The combination of portability with practicality denotes a step toward a software component industry. 1. Introduction The rapid evolution of hardware technology is constantly influencing software development, for better as well as for worse. On the downside, faster hardware can conceal the complexity and cost of badly_designed programs; Reiser [Rei89] is not far off the mark in observing that s...

Lazy functional languages seem to be unsuitable for programming small computers because their implementations require so much memory for program code and graph. In this paper we argue that the program code can be made much smaller (withoutrunning much slower) by using the old idea of throw-away compilation. Our first results are promising --- programs using throw-away compilation typically run at 75% of the speed of those with ordinary compilation, but require only 25% of the code space. 1. Introduction Today computers lurk everywhere, heavily disguised as digital diaries, mobile telephones, video cameras and countless other electronic devices. However, it is most unlikely that any of these covert computers was programmed with a functional language. Traditionally, the execution speed of functional programs has been abysmal, and their memory requirements have been absurd. Yet two characteristics of the market lead us to believe that functional languages may one day be used to program c...

. The use of larger and more complex mobile agents in distributed applications has created a need for agent programming systems that deliver better performance. The implementation of Extended Facile, a mobile agent language, uses several strategies to boost performance. We review four main techniques: allowing agents to use different transmissible representations, optimistically transmitting machine code with agents, stripping agents of data and code that can be found at their recipients before transmitting them, and performing agent compilation lazily. Quantitative measurements show that these methods can boost absolute and relative performance. 1 Introduction Over the last two years interest in mobile agents has increased dramatically. Mobile agents, or more generally the ability to transmit code-containing objects between communicating participants, offer compelling advantages for constructing flexible and adaptable distributed systems. Uses of agents range from enriching client--s...