Modular termination verification for non-blocking concurrency

© Springer-Verlag Berlin Heidelberg 2016.We present Total-TaDA, a program logic for verifying the total correctness of concurrent programs: that such programs both terminate and produce the correct result. With Total-TaDA, we can specify constraints on a thread’s concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for nonblocking algorithms, e.g. a counter and a stack. Our specifications can express lock- and wait-freedom. More generally, they can express that one operation cannot impede the progress of another, a new non-blocking property we call non-impedance. Moreover, our approach is modular. We can verify the operations of a module independently, and build up modules on top of each other

Single-Producer/Single-Consumer Queues on Shared Cache Multi-Core Systems

Using efficient point-to-point communication channels is critical for implementing fine grained parallel program on modern shared cache multi-core architectures. This report discusses in detail several implementations of wait-free Single-Producer/Single-Consumer queue (SPSC), and presents a novel and efficient algorithm for the implementation of an unbounded wait-free SPSC queue (uSPSC). The correctness proof of the new algorithm, and several performance measurements based on simple synthetic benchmark and microbenchmark, are also discussed

Modular termination veri cation for non-blocking concurrency (extended version)

We present Total-TaDA, a program logic for verifying the total correctness of concurrent programs: that such programs both terminate and produce the correct result. With Total-TaDA, we can specify constraints on a thread's concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for nonblocking algorithms, e.g. a counter and a stack. Our speci cations can express lock- and wait-freedom. More generally, they can express that one operation cannot impede the progress of another, a new non-blocking property we call non-impedance. Moreover, our approach is modular. We can verify the operations of a module independently, and build up modules on top of each other

Reasoning with time and data abstractions

In this thesis, we address the problem of verifying the functional correctness of concurrent programs, with emphasis on fine-grained concurrent data structures. Reasoning about such programs is challenging since data can be concurrently accessed by multiple threads: the reasoning must account for the interference between threads, which is often subtle. To reason about interference, concurrent operations should either be at distinct times or on distinct data. We present TaDA, a sound program logic for verifying clients and implementations that use abstract specifications that incorporate both abstract atomicity—the abstraction that operations take effect at a single, discrete instant in time—and abstract disjointness—the abstraction that operations act on distinct data resources. Our key contribution is the introduction of atomic triples, which offer an expressive approach for specifying program modules. We also present Total-TaDA, a sound extension of TaDA with which we can verify total correctness of concurrent programs, i.e. that such programs both produce the correct result and terminate. With Total-TaDA, we can specify constraints on a thread’s concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for nonblocking algorithms and express lock- and wait-freedom. More generally, the abstract specifications can express that one operation cannot impede the progress of another, a new non-blocking property that we call non-impedance. Finally, we describe how to extend TaDA for proving abstract atomicity for data structures that make use of helping—where one thread is performing an abstract operation on behalf of another—and speculation—where an abstract operation is determined by future behaviour.Open Acces

Advanced synchronization techniques for task-based runtime systems

Task-based programming models like OmpSs-2 and OpenMP provide a flexible data-flow execution model to exploit dynamic, irregular and nested parallelism. Providing an efficient implementation that scales well with small granularity tasks remains a challenge, and bottlenecks can manifest in several runtime components. In this paper, we analyze the limiting factors in the scalability of a task-based runtime system and propose individual solutions for each of the challenges, including a wait-free dependency system and a novel scalable scheduler design based on delegation. We evaluate how the optimizations impact the overall performance of the runtime, both individually and in combination. We also compare the resulting runtime against state of the art OpenMP implementations, showing equivalent or better performance, especially for fine-grained tasks.This project is supported by the European Union’s Horizon 2020 Research and Innovation programme under grant agreement No.s 754304 (DEEP-EST), by the Spanish Ministry of Science and Innovation (contract PID2019-107255GB and TIN2015-65316P) and by the Generalitat de Catalunya (2017-SGR-1414).Peer ReviewedPostprint (author's final draft

Efficient almost wait-free parallel accesible dynamic hashtables

Abstract In multiprogrammed systems, synchronization often turns out to be a performance bottleneck and the source of poor fault-tolerance. Wait-free and lock-free algorithms can do without locking mechanisms, and therefore do not suffer from these problems. We present an efficient almost wait-free algorithm for parallel accessible hashtables, which promises more robust performance and reliability than conventional lock-based implementations. Our solution is as efficient as sequential hashtables. It can easily be implemented using C-like languages and requires on average only constant time for insertion, deletion or accessing of elements. Apart from that, our new algorithm allows the hashtables to grow and shrink dynamically when needed. A true problem of lock-free algorithms is that they are hard to design correctly, even when apparently straightforward. Ensuring the correctness of the design at the earliest possible stage is a major challenge in any responsible system development. Our algorithm contains 81 atomic statements. In view of the complexity of the algorithm and its correctness properties, we turned to the interactive theorem prover PVS for mechanical support. We employ standard deductive verification techniques to prove around 200 invariance properties of our almost wait-free algorithm, and describe how this is achieved using the theorem prover PVS. CR Subject Classification (1991): D.1 Programming techniques AMS Subject Classification (1991): 68Q22 Distributed algorithms, 68P20 Information storage and retrieval Keywords & Phrases: Hashtables, Distributed algorithms, Lock-free, Wait-fre

Adaptive software transactional memory : dynamic contention management

This thesis addresses the problem of contention management in Software Transactional Memory (STM), which is a scheme for managing shared memory in a concurrent programming environment. STM views shared memory in a way similar to that of a database; read and write operations are handled through transactions, with changes to the shared memory becoming permanent through commit operations. Research on this subject reveals that there are currently varying methods for collision detection, data validation, and contention management, each of which has different situations in which they become the preferred method. This thesis introduces a dynamic contention manager that monitors current performance and chooses the proper contention manager accordingly. Performance calculations, and subsequent polling of the underlying library, are minimized. As a result, this adaptive contention manager yields a higher average performance level over time when compared with existing static implementations