SR is a language for programming distributed systems ranging from operating systems to application programs. On the basis of our experience with the initial version, the language has evolved consider-ably. In this paper we describe the current version of SR and give an overview of its implementation. The main language constructs are still resources and operations. Resources encapsulate processes and variables that they share; operations provide the primary mechanism for process interaction. One way in which SR has changed is that both resources and processes are now created dynamically. Another change is that inheritance is supported. A third change is that the mechanisms for operation invocation-call and send-and operation implementation-proc and in-have been extended and integrated. Consequently, all of local and remote procedure call, rendezvous, dynamic process creation, asynchronous message passing, multicast, and semaphores are supported. We have found this flexibility to be very useful for distributed programming. Moreover, by basing SR on a small number of well-integrated concepts, the language has proved easy to learn and use, and it has a reasonably efficient implementation.

Heterogeneous Process Migration is a technique whereby an active process is moved from one machine to another. It must then continue normal execution and communication. The source and destination processors can have a different architecture, that is, different instruction sets and data formats. Because of this heterogeneity, the entire process memory image must be translated during the migration. "Tui" is a migration system that is able to translate the memory image of a program (written in ANSI-C) between four common architectures (m68000, SPARC, i486 and PowerPC). This requires detailed knowledge of all data types and variables used with the program. This is not always possible in non-type-safe (but popular) languages such as ANSI-C, Pascal and Fortran. The important features of the Tui algorithm are discussed in great detail. This includes the method by which a program's entire set of data values can be located, and eventually reconstructed on the target processor. Perfo...

Conventional compilers are designed for producing highly optimized code without paying much attention to compile time. The design goals of Java just-in-time compilers are different: produce fast code at the smallest possible compile time. In this article we present a very fast algorithm for translating JavaVM byte code to high quality machine code for RISC processors. This algorithm handles combines instructions, does copy elimination and coalescing and does register allocation. It comprises three passes: basic block determination, stack analysis and register preallocation, final register allocation and machine code generation. This algorithm replaces an older one in the CACAO JavaVM implementation reducing the compile time by a factor of seven and producing slightly faster machine code. The speedup comes mainly from following simplifications: fixed assignment of registers at basic block boundaries, simple register allocator, better exception handling, better memory management and fine...

This article describes the design and implementation of CACAO, a just in time compiler for Java. The CACAO system translates Java byte code on demand into native code for the ALPHA processor. During this translation process the stack oriented Java byte code is transformed into a register oriented intermediate code. Local variables and stack locations are replaced by pseudo registers eliminating the 32 bit restriction on address types. A fast register allocation algorithm is applied to map the pseudo registers to machine registers. During code generation, field offsets are computed for proper alignment on 64 bit architectures. Even though the CACAO system has to incur loading and compilation time, it executes Java programs up to 85 times faster than the JDK interpreter, up to 7 times faster than the kaffe JIT compiler. It is slightly slower than equivalent C programs compiled at the highest optimization level. 1 Introduction Java's [AG96] success as a programming language results from ...

machine designers have long recognized this dilemma. In 1972, Newey, Poole, and Waite [Newe79] observed that `Most problems will suggest a number of specialized operations which could possibly be implemented quite efficiently on certain hardware. The designer must balance the convenience and utility of these operations against the increased difficulty of implementing an abstract machine with a rich and varied instruction set.' Fortunately, applying all code improvements to the LIL removes efficiency considerations as HIL design issue. The abstract machine need only contain a set of features roughly equivalent to the intersection of the operations included in typical target machines. The result is a small, simple abstract machine. Such abstract machines are termed `intersection' machines. The analogy between union/intersection abstract machines and CISC/RISC architectures is obvious. void daxpy(n, da, dx, incx, dy, incy) int n, incx, incy; double da, dx[], dy[]; { if (n <= 0) return; i...

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machine modeling is a popular technique for developing portable compilers. A compiler can be quickly realized by translating the abstract machine operations to target machine operations. The problem with these compilers is that they trade execution efficiency for portability. Typically the code emitted by these compilers runs two to three times slower than the code generated by compilers that employ sophisticated code generators. This paper describes a C compiler that uses abstract machine modeling to achieve portability. The emitted target machine code is improved by a simple, classical rule-directed peephole optimizer. Our experiments with this compiler on four machines show that a small number of very general hand-written patterns (under 40) yields code that is comparable to the code from compilers that use more sophisticated code generators. As an added bonus, compilation time on some machines is reduced by 10 to 20 percent. KEY WORDS: Code generation Compilers Peephole optimizati...

As the price of CPU chips continues to fall rapidly, it will soon be economically feasible to build computer systems containing a large number of processors. The question of how this computing power should be organized, and what kind of operating system is appropriate then arises. Our research during the past decade has focused on these issues and led to the design of a distributed operating system, called Amoeba, that is intended for systems with large numbers of computers. In this paper we describe Amoeba, its philosophy, its design, its applications, and some experience with it. 1. INTRODUCTION The cost of CPU chips is expected to continue declining during the coming decade, leading to systems containing a large number of processors. Connecting all these processors using standard technology (e.g., a LAN) is easy. The hard part is designing and implementing software to manage and use all of this computing power in a convenient way. In this paper we describe a distributed operating s...

Languages with programmer-visible stacks (stack-based languages) are used widely, as intermediate languages (e.g., JavaVM, FCode), and as languages for human programmers (e.g., Forth, PostScript). However, the prevalent computer architecture is the register machine. This poses the problem of efficiently implementing stack-based languages on register machines. A straight-forward implementation of the stack consists of a memory area that contains the stack items, and a pointer to the top-of-stack item. The basic

day on the project, a second may have barely time to dabble in the project enough to keep current, while a third participant may be sent off on an urgent temporary assignment just before finishing a modification. It would be nice if each participant could be abstracted from the vicissitudes of the lives of the others. The system described here provides this abstraction by keeping the "files of the project" in a repository. It gives each participant his or her own copy of them and offers a number of commands to update the copy, to commit changes to the repository, etc. It is akin to some distributed file systems with optimistic concurrency control (see, e.g., Mullender and Tanenbaum[1] or Svobodova[2]), in so far as these are capable of implementing concurrency over a group of files. Its main novelties are its ease of use, its relative simplicity, and the length of the concurrency time span it supports (effectively forever). It is implemented as a simple set of command files ("shell scr