Static Validation of Barriers and Worksharing Constructs in OpenMP Applications

International audienceThe OpenMP specification requires that all threads in a team execute the same sequence of worksharing and barrier regions. An improper use of such directive may lead to deadlocks. In this paper we propose a static analysis to ensure this property is verified. The well-defined semantic of OpenMP programs makes compiler analysis more effective. We propose a new compile-time method to identify in OpenMP codes the potential improper uses of barriers and work-sharing constructs, and the execution paths that are responsible for these issues. We implemented our method in a GCC compiler plugin and show the small im-pact of our analysis on performance for NAS-OMP benchmarks and a test case for a production industrial code

A Functional Safety OpenMP∗ for Critical Real-Time Embedded Systems

OpenMP* has recently gained attention in the embedded domain by virtue of the augmentations implemented in the last specification. Yet, the language has a minimal impact in the embedded real-time domain mostly due to the lack of reliability and resiliency mechanisms. As a result, functional safety properties cannot be guaranteed. This paper analyses in detail the latest specification to determine whether and how the compliant OpenMP implementations can guarantee functional safety. Given the conclusions drawn from the analysis, the paper describes a set of modifications to the specification, and a set of requirements for compiler and runtime systems to qualify for safety critical environments. Through the proposed solution, OpenMP can be used in critical real-time embedded systems without compromising functional safety.This work was funded by the EU project P-SOCRATES (FP7-ICT-2013- 10) and the Spanish Ministry of Science and Innovation under contract TIN2015- 65316-P.Peer ReviewedPostprint (author's final draft

Safe Parallelism: Compiler Analysis Techniques for Ada and OpenMP

There is a growing need to support parallel computation in Ada to cope with the performance requirements of the most advanced functionalities of safety-critical systems. In that regard, the use of parallel programming models is paramount to exploit the benefits of parallelism. Recent works motivate the use of OpenMP for being a de facto standard in high-performance computing for programming shared memory architectures. These works address two important aspects towards the introduction of OpenMP in Ada: the compatibility of the OpenMP syntax with the Ada language, and the interoperability of the OpenMP and the Ada runtimes, demonstrating that OpenMP complements and supports the structured parallelism approach of the tasklet model. This paper addresses a third fundamental aspect: functional safety from a compiler perspective. Particularly, it focuses on race conditions and considers the fine-grain and unstructured capabilities of OpenMP. Hereof, this paper presents a new compiler analysis technique that: (1) identifies potential race conditions in parallel Ada programs based on OpenMP or Ada tasks or both, and (2) provides solutions for the detected races.This work was supported by the Spanish Ministry of Science and Innovation under contract TIN2015-65316-P, and by the FCT (Portuguese Foundation for Science and Technology) within the CISTER Research Unit (CEC/04234).Peer ReviewedPostprint (author's final draft

OpenMP tasking model for Ada: safety and correctness

22nd International Conference on Reliable Software Technologies (Ada-Europe 2017). 12 to 16, Jun, 2017. Vienna, Austria.The safety-critical real-time embedded domain increasingly demands the use of parallel architectures to fulfill performance requirements. Such architectures require the use of parallel programming models to exploit the underlying parallelism. This paper evaluates the applicability of using OpenMP, a widespread parallel programming model, with Ada, a language widely used in the safety-critical domain. Concretely, this paper shows that applying the OpenMP tasking model to exploit fine-grained parallelism within Ada tasks does not impact on programs safeness and correctness, which is vital in the environments where Ada is mostly used. Moreover, we compare the OpenMP tasking model with the proposal of Ada extensions to define parallel blocks, parallel loops and reductions. Overall, we conclude that the OpenMP tasking model can be safely used in such environments, being a promising approach to exploit fine-grain parallelism in Ada tasks, and we identify the issues which still need to be further researched.info:eu-repo/semantics/publishedVersio

ompVerify: Polyhedral Analysis for the OpenMP Programmer

This chapter is the paper we presented at the 2011 international workshop on OpenMP. Many computational scientists choose to use their own programming skills to manage the distribution of work among computer processors, rather than trust this task to an automated system that is the typical and product of the mathematics and software (known as the polyhedral framework ) that has been produced by my research community. In this work, my co-authors and I show that this same mathematics and software can be used to help programmers catch mistakes in their hand-written software for work distribution. The article is available online at http://www.irisa.fr/prive/Antoine.Morvan/publis/iwomp.pdf. --author-supplied descriptio

Hunting Superfluous Locks with Model Checking

International audienceParallelization of existing sequential programs to increase their performance and exploit recent multi and many-core architectures is a challenging but inevitable effort. One increasingly popular paral-lelization approach is based on OpenMP, which enables the designer to annotate a sequential program with constructs specifying the parallel execution of code blocks. These constructs are then interpreted by the OpenMP compiler and runtime, which assigns blocks to threads running on a parallel architecture. Although this scheme is very flexible and not (very) intrusive, it does not prevent the occurrence of synchronization errors (e.g., deadlocks) or data races on shared variables. In this paper, we propose an iterative method to assist the OpenMP parallelization by using formal methods and verification. In each iteration, potential data races are identified by applying to the OpenMP program a lockset analysis , which computes the set of shared variables that potentially need to be protected by locks. To avoid the insertion of superfluous locks, an abstract , action-based formal model of the OpenMP program is extracted and analyzed using the ACTL on-the-fly model checker of the CADP formal verification toolbox. We describe the method, compare it with existing work, and illustrate its practical use