Location Independent Remote Execution in NEST

We consider a computing environment consisting of a network of autonomous, yet cooperating personal computer workstations and shared servers. Computing cycles in such an environment can be shared by creating a pool of compute servers in the network that may be used by the workstations to supplement their computing needs. Some processors may be permanently designated to be the compute servers. In addition, through an advertisement mechanism, any workstation may make itself temporarily available for a specific duration of time to be used as a compute server. In this paper, we present the design and implementation of a scheme for augmenting the UNIX® operating system with the location independent remote execution capability. This capability allows processes to be offloaded to the compute servers and preserves the execution environment of these processes as if they were still executing locally at the originating machine. Our model provides execution location independence of processes by preserving the process view of the file system, parent-child relationships, process groups, and process signaling across machine boundaries in a transparent way. We also present our scheme that allows processors to advertise themselves as available to some or all nodes in the network and withdraw as a compute server in a distributed manner. The scheme is robust in presence of node failures.     

Coach planning with opponent models for distributed execution

In multi-agent domains, the generation and coordinated execution of plans in the presence of adversaries is a significant challenge. In our research, a special “coach” agent works with a team of distributed agents. The coach has a global view of the world, but has no actions other than occasionally communicating with the team over a limited bandwidth channel. Our coach is given a set of predefined opponent models which predict future states of the world caused by the opponents’ actions. The coach observes the world state changes resulting from the execution of its team and opponents and selects the best matched opponent model based on its observations. The coach uses the recognized opponent model to predict the behavior of the opponent. Upon opportunities to communicate, the coach generates a plan for the team, using the predictions of the opponent model. The centralized coach generates a plan for distributed execution. We introduce (i) the probabilistic representation and recognition algorithm for the opponent models; (ii) a multi-agent plan representation, Multi-Agent Simple Temporal Networks; and (iii) a plan execution algorithm that allows the robust distributed execution in the presence of noisy perception and actions. The complete approach is implemented in a complex simulated robot soccer environment. We present the contributions as developed in this domain, carefully highlighting their generality along with a series of experiments validating the effectiveness of our coach approach.     

Defining and documenting execution viewpoints for a large and complex software-intensive system

An execution view is an important asset for developing large and complex systems. An execution view helps practitioners to describe, analyze, and communicate what a software system does at runtime and how it does it. In this paper, we present an approach to define and document viewpoints that guide the construction and use of execution views for an existing large and complex software-intensive system. This approach includes the elicitation of the organization's requirements for execution views, the initial definition and validation of a set of execution viewpoints, and the documentation of the execution viewpoints. The validation and application of the approach have helped us to produce mature viewpoints that are being used to support the construction and use of execution views of the Philips Healthcare MRI scanner, a representative large software-intensive system in the healthcare domain.     

A highly flexible multiprocessor solution for ray tracing

The ray tracing algorithm continues to attract much research and development to improve the quality of the images that are generated, and to reduce the time taken to produce them. By identifying the key requirements of a development system from the user's point of view, we describe a general-purpose multiprocessor solution for ray tracing which may be used to reduce execution time without restricting development of the ray tracing code. The solution is based upon a distributed memory multiprocessor system in which each processor addresses a small amount of memory relative to the size of the model database. Methods for exploiting the coherence of references to entries in the database are described which use a combination of dynamic and static caching techniques. This scheme allows databases of arbitrary size to be supported on multiprocessors with limited distributed memory.     

