Access Annotation for Safe Program Parallelization

Part 1: Session 1: Parallel Programming and AlgorithmsInternational audienceThe safety of speculative parallelization depends on monitoring all program access to shared data. The problem is especially difficult in software-based solutions. Till now, automatic techniques use either program instrumentation, which can be costly, or virtual memory protection, which incurs false sharing. In addition, not all access requires monitoring. It is worth considering a manual approach in which programmers insert access annotations to reduce the cost and increase the precision of program monitoring.This paper presents an interface for access annotation and two techniques to check the correctness of user annotation, i.e. whether all parallel executions are properly monitored and guaranteed to produce the sequential result. It gives a quadratic-time algorithm to check the exponential number of parallel interleavings. The paper then uses the annotation interface to parallelize several programs with uncertain parallelism. It demonstrates the efficiency of program monitoring by a performance comparison with OpenMP, which does not monitor data access or guarantee safety

Automated deadlock detection in synchronized reentrant multithreaded call-graphs

In this paper we investigate the synchronization of multithreaded call graphs with reentrance similar to call graphs in Java programs. We model the individual threads as Visibly Pushdown Automata (VPA) and analyse the reachability of a state in the product automaton by means of a Context Free Language (CFL) which captures the synchronized interleaving of threads. We apply this CFL-reachability analysis to detect deadlock

Motivation losses in task-performing groups: A social dilemma analysis.

Theory developed to account for behavior in social dilemmas—situations in which - the rational pursuit of self-interest can lead to collective disaster—was applied to the analysis of group motivation losses. Two group motivation loss effects demonstrated in previous research, the social-loafing effect and the free-rider effect, were shown to follow from social dilemma theories. An experiment was performed to empirically demonstrate a third motivation loss effect, termed the sucker effect. It was hypothesized that group members would reduce their efforts if they had a capable partner.who free rode on their efforts, that is, who was capable of contributing to the group but would not. This prediction was confirmed. The effect was particularly strong in males. Potential remedies for such motivation losses were discussed

Allocating memory in a lock-free manner

The potential of multiprocessor systems is often not fully realized by their system services. Certain synchronization methods, such as lock-based ones, may limit the parallelism. It is significant to see the impact of wait/lock-free synchronization design in key services for multiprocessor systems, such as the memory allocation service. Efficient, scalable memory allocators for multithreaded applications on multiprocessors is a significant goal of recent research projects. We propose a lock-free memory allocator, to enhance the parallelism in the system. Its architecture is inspired by Hoard, a successful concurrent memory allocator, with a modular, scalable design that preserves scalability and helps avoiding false-sharing and heap blowup. Within our effort on designing appropriate lock-free algorithms to construct this system, we propose a new non-blocking data structure called flat-sets, supporting conventional “internal” operations as well as “inter-object” operations, for moving items between flat-sets. We implemented the memory allocator in a set of multiprocessor systems (UMA Sun Enterprise 450 and ccNUMA Origin 3800) and studied its behaviour. The results show that the good properties of Hoard w.r.t. false-sharing and heap-blowup are preserved, while the scalability properties are enhanced even further with the help of lock-free synchronization