1,014 research outputs found
Maintaining consistency in distributed systems
In systems designed as assemblies of independently developed components, concurrent access to data or data structures normally arises within individual programs, and is controlled using mutual exclusion constructs, such as semaphores and monitors. Where data is persistent and/or sets of operation are related to one another, transactions or linearizability may be more appropriate. Systems that incorporate cooperative styles of distributed execution often replicate or distribute data within groups of components. In these cases, group oriented consistency properties must be maintained, and tools based on the virtual synchrony execution model greatly simplify the task confronting an application developer. All three styles of distributed computing are likely to be seen in future systems - often, within the same application. This leads us to propose an integrated approach that permits applications that use virtual synchrony with concurrent objects that respect a linearizability constraint, and vice versa. Transactional subsystems are treated as a special case of linearizability
A speculative execution approach to provide semantically aware contention management for concurrent systems
PhD ThesisMost modern platforms offer ample potention for parallel execution of concurrent programs yet concurrency control is required to exploit parallelism while maintaining program correctness. Pessimistic con-
currency control featuring blocking synchronization and mutual ex-
clusion, has given way to transactional memory, which allows the
composition of concurrent code in a manner more intuitive for the
application programmer. An important component in any transactional memory technique however is the policy for resolving conflicts
on shared data, commonly referred to as the contention management
policy.
In this thesis, a Universal Construction is described which provides
contention management for software transactional memory. The technique differs from existing approaches given that multiple execution
paths are explored speculatively and in parallel. In the resolution of
conflicts by state space exploration, we demonstrate that both concur-
rent conflicts and semantic conflicts can be solved, promoting multi-
threaded program progression.
We de ne a model of computation called Many Systems, which defines the execution of concurrent threads as a state space management
problem. An implementation is then presented based on concepts
from the model, and we extend the implementation to incorporate
nested transactions. Results are provided which compare the performance of our approach with an established contention management
policy, under varying degrees of concurrent and semantic conflicts. Finally, we provide performance results from a number of search strategies, when nested transactions are introduced
libcppa - Designing an Actor Semantic for C++11
Parallel hardware makes concurrency mandatory for efficient program
execution. However, writing concurrent software is both challenging and
error-prone. C++11 provides standard facilities for multiprogramming, such as
atomic operations with acquire/release semantics and RAII mutex locking, but
these primitives remain too low-level. Using them both correctly and
efficiently still requires expert knowledge and hand-crafting. The actor model
replaces implicit communication by sharing with an explicit message passing
mechanism. It applies to concurrency as well as distribution, and a lightweight
actor model implementation that schedules all actors in a properly
pre-dimensioned thread pool can outperform equivalent thread-based
applications. However, the actor model did not enter the domain of native
programming languages yet besides vendor-specific island solutions. With the
open source library libcppa, we want to combine the ability to build reliable
and distributed systems provided by the actor model with the performance and
resource-efficiency of C++11.Comment: 10 page
Efficient and Reasonable Object-Oriented Concurrency
Making threaded programs safe and easy to reason about is one of the chief
difficulties in modern programming. This work provides an efficient execution
model for SCOOP, a concurrency approach that provides not only data race
freedom but also pre/postcondition reasoning guarantees between threads. The
extensions we propose influence both the underlying semantics to increase the
amount of concurrent execution that is possible, exclude certain classes of
deadlocks, and enable greater performance. These extensions are used as the
basis an efficient runtime and optimization pass that improve performance 15x
over a baseline implementation. This new implementation of SCOOP is also 2x
faster than other well-known safe concurrent languages. The measurements are
based on both coordination-intensive and data-manipulation-intensive benchmarks
designed to offer a mixture of workloads.Comment: Proceedings of the 10th Joint Meeting of the European Software
Engineering Conference and the ACM SIGSOFT Symposium on the Foundations of
Software Engineering (ESEC/FSE '15). ACM, 201
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A Deterministic Multi-Way Rendezvous Library for Haskell
The advent of multicore processors requires mainstream concurrent programming languages with high level concurrency constructs and effective debugging techniques. Unfortunately, many concurrent programming languages are non-deterministic and allow data races. We present a deterministic concurrent communication library for an existing multi-threaded language. We implemented the SHIM communication model in the Haskell functional language, which supports asynchronous communication and transactional memory. The SHIM model uses multi-way rendezvous to guarantee determinism. We describe two implementations of the model in Haskell, demonstrating the ease of writing such a library. We illustrate our library with examples and experimentally compare two implementations. We also compare our new model with equivalent sequential programs and parallel versions using Haskell's existing concurrency mechanisms
The parallel event loop model and runtime: a parallel programming model and runtime system for safe event-based parallel programming
Recent trends in programming models for server-side development have shown an increasing popularity of event-based single- threaded programming models based on the combination of dynamic languages such as JavaScript and event-based runtime systems for asynchronous I/O management such as Node.JS. Reasons for the success of such models are the simplicity of the single-threaded event-based programming model as well as the growing popularity of the Cloud as a deployment platform for Web applications. Unfortunately, the popularity of single-threaded models comes at the price of performance and scalability, as single-threaded event-based models present limitations when parallel processing is needed, and traditional approaches to concurrency such as threads and locks don't play well with event-based systems. This dissertation proposes a programming model and a runtime system to overcome such limitations by enabling single-threaded event-based applications with support for speculative parallel execution. The model, called Parallel Event Loop, has the goal of bringing parallel execution to the domain of single-threaded event-based programming without relaxing the main characteristics of the single-threaded model, and therefore providing developers with the impression of a safe, single-threaded, runtime. Rather than supporting only pure single-threaded programming, however, the parallel event loop can also be used to derive safe, high-level, parallel programming models characterized by a strong compatibility with single-threaded runtimes. We describe three distinct implementations of speculative runtimes enabling the parallel execution of event-based applications. The first implementation we describe is a pessimistic runtime system based on locks to implement speculative parallelization. The second and the third implementations are based on two distinct optimistic runtimes using software transactional memory. Each of the implementations supports the parallelization of applications written using an asynchronous single-threaded programming style, and each of them enables applications to benefit from parallel execution
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