业务活动驱动系统体系结构执行研究

针对可执行体系结构研究中难以将业务体系结构的执行对应到系统体系结构的执行,并最终形成内在一致的执行体,提出了业务活动驱动系统体系结构执行的方法。该方法根据DoDAF中业务活动与系统功能多对多的关系,将业务活动用更详细的业务过程模型进行描述,并将过程模型中的行为单元对应到系统功能并触发该功能的执行。系统功能的执行将相应地触发一系列系统功能的执行,系统功能之间的系统数据交换将通过系统通信描述（SV-2）中的连接来实现,这样就建立起业务体系结构与系统体系结构之间的联系,并最终形成整个体系结构内在一致的执行体。该方法有效地解决了业务活动与系统功能之间多对多,无法形成内在一致的执行体问题,为体系结构的执行提供了一个明确、具体的可实施方案。     

Agent-based monitoring service for management of disruptive events in supply chains

Schedules of supply chains are generated with buffers to absorb the effect of disruptive events that could occur during their execution. Schedules can be systematically repaired through specific modifications within buffers by using appropriate decision models that consider the distributed nature of a supply chain. To this aim, information of disruptive events at occurrence or in advance allows decision models to make better decisions. To detect and predict disruptive events along a schedule execution, a service-oriented monitoring subsystem that uses a reference model for defining monitoring models was proposed. This subsystem offers services for collecting execution data of a schedule and environment data, and assessing them to detect/anticipate disruptive events. Because of the distributed nature and the complexity of these services functionalities, this paper presents an agent-based approach for their implementation. This technology allows dealing with supply chain monitoring by structuring monitoring subsystem functionalities as a set of autonomous entities. These entities are able to perform tailored plans created at execution time to concurrently monitor different schedules. A case study is described to try out the implemented prototype system.     

Peer-to-peer secure multi-party numerical computation facing malicious adversaries

We propose an efficient framework for enabling secure multi-party numerical computations in a Peer-to-Peer network. This problem arises in a range of applications such as collaborative filtering, distributed computation of trust and reputation, monitoring and other tasks, where the computing nodes are expected to preserve the privacy of their inputs while performing a joint computation of a certain function. Although there is a rich literature in the field of distributed systems security concerning secure multi-party computation, in practice it is hard to deploy those methods in very large scale Peer-to-Peer networks. In this work, we try to bridge the gap between theoretical algorithms in the security domain, and a practical Peer-to-Peer deployment. We consider two security models. The first is the semi-honest model where peers correctly follow the protocol, but try to reveal private information. We provide three possible schemes for secure multi-party numerical computation for this model and identify a single light-weight scheme which outperforms the others. Using extensive simulation results over real Internet topologies, we demonstrate that our scheme is scalable to very large networks, with up to millions of nodes. The second model we consider is the malicious peers model, where peers can behave arbitrarily, deliberately trying to affect the results of the computation as well as compromising the privacy of other peers. For this model we provide a fourth scheme to defend the execution of the computation against the malicious peers. The proposed scheme has a higher complexity relative to the semi-honest model. Overall, we provide the Peer-to-Peer network designer a set of tools to choose from, based on the desired level of security.     

An efficient checkpointing method for multicomputers with wormhole routing

Efficient checkpointing and resumption of multicomputer applications is essential if multicomputers are to support time-sharing and the automatic resumption of jobs after a system failure. We present a checkpointing scheme that is transparent, imposes overhead only during checkpoints, requires minimal message logging, and allows for quick resumption of execution from a checkpointed image. Furthermore, the checkpointing algorithm allows each processorp to continue running the application being checkpointed except during the time thatp is actively taking a local snapshot, and requires no global stop or freeze of the multicomputer. Since checkpointing multicomputer applications poses requirements different from those posed by checkpointing general distributed systems, existing distributed checkpointing schemes are inadequate for multicomputer checkpointing. Our checkpointing scheme makes use of special properties of wormhole routing networks to satisfy this new set of requirements.     

RTC: Language support for real-time concurrency

This paper presents a model and language constructs for expressing timing and concurrency requirements in distributed real-time programs. Our approach combines an abstract data type paradigm for the specification of shared resources and a distributed transaction-based paradigm for the specification of application processes. Resources provide abstract views of shared system entities, such as devices and data structures. Each resource has a state and defines a set ofactions that can be invoked by processes to examine or change its state. A resource also specifies scheduling constraints on the execution of its actions to ensure its consistency. Processes access resources by invoking actions and by expressing precedence, execution and timing constraints on action invocations. The implementation of our language constructs and the use of this system to control the simulation of a distributed robotics application is also described.This work is supported in part by the following grants: ARO DAAG-29-84-k-0061, ONR N000014-89-J-1131, and NSF CCR90-14621.     

