%% $Id: abstract.tex,v 1.5 2005/02/14 13:47:03 gokhale Exp $

\begin{abstract}

% Jeff: I agree with the first sentence, but I think society has a lot
% of big problems that need to be tackled and perhaps the first
% sentence could be reduced a little bit to focus on software
% development problems. Suggested change given below, but feel free to
% change it back if they feel strongly about it. 
% Andy - I rephrased the abstract

Some of the most challenging problems in high performance computing
are those associated with producing software for distributed, high
performance software (DHPS) systems in which distributed resources,
such as processors, sensors and networks coordinate to address high
performance computing needs of different domains. Supporting the
multiple simultaneous quality of service (QoS) and functional
requirements of DHPS systems is particularly vexing for DHPS system
developers and integrators, who must address these QoS and functional 
requirements without overcomplicating their solutions, 
degrading software quality, and exceeding project time 
and effort constraints. A key enabler in recent successes 
with small- to medium-scale DHPS systems has been middleware, which
provides reusable building blocks.  
However, as DHPS systems scale to form large ``composable systems 
of systems,'' the design space comprising available choices 
of reusable building blocks and services in middleware grows substantially. 
This limits the ability of the DHPS developers to make the 
right design choices, which adversely impacts validation and 
verification of performance of end systems, and hence project costs. 

To enable DHPS developers to make the right design choices, 
a systematic methodology to analyze the performance of DHPS 
systems at design time is necessary. Such a methodology may 
consist of models to analyze the performance of individual 
building blocks comprising the middleware and the composition of 
these building blocks. As a first step towards building this 
methodology, in this paper we present a model of the 
Reactor pattern, which provides the very important 
synchronous demultiplexing and dispatching capabilities in 
DHPS systems. The model is based on the 
Stochastic Reward Net (SRN) modeling paradigm. 
We illustrate how the model could be used relatively 
easily to obtain estimates of key performance metrics 
and for the sensitivity analysis of the Reactor pattern.

\end{abstract}
