Document number: N3971

Date: 2014-05-22

Concurrency TS Editor's Report, May 2014

by Artur Laksberg

N3970 is the Concurrency TS Draft. It is based on D3904 with the following changes as per LEWG feedback: ...

Document number: N3970

Date: 2014-05-22

Working Draft, Technical Specification for C++ Extensions for Concurrency

by Artur Laksberg

1This technical specification describes a number of concurrency extensions to the C++ Standard Library (1.2). These extensions are classes and functions that are likely to be used widely within a program and/or on the interface boundaries between libraries written by different organizations.

Document number: N4001

Date: 2014-05-23

SG5: Transactional Memory (TM) Meeting Minutes 2014/02/03-2014/05/19

by Michael Wong

Minutes for 2014/02/03 SG5 Conference Call ............................................................................... 2

Minutes for 2014/02/17 SG5 Conference Call ............................................................................... 6

Minutes for 2014/03/10 SG5 Conference Call ............................................................................... 9

Minutes for 2014/03/31 SG5 Conference Call ............................................................................. 13

Minutes for 2014/04/28 SG5 Conference Call ............................................................................. 18

Minutes for 2014/05/12 SG5 Conference Call ............................................................................. 21

Minutes for 2014/05/19 SG5 Conference Call ............................................................................. 27

Document number: N3999

Date: 2014-05-23

Standard Wording for Transactional Memory Support for C++

by Victor Luchangco, Jens Maurer, Michael Wong, et al.

1 Introduction

Transactional memory supports a programming style that is intended to facilitate parallel execution with a comparatively gentle learning curve. This document describes a proposal developed by SG5 to introduce transactional constructs into C++ as a Technical Specification.

This proposal is based in part on the Draft Specification for Transactional Constructs in C++ (Version 1.1) published by the Transactional Memory Specification Drafting Group in February 2012. It represents a pragmatic basic set of features, and omits or simplifies a number of controversial or complicated features from the Draft Specification. Our goal has been to focus SG5’s efforts towards a basic set of features that is useful and can support progress towards possible inclusion in the C++ standard.

In addition to a description of the proposal, this document contains a summary of the issues discussed Section 1.1 as well as Standard Wording for Core Section 8. Library wording is handled in a separate document.

1.1 Changes in previous revisions

N3999 (this paper): From N3919, we updated with discussion results from EWG, and the TM Evening Session of Issaquah. We considered the memory model effect from Chandler on whether a transaction that does not access any shared data induces any happens-before arcs – and in particular whether transactions that are provably thread-local must incur synchronization costs. We describe the result of that discussion in Section 7.1.

We also added Core StandardWording to support TM TS in preparation for the Draft Document. Core Standard Wording will be reviewed in a separate telecon call on June 2, and likely again at Rapperswil. Library wording is posted in N4000 and will be reviewed in Rapperswil.

Document number: N3988

Date: 2014-05-23

Towards restrict-like aliasing semantics for C++

by Hal Finkel, Hubert Tong, Chandler Carruth, Clark Nelson, Daveed Vandevoode, Michael Wong

This paper is a follow-on to N3635 after a design discussion with many compiler implementers at Issaquah, and afterwards by telecon, and specifically proposes a new alias_set attribute as a way to partition type-based aliasing to enable more fine grain control, effectively giving C++ a more complete restrict-like aliasing syntax and semantics.

Document number: N4047

Date: 2014-05-27

A Module System for C++

by Gabriel Dos Reis, Mark Hall, Gor Nishanov

This paper presents a design of a module system for C++. The proposal focuses on programmer’s view of modules (both production and consumption) and how to better support modular programming in the large, componentization, scalable compilation, and semantics-aware developer tools.

Document number: N4040

Date: 2014-05-26

Working Draft, C++ Extensions for Concepts

by Andrew Sutton

This technical specification describes extensions to the C++ Programming language (1.2) that enable the specification and checking of constraints on template arguments, and the ability to overload functions and specialize templates based on those constraints. These extensions include new syntactic forms and modifications to existing language semantics.

Document number: N4037

Date: 2014-02-14

Non-Transactional Implementation of Atomic Tree Move

by Paul E. McKenney

1 Introduction

Concurrent search trees are well understood [9, 2], as are concurrent search trees that use lightweight read-side synchronizations mechanisms [10, 11, 17, 16, 7, 1, 8] such as read-copy update (RCU) [14, 12].

However, non-transactional-memory-based algorithms that atomically move an element from one search tree to another, while avoiding delaying lockless readers, are lacking. Such algorithms are known for hash tables [18, 19]. A challenge to find such an algorithm for trees was put forward at the 2014 C++ Standards Committee meeting at Issaquah, WA USA, and this document describes one solution. As such, it is a work in progress: Future work will implement multiple solutions and compare their performance and scalability. ...

6 Summary

This paper has demonstrated a prototype solution to the Issaquah challenge of atomically moving data between two search trees without unnecessary contention.

Future work includes efficiently balancing the trees, evaluating other non-TM implementations, and comparing against TM implementations.

Document number: N4021

Date: 2014-05-21

A Proposal to Add 2D Graphics Rendering and Display to C++, Revision 1

by Michael B. McLaughlin, Herb Sutter and Jason Zink

The goal of this proposal is to define a 2D drawing API for the C++ programming language. This proposal is a revision of N3888, which was presented at the meeting of SG13 at the Issaquah meeting in February 2014. This proposal aims to provide a clean, modern C++ API that builds on the N3888 API and incorporates the feedback on it. [Note: The N3888 API was a mechanical transformation of the cairo graphics library. Cairo is a comprehensive, cross-platform, widely-used, mature 2D graphics library written in C with an object-oriented style. -- end note]

Document number: N4013

Date: 2014-05-26

Atomic operations on non-atomic data

by Hans-J. Boehm

Here we address the question of whether there should be some mechanism for applying atomic operations to non-atomic data. As pointed out in the next section, we address a somewhat different set of problems from prior discussion of non-atomic operations on atomic data (c.f. the last part of  N3710 or the Issaquah discussion.