Naming in the Distributed Operating System ZGL

In this paper,the naming scheme used in the heterogeneous distributed operating system ZGL is described and some of the representative techniques utilized in current distributed operating systems are examined.It is believed that the partitioning of the name space into manyn local name spaces and one global shared name space allows the ZGL system to satisfy each workstation‘s demand for local autonomy and still be able to facilitate transparent resource sharing.By the division of the system into clusters and the use of a combined centralized-distributed naming mechanism,the system is able to avoid both the bottleneck problem caused by a single centralized name server for the whole system and the performance degradation due to a full distributed scheme.     

Utopia: A load sharing facility for large,heterogeneous distributed computer systems

Load sharing in large, heterogeneous distributed systems allows users to access vast amounts of computing resources scattered around the system and may provide substantial performance improvements to applications. We discuss the design and implementation issues in Utopia, a load sharing facility specifically built for large and heterogeneous systems. The system has no restriction on the types of tasks that can be remotely executed, involves few application changes and no operating system change, supports a high degree of transparency for remote task execution, and incurs low overhead. The algorithms for managing resource load information and task placement take advantage of the clustering nature of large-scale distributed systems; centralized algorithms are used within host clusters, and directed graph algorithms are used among the clusters to make Utopia scalable to thousands of hosts. Task placements in Utopia exploit the heterogeneous hosts and consider varying resource demands of the tasks. A range of mechanisms for remote execution is available in Utopia that provides varying degrees of transparency and efficiency. A number of applications have been developed for Utopia, ranging from a load sharing command interpreter, to parallel and distributed applications, to a distributed batch facility. For example, an enhanced Unix command interpreter allows arbitrary commands and user jobs to be executed remotely, and a parallel make facility achieves speed-ups of 15 or more by processing a collection of tasks in parallel on a number of hosts.     

A middleware model supporting time-triggered message-triggered objects for standard Linux systems

The Time-triggered Message-triggered Object (TMO) programming and specification scheme came out of an effort to remove the limitations of conventional object structuring techniques in developing real-time (RT) distributed computing components and composing distributed computing applications out of such components and others. It is a natural and syntactically small but semantically powerful extension of the object oriented (OO) design and implementation techniques which allows the system designer to specify in natural and yet precise forms timing requirements imposed on data and function components of high-level distributed computing objects. TMO Support Middleware (TMOSM) was devised to be an efficient middleware architecture that can be easily adapted to many commercial-off-the-shelf (COTS) hardware + kernel operating system platforms to form efficient TMO execution engines. However, up until 2003, its adaptations were done for Microsoft Windows platforms only. As we have been developing and refining an adaptation of TMOSM to the Linux 2.6 operating system platform in recent years, TMOSM has been refined to possess further improved modularity and portability. This paper presents the refined TMOSM as well as the techniques developed for efficient adaptation of TMOSM to the Linux 2.6 platform.     

A framework for the application of metaheuristics to?tasks-to-processors assignation problems

