We describe Charm++, an object oriented portable parallel programming language based on C++. Its design philosophy, implementation, sample applications and their performance on various parallel machines are described. Charm++ is an explicitly parallel language consisting of C++ with a few extensions. It provides a clear separation between sequential and parallel objects. The execution model of Charm++ is message driven, thus helping one write programs that are latencytolerant. The language supports multiple inheritance, dynamic binding, overloading, strong typing, and reuse for parallel objects. Charm++ provides specific modes for sharing information between parallel objects. Extensive dynamic load balancing strategies are provided. It is based on the Charm parallel programming system, and its runtime system implementation reuses most of the runtime system for Charm.

Inefficient implementations of global namespaces, message passing, and thread scheduling on stock multicomputers have prevented concurrent object-oriented programming (COOP) languages from gaining widespread acceptance. Recognizing that the architectures of stock multicomputers impose a hierarchy of costs for these operations, we have described a runtime system which provides different versions of each primitive, exposing performance distinctions for optimization. We confirm the advantages of a cost-hierarchy based runtime system organization by showing a variation of two orders of magnitude in version costs for a CM5 implementation. Frequency measurements based on COOP application programs demonstrate that a 39 % invocation cost reduction is feasible by simply selecting cheaper versions of runtime operations.

This article presents the design principles and efficient implementation techniques for ABCL/R3, an object-oriented concurrent reflective language. One of the most distinguished features of ABCL/R3 is compilation techniques using partial evaluation, which effectively remove interpretation from meta-level programs. The meta-level objects are designed so that they can be partially evaluated in an effective manner. Benchmark programs show that our compilation frameworks make object execution drastically faster than interpreter-based implementations, and achieves performance close to nonreflective compilers.

ICC++ is a new C++ concurrent dialect which allows sequential/parallel program versions to be maintained with single source, the construction of concurrent data abstractions, convenient expression of irregular and fine-grained concurrency, and supports high performance implementations. ICC++ provides annotations for potential concurrency, facilitating both sharing source with sequential programs and grain size tuning for efficient execution. ICC++ has a notion of object consistency which can be extended structurally and procedurally to implement larger data abstractions. Finally, ICC++ integrates arrays into the object system and hence the concurrency model. In short, ICC++ addresses concurrency and its relation to abstractions -- whether they are implemented by single objects, several objects, or object collections. The design of the language, its rationale, and current status are all described. Keywords concurrent object-oriented programming, concurrent languages, parallel...

The introduction of concurrency complicates the already difficult task of large-scale programming. Concurrent object-oriented languages provide a mechanism, encapsulation, for managing the increased complexity of large-scale concurrent programs, thereby reducing the difficulty of large scale concurrent programming. In particular, fine-grained object-oriented approaches provide modularity through encapsulation while exposing large degrees of concurrency. Though fine-grained concurrent object-oriented languages are attractive from a programming perspective, they have historically suffered from poor efficiency. The goal of the Concert project is to develop portable, efficient implementations of finegrained concurrent object-oriented languages. Our approach incorporates careful program analysis and information management at every stage from the compiler to the runtime system. In this document, we outline the basic elements of the Concert approach. In particular, we discuss progr...

Shared pools and stacks are two coordination structures with a history of applications ranging from simple producer/consumer buffers to job-schedulers and procedure stacks. This paper introduces elimination trees, a novel form of diffracting trees that offer pool and stack implementations with superior response (on average constant) under high loads, while guaranteeing logarithmic time "deterministic" termination under sparse request patterns. 1 A preliminary version of this paper appeared in the proceedings of the 7th Annual Symposium on Parallel Algorithms and Architectures (SPAA). Contact Author: E-mail:shanir@theory.lcs.mit.edu 1 Introduction As multiprocessing breaks away from its traditional number crunching role, we are likely to see a growing need for highly distributed and parallel coordination structures. A real-time application such as a system of sensors and actuators will require fast response under both sparse and intense activity levels (typical examples could be a ra...

We describe the design of a runtime system for a fine-grained concurrent object-oriented (actor) language and its performance. The runtime system provides considerable flexibility to users; specifically, it supports location transparency, actor creation and dynamic placement, and migration. The runtime system includes an efficient distributed name server, a latency hiding scheme for remote actor creation, and a compiler-controlled intra-node scheduling mechanism for local messages and dynamic load balancing. Our preliminary evaluation results suggest that the efficiency that is lost by the greater flexibility of actors can be restored by an efficient runtime system which provides an open interface that can be used by a compiler to allow optimizations. On several standard algorithms, the performance results for our system are comparable to efficient C implementations. Key Words: Concurrent Object-Oriented Programming, Actors, Location Transparency, Migration 1 Introduction We argue t...

The literature describes two high performance concurrent stack algorithms based on combining funnels and elimination trees. Unfortunately, the funnels are linearizable but blocking, and the elimination trees are non-blocking but not linearizable. Neither is used in practice since they perform well only at exceptionally high loads. The literature also describes a simple lock-free linearizable stack algorithm that works at low loads but does not scale as the load increases. The question of designing a stack algorithm that is non-blocking, linearizable, and scales well throughout the concurrency range, has thus remained open. This paper presents such a concurrent stack algorithm. It is based on the following simple observation: that a single elimination array used as a backoff scheme for a simple lock-free stack is lock-free, linearizable, and scalable. As our empirical results show, the resulting eliminationbackoff stack performs as well as the simple stack at low loads, and increasingly outperforms all other methods (lock-based and non-blocking) as concurrency increases. We believe its simplicity and scalability make it a viable practical alternative to existing constructions for implementing concurrent stacks.

It is difficult to map the execution model of multithread-ing languages (languages which support fine-grain dynamic thread creation) onto the single stack execution model of C. Consequently, previous work on efficient multithreading uses elaborate frame formats and allocation strategy, with com-pilers customized for them. This paper presents an alterna-tive cost-effective implementation strategy for multithread-ing languages which can maximally exploit current sequen-tial C compilers. We identify a set of primitives whereby ef-ficient dynamic thread creation and switch can be achieved and clarify implementation issues and solutions which work under the stack frame layout and calling conventions of cur-rent C compilers. The primitives are implemented as a C library and named StackThreads. In StackThreads, a thread creation is done just by a C procedure call, max-imizing thread creation performance. When a procedure suspends an execution, the context of the procedure, which is roughly a stack frame of the procedure, is saved into heap and resumed later. With StackThreads, the compiler writer can straightforwardly translate sequential constructs of the source language into corresponding C statements or expres-sions, while using StackThreads primitives as a blackbox mechanism which switches execution between C procedures.

A concurrent object-oriented extension to the programming language Scheme, called Schematic, is described. Schematic supports familiar constructs often used in typical parallel programs (future and higher-level macros such as plet and pbegin), which are actually defined atop a very small number of fundamental primitives. In this way, Schematic achieves both the convenience for typical concurrent programming and simplicity and flexibility of the language kernel. Schematic also supports concurrent objects which exhibit more natural and intuitive behavior than the "bare" (unprotected) shared memory, and permit intra-object concurrency. Schematic will be useful for intensive parallel applications on parallel machines or networks of workstations, concurrent graphical user interface programming, distributed programming over network, and even concurrent shell programming.