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Large‐scale computing and data processing with cloud resources is gaining popularity. However, the usage of the cloud differs from traditional high‐performance computing (HPC) systems and both algorithms and codes have to be adjusted. This work is often time‐consuming and performance is not guaranteed. To address this problem we have developed the PCJ library (parallel computing in Java), a novel tool for scalable HPC and big data processing in Java. In this article, we present a performance evaluation of parallel applications implemented in Java using the PCJ library. The performance evaluation is based on the examples of highly scalable applications of different characteristics focusing on CPU, communication or I/O. They run on the traditional HPC system and Amazon web services Cloud as well as Linaro Developer Cloud. For the clouds, we have used Intel x86 and ARM processors for running Java codes without changing any line of the program code and without the need for time‐consuming recompilation. Presented applications have been parallelized using the partitioned global address space programming model and its realization in the PCJ library. Our results prove that the PCJ library, due to its performance and ability to create simple portable code, has great promise to be successful for the parallelization of various applications and run them on the cloud with a performance close to HPC systems. [ABSTRACT FROM AUTHOR]

Summary: Global load balancer libraries should be easy to use and allow users to easily obtain good performance for their applications on a variety of distributed systems. In this article, we introduce a new tuning mechanism to our Java implementation of the lifeline‐based global load balancer which automatically adjusts the task granularity to reach good performance based on some selected runtime metrics. We evaluate our system against four backtrack‐search problems on both a many‐core supercomputer environment and on a beowulf server, achieving ideal performance with our tuning mechanism on the supercomputer. We also identify the limits of our mechanism in handling situations with reduced imbalance. [ABSTRACT FROM AUTHOR]

Safety-Critical Java (SCJ) is a profile of the Real-Time Specification for Java that brings to the safety-critical industry the possibility of using Java. SCJ defines three compliance levels: Level 0, Level 1 and Level 2. The SCJ specification is clear on what constitutes a Level 2 application in terms of its use of the defined API but not the occasions on which it should be used. This paper broadly classifies the features that are only available at Level 2 into three groups: nested mission sequencers, managed threads and global scheduling across multiple processors. We explore the first two groups to elicit programming requirements that they support. We identify several areas where the SCJ specification needs modifications to support these requirements fully; these include the following: support for terminating managed threads, the ability to set a deadline on the transition between missions and augmentation of the mission sequencer concept to support composibility of timing constraints. We also propose simplifications to the termination protocol of missions and their mission sequencers. To illustrate the benefit of our changes, we present excerpts from a formal model of SCJ Level 2 written in Circus, a state-rich process algebra for refinement. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a framework that enables the development of Java applications that execute on CPUs, graphics processing units (GPUs) and clusters of CPUs/GPUs. Applications are specified in an OpenMP-like fashion, accessing data through a framework-provided data API. The framework enables the efficient execution of applications in CPU and/or GPU by relying on two key features: (i) parallelism exploitation patterns are specified by additional aspect modules; and (ii) data layout can be selected according to the target platform. This paper describes how the framework abstractions are mapped and how the framework intrinsically supports the development of applications with hybrid parallelism by composing aspect modules with a given base program. Performance results show that the framework provides a performance level similar to traditional approaches and enables better performance portability for a given base program. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Several software efforts have been produced over the past few years in various programming languages to help developers handle pseudorandom streams partitioning. Parallel and distributed stochastic simulations can obviously benefit from this kind of high-level tools. The latest release of the Java Development Kit (JDK 7) tries to tackle this problem by providing facilities to partition a pseudorandom stream across various threads thanks to the new class ThreadLocalRandom. Meanwhile, Java 7 offers a framework to split a problem in a divide and conquer way through the new class called ForkJoinPool. As any other Java thread pool, ForkJoin exploits threads as workers and manipulates the tasks that will be run on the workers. In ThreadLocalRandom, pseudorandom number generation is handled at a thread level. As a consequence, a scientific application taking advantage of a Java thread pool to parallelize its computation may suffer from a bad pseudorandom stream partitioning due to the behavior of ThreadLocalRandom. The present work introduces TaskLocalRandom, a task-level alternative to ThreadLocalRandom that solves this partitioning problem and assigns an independent pseudorandom stream to each task run in the thread pool. TaskLocalRandom is compatible with existing Java thread pools such as Executors or ForkJoin. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Multi-agent systems have been proven very effective for the modelling and simulation (M&S) of complex systems like those related to biology, engineering, social sciences and so forth. The intrinsic spatial character of many such systems leads to the definition of a situated agent. A situated agent owns spatial coordinates and acts and interacts with its peers in a hosting territory. In the context of parallel/distributed simulation of situated agent models, the territory represents a huge shared variable that requires careful handling. Frequent access by agents to territory information easily becomes a bottleneck degrading system performance and scalability. This paper proposes an original approach to modelling and distributed simulation of large-scale situated multi-agent systems. Time management is exploited for resolving conflicts and achieving data consistency while accessing the environment. The approach allows a simplification of the M&S tasks by making the modeller unaware of distribution concerns while ensuring the achievement of good scalability and performance during the distributed simulation. Practical aspects of the approach are demonstrated through some modelling examples based on Tileworld. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY The Java programming language was originally developed for embedded systems, but the resource requirements of previous and current Java implementations - especially memory consumption - tend to exclude them from being used on a significant class of resource constrained embedded platforms. The contribution of this paper is an architecture and implementation of a Java execution stack for resource constrained embedded platforms with a few kB of RAM and flash memory. The resource requirements of the presented architecture has been reduced significantly through all the layers of the architecture by integrating the following: (1) a lean virtual machine without any external dependencies on POSIX-like libraries or other OS functionalities; (2) a hardware abstraction layer, implemented almost entirely in Java through the use of hardware objects, first level interrupt handlers, and native variables; and (3) an implementation of the Safety-Critical Java profile Level 0 and 1 for hard real-time applications. All Java components of a given application are minimized through program specialization, and because (2) and (3) are written in Java, the program specialization has a significant impact on the resulting program size. An evaluation of the presented solution shows that the miniCDj benchmark gets reduced to a size where it can run on resource constrained platforms. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY Software transactional memory (STM) algorithms associate metadata with the memory locations accessed during a transaction's lifetime. This metadata may be stored in an external table by resorting to a mapping function that associates the address of a memory cell with the table entry containing the corresponding metadata (out-place or external strategy). Alternatively, the metadata may be stored adjacent to the associated memory cell by wrapping the cell and metadata together (in-place strategy). The implementation techniques to support these two approaches are very different and each STM framework is usually biased towards one of them, only allowing the efficient implementation of STM algorithms which suit one of the approaches and inhibiting a fair comparison with STM algorithms suiting the other. In this paper, we introduce a technique to implement in-place metadata that does not wrap memory cells, thus overcoming the bias and allowing STM algorithms to directly access the transactional metadata. The proposed technique is available as an extension to Deuce and enables the efficient implementation of a wide range of STM algorithms and their fair (unbiased) comparison in a common STM framework. We illustrate the benefits of our approach by analyzing its impact in two popular transactional memory algorithms with several transactional workloads, TL2 and multiversioning, each befitting out-place and in-place, respectively. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY Garbage collection is a well-known technique to increase program safety and developer productivity. Within the past few years, it has also become feasible for uniprocessor hard real-time systems. However, garbage collection for multi-processors does not yet meet the requirements of hard real-time systems. In this paper, we present a hard real-time garbage collector for a Java chip multi-processor that provides non-disruptive and analyzable behavior. For retrieving the references in local variables of threads, we propose a protocol that minimizes disruptions for high-priority tasks while still providing good bounds on the time until stack scanning finishes. Also, we developed a hardware unit that enables transparent, preemptible copying of objects, which eliminates the need to block tasks while copying objects. Evaluation of the hardware shows that the copy unit introduces only little overhead and does not limit the critical path. Analyses for different aspects of the system are presented, which indicate that comprehensive analysis of the presented system is indeed possible. Measurements resulted in release jitter for high-priority tasks of 362 μs or less on an embedded multi-processor with eight cores clocked at 100 MHz. This indicates that with the proposed garbage collector, high scheduling quality and garbage collection do not contradict each other on chip multi-processors. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This paper investigates face authentication based access control solutions for camera-equipped mobile devices. A new hierarchical correlation based face authentication (HCFA) scheme is proposed, which suits resource-constrained mobile devices such as mobile phones and personal digital assistants. The idea of HCFA is conducting a partial correlation output peak analysis (analyze the relationship between each cross-correlation output peak generated from selected sub-regions of a face), in conjunction with conventional direct cross-correlation methods. The experimental results on the public domain database demonstrate that the proposed scheme achieved better performance than that of the conventional direct correlation based schemes. Furthermore, HCFA was implemented on the Nokia S60 CLDC emulator using Java ME (previously J2ME) programming technology in order to test the applicability and implementability. The test results show that the proposed algorithm is implementable on mobile devices. It not only shortens processing time but also reduces resource demand significantly, compared with the direct correlation algorithms. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY Java still is a rather exotic language in the field of real-time and particularly embedded systems, eventhough it could provide productivity and especially safety and dependability benefits over the dominating language C. The reasons for the lack of acceptance of Java in the embedded world are the high resource consumption caused by the Java runtime environment and the lacking language features for low-level programming. KESO is a Java Virtual Machine (JVM) that was specifically designed for statically configured resource-constrained embedded systems. Rather than providing a fixed subset of the Java standard functionality, KESO uses the available ahead-of-time knowledge to generate a Java runtime that is specifically tailored towards the particular application. A key feature of KESO is its Multi-JVM architecture, which allows the isolated cohabitation of different applications on one hardware platform. Our evaluation uses two non-trivial real-time applications, a control application for a quadrotor helicopter and a collision detector, to compare the cost of an application using KESO to its C counterpart. Our results show that the resource consumption of applications developed on the base of KESO is comparable to C applications, and its mechanisms for communicating among isolated components are efficient and encourage the actual utilization of spatial isolation. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY Chip-multiprocessors offer increased processing power at a low cost. However, in order to use them for real-time systems, tasks have to be scheduled efficiently and predictably. It is well known that finding optimal schedules is a computationally hard problem. In this paper we present a solution that uses model checking to find a static schedule, if one exists at all, which gives an implementation of a table driven multiprocessor scheduler. Mutual exclusion to access shared resources is guaranteed by including access constraints in the schedule generation. To evaluate the proposed cyclic executive for multiprocessors, we have implemented it in the context of safety-critical Java on a Java processor. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We have designed a web-based software system for real-time interactive visualization of results taken from large-scale simulations of 3-D mantle convection and other large-scale modeling efforts. This approach allows for intense visualization sessions for a couple of hours as opposed to storing massive amounts of data in a storage system. Our data sets consist of 3-D data with over 10 million unknowns at each time-step to be used for volume rendering. Large-scale interactive visualization on a display wall holding 15 million pixels has already been accomplished. With the advent of the age of the mobile web, we have now extended this tactic to hand-held devices, such as the OQO, Nokia N800, netbooks, iPHONE, and Android OS phones. We are developing web-based software in Java to extend the ubiquitous use of this system across long distances. The software is aimed at creating an interactive and functional application capable of running on multiple browsers by taking advantage of two AJAX-enabled web frameworks: Echo2 (http://echo.nextapp.com/site/echo2) and Google Web Toolkit (http://code.google.com/webtoolkit/). Modular building of the system allows for components to be swapped out so that other forms of visualization can be accommodated, such as molecular dynamics in mineral physics or 2-D data sets from the regional convection models. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Implementing a concurrent programming language such as Java by means of a translator to an existing language is attractive as it provides portability over all platforms supported by the host language and reduces development time—as many low-level tasks can be delegated to the host compiler. The C and C++ programming languages are popular choices for many language implementations due to the availability of efficient compilers on a wide range of platforms. For garbage-collected languages, however, they are not a perfect match as no support is provided for accurately discovering pointers to heap-allocated data on thread stacks. We evaluate several previously published techniques and propose a new mechanism, lazy pointer stacks, for performing accurate garbage collection in such uncooperative environments. We implemented the new technique in the Ovm Java virtual machine with our own Java-to-C/C++ compiler using GCC as a back-end compiler. Our extensive experimental results confirm that lazy pointer stacks outperform existing approaches: we provide a speedup of 4.5% over Henderson's accurate collector with a 17% increase in code size. Accurate collection is essential in the context of real-time systems, we thus validate our approach with the implementation of a real-time concurrent garbage collection algorithm. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The semantics of the Java programming language require that the out-of-bounds array accesses be caught at runtime. In general, this requires dynamic checks at the time the array element is accessed. Some of these checks can be eliminated statically during just-in-time (JIT) compilation, but the most precise analyses are too expensive to run in JIT compilers. This paper presents a framework in which thorough static range analyses can be used safely during the less-performance-critical compilation of Java source into machine-independent mobile code. In this framework, the static analysis results are used to derive proofs that certain linear inequality constraints hold. These linear constraints and their proofs are then added to the mobile code as annotations. The annotation framework is designed so that proofs can be verified efficiently. This allows the JIT compiler to safely eliminate array bounds checks during compilation without an expensive runtime analysis. Experiments with a prototype system that can generate and verify these annotations demonstrate that this framework is more precise than prior work and that verification is efficient. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Distributed Java virtual machine (dJVM) systems enable concurrent Java applications to transparently run on clusters of commodity computers. This is achieved by supporting Java's shared-memory model over multiple JVMs distributed across the cluster's computer nodes. In this work, we describe and evaluate selective dynamic diffing and lazy home allocation, two new runtime techniques that enable dJVMs to efficiently support memory sharing across the cluster. Specifically, the two proposed techniques can contribute to reduce the overheads due to message traffic, extra memory space, and high latency of remote memory accesses that such dJVM systems require for implementing their memory-coherence protocol either in isolation or in combination. In order to evaluate the performance-related benefits of dynamic diffing and lazy home allocation, we implemented both techniques in Cooperative JVM (CoJVM), a basic dJVM system we developed in previous work. In subsequent work, we carried out performance comparisons between the basic CoJVM and modified CoJVM versions for five representative concurrent Java applications (matrix multiply, LU, Radix, fast Fourier transform, and SOR) using our proposed techniques. Our experimental results showed that dynamic diffing and lazy home allocation significantly reduced memory sharing overheads. The reduction resulted in considerable gains in CoJVM system's performance, ranging from 9% up to 20%, in four out of the five applications, with resulting speedups varying from 6.5 up to 8.1 for an 8-node cluster of computers. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Increasing synchronization performance is one of the most important factors for improving Java performance. We present the concept of quasi-immutable objects and its application to implement fast synchronization primitives. Quasi-immutable objects are usually used for read accesses, but they are rarely used for write accesses. Using these characteristics, we describe the optimization for a synchronized read sequence of quasi-immutable objects. Our described method dynamically detects objects that are not written from critical sections of other threads, and applies the fast read sequence. The optimized read sequence enables the simultaneous execution of critical sections by multiple threads and reduces synchronization overhead. We implemented the described optimization on HotSpot Java VM. The experimental evaluations indicated that the optimization improved the performance of a micro-benchmark up to a factor of 16 and SPEC benchmarks up to 31%. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Although OpenMP is a widely agreed-upon standard for the C/C++ and Fortran programming languages for the semi-automatic parallelization of programs for shared memory machines, not much has been done on the binding of OpenMP to Java that targets clusters with distributed memory. This paper presents three major contributions: (1) JaMP is an adaptation of the OpenMP standard to Java that implements a large subset of the OpenMP specification with an expressiveness comparable to that of OpenMP; (2) we suggest a set of extensions that allow a better integration of OpenMP into the Java language; (3) we present our prototype implementation of JaMP in the research compiler Jackal, a software-based distributed shared memory implementation for Java. We evaluate the performance of JaMP with a set of micro-benchmarks and with OpenMP versions of the parallel Java Grande Forum (JGF) benchmarks. The micro-benchmarks show that OpenMP for Java can be implemented without much overhead. The JGF benchmarks achieve a good speed-up of 5–8 on eight nodes. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Access to the computational Grid is restricted to the laptop and desktop environment since Grid client development has been concentrated in this area. This paper presents the design and implementation of a new, lightweight computational Grid client that provides the same level of functionality and security as its desktop counterparts whilst conforming to the limitations and restrictions of a Personal Digital Assistant environment. A solution has been achieved by taking an architectural perspective of the problem and choosing a tiered, asymmetrical Grid middleware providing an asynchronous messaging model with uniform interface to all resources. The client opens up a new area of Grid computing access: secure and flexible job submission and monitoring to dependable, persistent, powerful and consistent computing services provided by a computational Grid has been freed from static environments into the mobile domain. This has been done without the modification of the underlying Grid middleware and using standards-based protocols and components: J2ME, X.509 certificates, Secure Socket Layer connections and IEEE 802.11b wireless networking. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Java programming language supports concurrency. Concurrent programs are harder to verify than their sequential counterparts due to their inherent non-determinism and a number of specific concurrency problems, such as interference and deadlock. In previous work, we have developed the ConAn testing tool for the testing of concurrent Java components. ConAn has been found to be effective at testing a large number of components, but there are certain classes of failures that are hard to detect using ConAn. Although a variety of other verification tools and techniques have been proposed for the verification of concurrent software, they each have their strengths and weaknesses. In this paper, we propose a method for verifying concurrent Java components that includes ConAn and complements it with other static and dynamic verification tools and techniques. The proposal is based on an analysis of common concurrency problems and concurrency failures in Java components. As a starting point for determining the concurrency failures in Java components, a Petri-net model of Java concurrency is used. By systematically analysing the model, we come up with a complete classification of concurrency failures. The classification and analysis are then used to determine suitable tools and techniques for detecting each of the failures. Finally, we propose to combine these tools and techniques into a method for verifying concurrent Java components. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The PGPGrid project aims to parallelize the process of extracting range data from an experimental 3D scanner using the Grid as a vehicle for accessing necessary resources. The application is potentially highly parallel but has some unusual features such as rapid spawning of processes in real time and a dynamic inter-process network topology. These characteristics are such as to require enhancement of the usual task migration capabilities of the Globus toolkit. The present paper initially discusses attempts to estimate the real parallelizability of the scanner application. It then describes a new Java application programming interface, based on Milner's $\pi$-calculus, which could be used to extend Globus in a manner capable of supporting systems with this kind of dynamic parallel structure. The location of processing resources for the $\pi$-calculus is done using a Web-services-based resource locator. The article also describes the pipeline of processing from initial stereo photogrametry to the final production of animation models. A key step in this is the conformation of animators models to the data obtained by the real-time scanner. Algorithmic innovations in this process are described. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper proposes two approaches to managing concurrency in Java using a guarded region abstraction. Both approaches use revocation of such regions—the ability to undo their effects automatically and transparently. These new techniques alleviate many of the constraints that inhibit construction of transparently scalable and robust concurrent applications. The first solution, revocable monitors, augments existing mutual exclusion monitors with the ability to dynamically resolve priority inversion and deadlock, by reverting program execution to a consistent state when such situations are detected, while preserving Java semantics. The second technique, transactional monitors, extends the functionality of revocable monitors by implementing guarded regions as lightweight transactions that can be executed concurrently (or in parallel on multiprocessor platforms). The presentation includes discussion of design and implementation issues for both schemes, as well as a detailed performance study to compare their behavior with the traditional, state-of-the-art implementation of Java monitors based on mutual exclusion. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In parallel and distributed applications, it is very likely that object-oriented languages, such as Java and Ruby, and large-scale semistructured data written in XML will be employed. However, because of their inherent dynamic memory management, parallel and distributed applications must sometimes suspend the execution of all tasks running on the processors. This adversely affects their execution on the parallel and distributed platform. In this paper, we propose a new task scheduling method called CP/MM (Critical Path/Memory Management) which can efficiently schedule tasks for applications requiring memory management. The underlying concept is to consider the cost due to memory management when the task scheduling system allocates ready (executable) coarse-grain tasks, or macro-tasks, to processors. We have developed three task scheduling modules, including CP/MM, for a task scheduling system which is implemented on a Java RMI (Remote Method Invocation) communication infrastructure. Our experimental results show that CP/MM can successfully prevent high-priority macro-tasks from being affected by the garbage collection arising from memory management, so that CP/MM can efficiently schedule distributed programs whose critical paths are relatively long. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Leveraged by the success of applications aiming at the ‘free’ sharing of data in the Internet, the paradigm of peer-to-peer (P2P) computing has had substantial consideration devoted to it recently. This paper presents a high-level abstraction for remote object interaction in a P2P environment, called borrow/lend (BL). We present the principles underlying our BL abstraction, and illustrate how this abstraction can be used to program P2P applications in Java. We contrast our abstraction with established abstractions for distributed programming such as the remote method invocation or the tuple space, illustrating how the BL abstraction, obviously influenced by such previous abstractions, unifies flavors of these, but also how it captures the constraints specific to P2P environments. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper addresses functionality and implementation of a HPJava version of the Adlib collective communication library for data parallel programming. We begin by illustrating typical use of the library, through an example multigrid application. Then we describe implementation issues for the high-level library. At a software engineering level, we illustrate how the primitives of the HPJava language assist in writing library methods whose implementation can be largely independent of the distribution format of the argument arrays. We also describe a low-level API called mpjdev, which handles basic communication underlying the Adlib implementation. Finally we present some benchmark results, and some conclusions. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Plasma simulation is an important example of a high-performance computing application where computer science issues are of great relevance. In a plasma, each particle, electron or ion, interacts with the external fields and with other particles in ways that can be readily and effectively emulated using object-oriented programming. However, the great cost of plasma simulations has traditionally discouraged object-oriented implementations due to their perceived inferior performance compared with classic procedural FORTRAN or C. In the present paper, we revisit this issue. We have developed a Java particle-in-cell code for plasma simulation, called Parsek. The paper considers different choices for the object orientation and tests their performance. We find that coarse-grained object orientation is faster and practically immune from any degradation compared with a standard procedural implementation (with static classes). The loss in performance for a fine-grained object orientation is a factor of about 50%, which can be almost completely eliminated using advanced Java compilation techniques. The Java code Parsek also provides an interesting realistic application of high-performance computing to compare the performance of Java with FORTRAN. We have conducted a series of tests considering various Java implementations and various FORTRAN implementations. We have also considered different computer architectures and different Java Virtual Machines and FORTRAN compilers. The conclusion is that with Parsek, object-oriented Java can reach CPU speed performances more or less comparable with procedural FORTRAN. This conclusion is remarkable and it is in agreement with the most recent benchmarks, but is at variance with widely held misconceptions about the alleged slowness of Java. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recently there has been an increasing interest in developing parallel programming capabilities in Java to harness the vast resources available in clusters, grids and heterogeneous networked systems. In this paper, we introduce a Java object-passing interface (JOPI) library. JOPI provides Java programmers with the necessary functionality to write object-passing parallel programs in distributed heterogeneous systems. JOPI provides a Message Passing Interface (MPI)-like interface that can be used to exchange objects among processes. In addition to the well-known benefits of the object-oriented development model, using objects to exchange information in JOPI is advantageous because it facilitates passing complex structures and enables the programmer to isolate the problem space from the parallelization problem. The run-time environment for JOPI is portable, efficient and provides the necessary functionality to deploy and execute parallel Java programs. Experiments were conducted on a cluster system and a collection of heterogeneous platforms to measure JOPI's performance and compare it with MPI. The results show good performance gains using JOPI. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

OOLALA is an object-oriented linear algebra library designed to reduce the effort of software development and maintenance. In contrast with traditional (Fortran-based) libraries, it provides two high abstraction levels that significantly reduce the number of implementations necessary for particular linear algebra operations. Initial performance evaluations of a Java implementation of OOLALA show that the two high abstraction levels are not competitive with the low abstraction level of traditional libraries. These initial performance results motivate the present contribution—the characterization of a set of storage formats (data structures) and matrix properties (special features) for which implementations at the two high abstraction levels can be transformed into implementations at the low (more efficient) abstraction level. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In computational Grids, performance-hungry applications need to simultaneously tap the computational power of multiple, dynamically available sites. The crux of designing Grid programming environments stems exactly from the dynamic availability of compute cycles: Grid programming environments (a) need to be portable to run on as many sites as possible, (b) they need to be flexible to cope with different network protocols and dynamically changing groups of compute nodes, while (c) they need to provide efficient (local) communication that enables high-performance computing in the first place. Existing programming environments are either portable (Java), or flexible (Jini, Java Remote Method Invocation or (RMI)), or they are highly efficient (Message Passing Interface). No system combines all three properties that are necessary for Grid computing. In this paper, we present Ibis, a new programming environment that combines Java's ‘run everywhere’ portability both with flexible treatment of dynamically available networks and processor pools, and with highly efficient, object-based communication. Ibis can transfer Java objects very efficiently by combining streaming object serialization with a zero-copy protocol. Using RMI as a simple test case, we show that Ibis outperforms existing RMI implementations, achieving up to nine times higher throughputs with trees of objects. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Java classes are very flexible, but this comes at a price. The main cost is that every class instance must be dynamically allocated. Also, their access by reference introduces pointer de-references and complicates program analysis. These costs are particularly burdensome for small, ubiquitous data structures such as coordinates and state vectors. For such data structures a lightweight representation is desirable, allowing such data to be handled directly, similar to primitive types. A number of proposals introduce restricted or mutated variants of standard Java classes that could serve as lightweight representation, but the impact of these proposals has never been studied. Since we have implemented a Java compiler with lightweight data structures we are in a good position to do this evaluation. Our lightweight data structures are tuples. As we will show, using tuples can result in significant performance gains: for a number of existing benchmark programs we gain more than 50% in performance relative to our own compiler, and more than 20% relative to Sun's Hotspot 1.4 compiler. We expect similar performance gains for other implementations of lightweight data structures. With respect to the expressiveness of Java, lightweight variants of standard Java classes have little impact. In contrast, tuples add a different language construct that, as we will show, can lead to substantially more concise program code. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Object combining tries to put objects together that have roughly the same life times in order to reduce strain on the memory manager and to reduce the number of pointer indirections during a program's execution. Object combining works by appending the fields of one object to another, allowing allocation and freeing of multiple objects with a single heap (de)allocation. Unlike object inlining, which will only optimize objects where one has a (unique) pointer to another, our optimization also works if there is no such relation. Object inlining also directly replaces the pointer by the inlined object's fields. Object combining leaves the pointer in place to allow more combining. Elimination of the pointer accesses is implemented in a separate compiler optimization pass. Unlike previous object inlining systems, reference field overwrites are allowed and handled, resulting in much more aggressive optimization. Our object combining heuristics also allow unrelated objects to be combined, for example, those allocated inside a loop; recursive data structures (linked lists, trees) can be allocated several at a time and objects that are always used together can be combined. As Java explicitly permits code to be loaded at runtime and allows the new code to contribute to a running computation, we do not require a closed-world assumption to enable these optimizations (but it will increase performance). The main focus of object combining in this paper is on reducing object (de)allocation overhead, by reducing both garbage collection work and the number of object allocations. Reduction of memory management overhead causes execution time to be reduced by up to 35%. Indirection removal further reduces execution time by up to 6%. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

From a real-time perspective, the garbage collector (GC) introduces unpredictable pauses that are not tolerated by real-time tasks. Real-time collectors eliminate this problem but introduce a high overhead. Another approach is to use memory regions (MRs) within which allocation and deallocation is customized. This facility is supported by the memory model of the Real-Time Specification for Java (RTSJ). RTSJ imposes strict access and assignment rules to avoid both the dangling inter-region references and the delays of critical tasks of the GC. A dynamic check solution can incur high overhead, which can be reduced by taking advantage of hardware features. This paper provides an in-depth analytical investigation of the overhead introduced by dynamic assignments checks in RTSJ, describing and analysing several solutions to reduce the introduced overhead. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Java language specification states that every access to an array needs to be within the bounds of that array, i.e. between 0 and array length - 1. Different techniques for different programming languages have been proposed to eliminate explicit bounds checks. Some of these techniques are implemented in off-the-shelf Java Virtual Machines (JVMs). The underlying principle of these techniques is that bounds checks can be removed when a JVM/compiler has enough information to guarantee that a sequence of accesses (e.g. inside a for-loop) is safe (within the bounds). Most of the techniques for the elimination of array bounds checks have been developed for programming languages that do not support multi-threading and/or enable dynamic class loading. These two characteristics make most of these techniques unsuitable for Java. Techniques developed specifically for Java have not addressed the elimination of array bounds checks in the presence of indirection; that is, when the index is stored in another array (indirection array). With the objective of optimizing applications with array indirection, this paper proposes and evaluates three implementation strategies, each implemented as a Java class. The classes provide the functionality of Java arrays of type int so that objects of the classes can be used instead of indirection arrays. Each strategy enables JVMs, when examining only one of these classes at a time, to obtain enough information to remove array bounds checks. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Object-oriented languages, such as Java, encourage the use of many small objects linked together by field references, instead of a few monolithic structures. While this practice is beneficial from a program design perspective, it can slow down program execution by incurring many pointer indirections. One solution to this problem is object inlining: when the compiler can safely do so, it fuses small objects together, thus removing the reads/writes to the removed field, saving the memory needed to store the field and object header, and reducing the number of object allocations. The objective of this paper is to measure the potential for object inlining by studying the run-time behaviour of a comprehensive set of Java programs. We study the traces of program executions in order to determine which fields behave like inlinable fields. Since we are using dynamic information instead of a static analysis, our results give an upper bound on what could be achieved via a static compiler-based approach. Our experimental results measure the potential improvements attainable with object inlining, including reductions in the numbers of field reads and writes, and reduced memory usage. Our study shows that some Java programs can benefit significantly from object inlining, with close to a 10% speedup. Somewhat to our surprise, our study found one case, the db benchmark, where the most important inlinable field was the result of unusual program design, and fixing this small flaw led to both better performance and clearer program design. However, the opportunities for object inlining are highly dependent on the individual program being considered, and are in many cases very limited. Furthermore, fields that are inlinable also have properties that make them potential candidates for other optimizations such as removing redundant memory accesses. The memory savings possible through object inlining are moderate. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We introduce Jeeg, a dialect of Java based on a declarative replacement of the synchronization mechanisms of Java that results in a complete decoupling of the ‘business’ and the ‘synchronization’ code of classes. Synchronization constraints in Jeeg are expressed in a linear temporal logic, which allows one to effectively limit the occurrence of the inheritance anomaly that commonly affects concurrent object-oriented languages. Jeeg is inspired by the current trend in aspect-oriented languages. In a Jeeg program the sequential and concurrent aspects of object behaviors are decoupled: specified separately by the programmer, these are then weaved together by the Jeeg compiler. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a strategy, called almost-whole-program compilation, for extending the benefits of whole-program optimization to large collections of Java components that are packaged as a group after the development phase. This strategy has been implemented in a framework that uses Java visibility and scoping rules to transform a collection of classes into a package that is amenable to whole-program optimizations, without precluding extensions to the optimized and compiled code. Thus, it enables the Java developer to balance performance against flexibility of the program after the development phase, without compromising the design process. The transformation is shown to incur only modest performance penalties, which are more than compensated for by the interprocedural optimizations it enables. The paper concludes with experimental results showing the benefits that can be achieved using this approach. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Open Runtime Platform (ORP) is a high-performance managed runtime environment (MRTE) that features exact generational garbage collection, fast thread synchronization, and multiple coexisting just-in-time compilers (JITs). ORP was designed for flexibility in order to support experiments in dynamic compilation, garbage collection, synchronization, and other technologies. It can be built to run either Java or Common Language Infrastructure (CLI) applications, to run under the Windows or Linux operating systems, and to run on the IA-32 or Itanium processor family (IPF) architectures. Achieving high performance in a MRTE presents many challenges, particularly when flexibility is a major goal. First, to enable the use of different garbage collectors and JITs, each component must be isolated from the rest of the environment through a well-defined software interface. Without careful attention, this isolation could easily harm performance. Second, MRTEs have correctness and safety requirements that traditional languages such as C++ lack. These requirements, including null pointer checks, array bounds checks, and type checks, impose additional runtime overhead. Finally, the dynamic nature of MRTEs makes some traditional compiler optimizations, such as devirtualization of method calls, more difficult to implement or more limited in applicability. To get full performance, JITs and the core virtual machine (VM) must cooperate to reduce or eliminate (where possible) these MRTE-specific overheads. In this paper, we describe the structure of ORP in detail, paying particular attention to how it supports flexibility while preserving high performance. We describe the interfaces between the garbage collector, the JIT, and the core VM; how these interfaces enable multiple garbage collectors and JITs without sacrificing performance; and how they allow the JIT and the core VM to reduce or eliminate MRTE-specific performance issues. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Java programmers cannot help but be aware of the advent of C#, the .NET network environment, and a host of new supporting technologies, such as Web services. Before taking the big step of moving all development to a new environment, programmers will want to know what are the advantages of C# as a language over Java, and whether the new and interesting features of C# and .NET can be incorporated into existing Java software. This paper surveys the advantages of C# and then presents and evaluates experience with connecting it to Java in a variety of ways. The first way provides evidence that Java can be linked to C# at the native code level, albeit through C++ wrappers. The second is a means for retaining the useful applet feature of Java in the server-side architecture of Web services written in C#. The third is by providing a common XML-based class for the development of graphical user interfaces (GUIs), which can be incorporated into Java or C#. An added advantage of this system, called Views, is that it can run independently of the resource-intensive development environment that would otherwise be needed for using C#. A major advantage of the methods described in this paper is that in all cases the Java program is not affected by the fact that it is interfacing with C#. The paper concludes that there are many common shared technologies that bring Java and C# close together, and that innovative ways of using others can open up opportunities not hitherto imagined. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper surveys a number of the implementations of Linda that are available in Java. It provides some discussion of their strengths and weaknesses, and presents the results from benchmarking experiments using a network of commodity workstations. Some extensions to the original Linda programming model are also presented and discussed, together with examples of their application to parallel processing problems. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper we show how to utilize Java's native arrays for matrix computations. The disadvantages of Java arrays used as a 2D array for dense matrix computation are discussed and ways to improve the performance are examined. We show how to create efficient dynamic data structures for sparse matrix computations using Java's native arrays. This data structure is unique for Java and shown to be more dynamic and efficient than the traditional storage schemes for large sparse matrices. Numerical testing indicates that this new data structure, called Java Sparse Array, is competitive with the traditional Compressed Row Storage scheme on matrix computation routines. Java gives increased flexibility without losing efficiency. Compared with other object-oriented data structures Java Sparse Array is shown to have the same flexibility. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Java is normally compiled to bytecode, which is verified and then executed by the Java Virtual Machine. Bytecode produced via compilation must pass verification. The main cause of complexity for bytecode verification is subroutines, used by compilers to generate more compact code. The techniques to verify subroutines proposed in the literature reject certain programs produced by mundane compilers, are difficult to realize within an implementation of the Java Virtual Machine or are relatively complicated. This paper presents a novel technique which is very simple to understand, implement and prove sound. It is also very powerful: the set of accepted programs has a simple characterization which most likely includes all the code produced by current compilers and which enables future compilers to make more extensive use of subroutines. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The design of consistency models for both hardware and software is a difficult task. For a programming language, it is particularly difficult because the target audience for a high-level programming language is much wider than the target audience for a machine language, making usability a more important criterion. Exacerbating this problem is the reality that the programming language community has little experience designing programming language consistency models, and therefore each new attempt is very much a voyage into uncharted territory. A concrete example of the difficulties of the task is the current Java Memory Model. Although designed to be easy to use by Java programmers, it is poorly understood and at least one common idiom (the ‘double check idiom’) to exploit the model is unsafe. In this paper, we describe the design of an optimizing Java compiler that will accept either as input or as an interface implementation a consistency model for the code to be compiled. The compiler will use Shasha and Snir's delay set analysis, and our CSSA program representation to provide a canonical representation for the effects of different consistency models on optimizations and analysis. The compiler will serve as a testbed to prototype new memory models, and to measure the effects of different memory models on program performance. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We describe the parallel performance of the pure Java CartaBlanca code on heat transfer and multiphase fluid flow problems. CartaBlanca is designed for parallel computations on partitioned unstructured meshes. It uses Java's thread facility to manage computations on each of the mesh partitions. Inter-partition communications are handled by two compact objects for node-by-node communication along partition boundaries and for global reduction calculations across the entire mesh. For distributed calculations, the JavaParty package from the University of Karlsruhe is demonstrated to work with CartaBlanca. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Jackal is a fine-grained distributed shared memory implementation of the Java programming language. Jackal implements Java's memory model and allows multithreaded Java programs to run unmodified on distributed-memory systems. This paper focuses on Jackal's run-time system, which implements a multiple-writer, home-based consistency protocol. Protocol actions are triggered by software access checks that Jackal's compiler inserts before object and array references. To reduce access-check overhead, the compiler exploits source-level information and performs extensive static analysis to optimize, lift, and remove access checks. We describe optimizations for Jackal's run-time system, which mainly consists of discovering opportunities to dispense with flushing of cached data. We give performance results for different run-time optimizations, and compare their impact with the impact of one compiler optimization. We find that our run-time optimizations are necessary for good Jackal performance, but only in conjunction with the Jackal compiler optimizations described by Veldema et al. As a yardstick, we compare the performance of Java applications run on Jackal with the performance of equivalent applications that use a fast implementation of Java's Remote Method Invocation instead of shared memory. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Parallel Java environments present challenging problems for performance tools because of Java's rich language system and its multi-level execution platform combined with the integration of native-code application libraries and parallel run-time software. In addition to the desire to provide robust performance measurement and analysis capabilities for the Java language itself, the coupling of different software execution contexts under a uniform performance model needs careful consideration of how events of interest are observed and how cross-context parallel execution information is linked. This paper relates our experience in extending the TAU (Tuning and Analysis Utilities) performance system to a parallel Java environment based on mpiJava. We describe the complexities of the instrumentation model used, how performance measurements are made, and the overhead incurred. A parallel Java application simulating the game of Life is used to show the performance system's capabilities. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We present a set of language extensions that improve the expressiveness and performance of Java for scientific computation. The language extensions allow the manipulation of multi-dimensional arrays to be expressed more naturally, and to be implemented more efficiently. Furthermore, data-parallel programming is supported, allowing efficient parallelization of a large class of operations on arrays. We also provide language extensions to construct specialized array representations, such as symmetric, block, and sparse matrices. These extensions are: tuples, parameterized types, array subscript overloading, and the inline modifier. These extensions are not only useful in the construction of special array representations, but are also useful in their own right. Finally, we add complex numbers as a primitive type to the language. We evaluate our language extensions using performance results. We also compare relevant code fragments of our extended language with standard Java implementations and language extensions proposed by others. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Increasing interest is being shown in the use of Java for scientific applications. The Java Grande benchmark suite was designed with such applications primarily in mind. The perceived lack of performance of Java still deters many potential users, despite recent advances in just-in-time and adaptive compilers. There are, however, few benchmark results available comparing Java to more traditional languages such as C and Fortran. To address this issue, a subset of the Java Grande benchmarks has been re-written in C and Fortran allowing direct performance comparisons between the three languages. The performance of a range of Java execution environments, C and Fortran compilers have been tested across a number of platforms using the suite. These demonstrate that on some platforms (notable Intel Pentium) the performance gap is now quite small. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper reports on the design of a Fortran-to-Java translator whose target language is the instruction set of the Java Virtual Machine. The goal of the translator is to generate Java implementations of legacy Fortran numerical codes in a consistent and reliable fashion. The benefits of directly generating bytecode are twofold. First, compared with generating Java source code, it provides a much more straightforward and efficient mechanism for translating Fortran GOTO statements. Second, it provides a framework for pursuing various compiler optimizations, which could be beneficial not only to our project, but to the Java community as a whole. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The lack of direct support for multidimensional arrays in JavaTM has been recognized as a major deficiency in the language's applicability to numerical computing. It has been shown that, when augmented with multidimensional arrays, Java can achieve very high-performance for numerical computing through the use of compiler techniques and efficient implementations of aggregate array operations. Three approaches have been discussed in the literature for extending Java with support for multidimensional arrays: class libraries that implement these structures; extending the Java language with new syntactic constructs for multidimensional arrays that are directly translated to bytecode; and relying on the Java Virtual Machine to recognize those arrays of arrays that are being used to simulate multidimensional arrays. This paper presents a balanced presentation of the pros and cons of each technique in the areas of functionality, language and virtual machine impact, implementation effort, and effect on performance. We show that the best choice depends on the relative importance attached to the different metrics, and thereby provide a common ground for a rational discussion and comparison of the techniques. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Distributed computing has become increasingly popular in the high-performance community. Java's remote method invocation (RMI) provides a simple, yet powerful method for implementing parallel algorithms. The performance of RMI has been less than adequate, however, and object serialization is often identified as a major performance inhibitor. We believe that object serialization is best performed in the Java Virtual Machine (JVM), where information regarding object layout and hardware communication resources are readily available. We implement a subset of Java's object serialization protocol in native code, using the Java Native Interface (JNI) and JVM internals. Experiments show that our approach is up to eight times faster than Java's original object serialization protocol for array objects. Also, for linked data structures our approach obtains a moderate speedup and better scalability. Evaluation of our object serialization implementation in an RMI framework indicates that a higher throughput can be obtained. Parallel applications, written using RMI, obtain better speedups and scalability when this more efficient object serialization is used. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]