The optimization of the execution time of a parallel algorithm can be achieved through the use of an analytical cost model function representing the running time. Typically the cost function includes a set of parameters that model the behavior of the system and the algorithm. In order to reach an optimal execution, some of these parameters must be fitted according to the input problem and to the target architecture. An optimization problem can be stated where the modeled execution time for the algorithm is used to estimate the parameters. Due to the large number of variable parameters in the model, analytical minimization techniques are discarded. Exhaustive search techniques can be used to solve the optimization problem, but when the number of parameters or the size of the computational system increases, the method is impracticable due to time restrictions. The use of approximation methods to guide the search is also an alternative. However, the dependence on the algorithm modeled and the bad quality of the solutions as a result of the presence of many local optima values in the objective functions are also drawbacks to these techniques. The problem becomes particularly difficult in complex systems hosting a large number of heterogeneous processors solving non-trivial scientific applications. The use of metaheuristics allows for the development of valid approaches to solve general problems with a large number of parameters. A well-known advantage of metaheuristic methods is the ability to obtain high-quality solutions at low running times while maintaining generality. We propose combining the parameterized analytical cost model function and metaheuristic minimization methods, which contributes to a novel real alternative to minimize the parallel execution time in complex systems. The success of the proposed approach is shown with two different algorithmic schemes on parallel heterogeneous systems. Furthermore, the development of a general framework allows us to easily develop and experiment with different metaheuristics to adjust them to particular problems.     

Combining Data and Computation Distribution Directives for Hybrid Parallel Programming : A Transformation System

This paper describes dSTEP, a directive-based programming model for hybrid shared and distributed memory machines. The originality of our work is the definition and an implementation of a unified high-level programming model addressing both data and computation distributions, providing a particularly fine control of the computation. The goal is to improve the programmer productivity while providing good performances in terms of execution time and memory usage. We define a generic compilation scheme for computation mapping and communication generation. We implement the solution in a source-to-source compiler together with a runtime library. We provide a series of optimizations to improve the performance of the generated code, with a special focus on reducing the communications time. We evaluate our solution on several scientific kernels as well as on the more challenging NAS BT benchmark, and compare our results with the hand written Fortran MPI and UPC implementations. The results show first that our solution allows to make explicit the non trivial parallel execution of the NAS BT benchmark using the dSTEP directives. Second, the results show that our generated MPI+OpenMP BT program runs with a 83.35 speedup over the original NAS OpenMP C benchmark on a hybrid cluster composed of 64 quadricores (256 cores). Overall, our solution dramatically reduces the programming effort while providing good time execution and memory usage performances. This programming model is suitable for a large variety of machines as multi-core and accelerator clusters.     

Security model oriented attestation on dynamically reconfigurable component-based systems

As more and more component-based systems (CBS) run in the open and dynamic Internet, it is very important to establish trust between clients and CBS in mutually distrusted domains. One of the key mechanisms to establish trust among different platforms in an open and dynamic environment is remote attestation, which allows a platform to vouch for its trust-related characteristics to a remote challenger. This paper proposes a novel attestation scheme for a dynamically reconfigurable CBS to reliably prove whether its execution satisfies the specified security model, by introducing a TPM-based attestation service to dynamically monitor the execution of the CBS. When only parts of the dynamic CBS are concerned, our scheme enables fine-grained attestation on the execution of an individual component or a sub-system in the dynamic CBS, such that it involves only minimal overhead for attesting the target parts of the CBS. With flexible attestation support, the proposed attestation service can attest a CBS at the granularity from an individual component to the whole CBS. As a case study, we have applied the proposed scheme on OSGi systems and implemented a prototype based on JVMTI for Felix. The evaluation results show that the proposed scheme is both effective and practical.     

