4,258 research outputs found
Handling Parallelism in a Concurrency Model
Programming models for concurrency are optimized for dealing with
nondeterminism, for example to handle asynchronously arriving events. To shield
the developer from data race errors effectively, such models may prevent shared
access to data altogether. However, this restriction also makes them unsuitable
for applications that require data parallelism. We present a library-based
approach for permitting parallel access to arrays while preserving the safety
guarantees of the original model. When applied to SCOOP, an object-oriented
concurrency model, the approach exhibits a negligible performance overhead
compared to ordinary threaded implementations of two parallel benchmark
programs.Comment: MUSEPAT 201
Enhancing the performance of Decoupled Software Pipeline through Backward Slicing
The rapidly increasing number of cores available in multicore processors does
not necessarily lead directly to a commensurate increase in performance:
programs written in conventional languages, such as C, need careful
restructuring, preferably automatically, before the benefits can be observed in
improved run-times. Even then, much depends upon the intrinsic capacity of the
original program for concurrent execution. The subject of this paper is the
performance gains from the combined effect of the complementary techniques of
the Decoupled Software Pipeline (DSWP) and (backward) slicing. DSWP extracts
threadlevel parallelism from the body of a loop by breaking it into stages
which are then executed pipeline style: in effect cutting across the control
chain. Slicing, on the other hand, cuts the program along the control chain,
teasing out finer threads that depend on different variables (or locations).
parts that depend on different variables. The main contribution of this paper
is to demonstrate that the application of DSWP, followed by slicing offers
notable improvements over DSWP alone, especially when there is a loop-carried
dependence that prevents the application of the simpler DOALL optimization.
Experimental results show an improvement of a factor of ?1.6 for DSWP + slicing
over DSWP alone and a factor of ?2.4 for DSWP + slicing over the original
sequential code
A distributed Real-Time Java system based on CSP
CSP is a fundamental concept for developing software for distributed real time systems. The CSP paradigm constitutes a natural addition to object orientation and offers higher order multithreading constructs. The CSP channel concept that has been implemented in Java deals with single- and multi-processor environments and also takes care of the real time priority scheduling requirements. For this, the notion of priority and scheduling has been carefully examined and as a result it was reasoned that priority scheduling should be attached to the communicating channels rather than to the processes. In association with channels, a priority based parallel construct is developed for composing processes: hiding threads and priority indexing from the user. This approach simplifies the use of priorities for the object oriented paradigm. Moreover, in the proposed system, the notion of scheduling is no longer connected to the operating system but has become part of the application instead
Sound Static Deadlock Analysis for C/Pthreads (Extended Version)
We present a static deadlock analysis approach for C/pthreads. The design of
our method has been guided by the requirement to analyse real-world code. Our
approach is sound (i.e., misses no deadlocks) for programs that have defined
behaviour according to the C standard, and precise enough to prove
deadlock-freedom for a large number of programs. The method consists of a
pipeline of several analyses that build on a new context- and thread-sensitive
abstract interpretation framework. We further present a lightweight dependency
analysis to identify statements relevant to deadlock analysis and thus speed up
the overall analysis. In our experimental evaluation, we succeeded to prove
deadlock-freedom for 262 programs from the Debian GNU/Linux distribution with
in total 2.6 MLOC in less than 11 hours
Boosting Multi-Core Reachability Performance with Shared Hash Tables
This paper focuses on data structures for multi-core reachability, which is a
key component in model checking algorithms and other verification methods. A
cornerstone of an efficient solution is the storage of visited states. In
related work, static partitioning of the state space was combined with
thread-local storage and resulted in reasonable speedups, but left open whether
improvements are possible. In this paper, we present a scaling solution for
shared state storage which is based on a lockless hash table implementation.
The solution is specifically designed for the cache architecture of modern
CPUs. Because model checking algorithms impose loose requirements on the hash
table operations, their design can be streamlined substantially compared to
related work on lockless hash tables. Still, an implementation of the hash
table presented here has dozens of sensitive performance parameters (bucket
size, cache line size, data layout, probing sequence, etc.). We analyzed their
impact and compared the resulting speedups with related tools. Our
implementation outperforms two state-of-the-art multi-core model checkers (SPIN
and DiVinE) by a substantial margin, while placing fewer constraints on the
load balancing and search algorithms.Comment: preliminary repor
Slicing of Concurrent Programs and its Application to Information Flow Control
This thesis presents a practical technique for information flow control for concurrent programs with threads and shared-memory communication. The technique guarantees confidentiality of information with respect to a reasonable attacker model and utilizes program dependence
graphs (PDGs), a language-independent representation of information flow in a program
Ada (trademark) projects at NASA. Runtime environment issues and recommendations
Ada practitioners should use this document to discuss and establish common short term requirements for Ada runtime environments. The major current Ada runtime environment issues are identified through the analysis of some of the Ada efforts at NASA and other research centers. The runtime environment characteristics of major compilers are compared while alternate runtime implementations are reviewed. Modifications and extensions to the Ada Language Reference Manual to address some of these runtime issues are proposed. Three classes of projects focusing on the most critical runtime features of Ada are recommended, including a range of immediately feasible full scale Ada development projects. Also, a list of runtime features and procurement issues is proposed for consideration by the vendors, contractors and the government
Fault Localization in Multi-Threaded C Programs using Bounded Model Checking (extended version)
Software debugging is a very time-consuming process, which is even worse for
multi-threaded programs, due to the non-deterministic behavior of
thread-scheduling algorithms. However, the debugging time may be greatly
reduced, if automatic methods are used for localizing faults. In this study, a
new method for fault localization, in multi-threaded C programs, is proposed.
It transforms a multi-threaded program into a corresponding sequential one and
then uses a fault-diagnosis method suitable for this type of program, in order
to localize faults. The code transformation is implemented with rules and
context switch information from counterexamples, which are typically generated
by bounded model checkers. Experimental results show that the proposed method
is effective, in such a way that sequential fault-localization methods can be
extended to multi-threaded programs.Comment: extended version of paper published at SBESC'1
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