适用于分布式DHR系统的可追溯直接匿名认证方案

作为拟态防御技术的基本实现模型, 动态异构冗余(Dynamic Heterogeneous Redundancy, DHR)系统在分布式场景下存在通信安全问题: 由于系统内缺乏对异构执行体的匿名保护措施以及诚实性度量方法, 异构执行体可能在未经察觉的情况下被攻击者入侵, 进而使得系统整体失效。将可信计算模块(Trusted Platform Module, TPM)引入分布式DHR系统可以缓解上述问题。然而, 现有TPM标准中使用的直接匿名认证(Direct Anonymous Attestation, DAA)方案会破坏分布式DHR系统的动态反馈机制, 因此无法直接应用于分布式DHR系统。为此,本文对DAA方案进行改进, 提出了一种适用于分布式DHR系统的可追溯直接匿名认证方案(Traceable Direct Anonymous Authentication Scheme, Tra-DAA)。本方案在维持系统内异构执行体对外匿名的同时, 为各异构执行体增加了内部追溯参数, 兼容了DHR系统的动态反馈性。此外, 我们引入了委托计算技术, 将TPM中的计算量降到了理论最低值。安全分析证明Tra-DAA在DL、DH、DBDH和LRSW假设下具备安全性, 即实现了匿名、证书不可伪造以及签名不可陷害。理论分析表明Tra-DAA相比多种代表性DAA方案在TPM运算量上具备显著优势。实验结果表明, Tra-DAA中新增的可追溯功能在整体耗时中仅占5%, 且Tra-DAA的整体效率相比TPM v2.0中的DAA方案有显著提升。具体来说, 在Join协议、伪名为空的Sign/Verifier协议, 以及伪名不为空的Sign/Verifier协议阶段, TPM的计算耗时分别缩短了33%、50%与70%。     

一种具有时间约束的分布式软件可靠性评估方法

在对分布式软件的可靠性进行评估时，通常采用以分布式程序为基础建立的相应模型，然而这些模型侧重于分布式软件的可靠性，很少反映具有时间约束特征的可靠性特性，以分布式软件的可靠性模型为基础，将精简和广度优先两种方法有机结合，对文件生成树中的数据文件传输时间进行评测，确定文件生成树的状态，从而提出一种具有实时特征的分布式软件可靠性评估方法。     

分布式工作流的动态管理

近些年来 ,分布式工作流管理系统设计已经成为计算机学者的研究热点。传统的工作流管理系统大多建立在客户机 /服务器模式上 ,采用集中式的方式。虽然易于实现、维护和管理 ,却存在着系统可扩展性、集成性差 ,产品可靠性、可用性不高 ,安全性能低的显著缺陷。采用分布式策略将工作流系统功能离散化或模块化 ,通过各个模块间的相互协调工作 ,实现预定功能 ,其优点在于能适应大吞吐量的要求、可扩展性高、可靠性强。然而 ,在现代企业管理中 ,由于流程模式改进、客户需求改变等原因迫使流程经常发生变迁。其必须在工作流结构中及时得到反映 ,这就使得动态管理技术在分布式工作流显得必不可少。将从建模、体系结构、运行环境、动态重组几个方面对分布式工作流的动态管理技术进行介绍和探讨。     

A modernized version of a 1D soil vegetation atmosphere transfer model for improving its future use in land surface interactions studies

SimSphere is a land biosphere model that provides a mathematical representation of vertical ‘views’ of the physical mechanisms controlling Earth's energy and mass transfers in the soil/vegetation/atmosphere continuum. Herein, we present recent advancements introduced to SimSphere code, aiming at making its use more integrated to the automation of processes within High Performance Computing (HPC) that allows using the model at large scale. In particular, a new interface to the model is presented, so-called “SimSphere-SOA” which forms a command line land biosphere tool, a Web Service interface and a parameters verification facade that offers a standardised environment for specification execution and result retrieval of a typical model simulation based on Service Oriented Architecture (SOA). SimSphere-SOA library can now execute various simulations in parallel. This allows exploitation of the tool in a simple and efficient way in comparison to the currently distributed approach. In SimSphere-SOA, an Application Programming Interface (API) is also provided to execute simulations that can be publicly consumed. Finally this API is exported as a Web Service for remotely executing simulations through web based tools. This way a simulation by the model can be executed efficiently and subsequently the model simulation outputs may be used in any kind of relevant analysis required.The use of these new functionalities offered by SimSphere-SOA is also demonstrated using a “real world” simulation configuration file. The inclusion of those new functions in SimSphere are of considerable importance in the light of the model's expanding use worldwide as an educational and research tool.