Using variadic macros -- Andrzej Krzemieński

By Blog Staff | Jun 19, 2014 02:45 AM | Tags: None

The latest from the desk of Andrzej:

Using variadic macros

by Andrzej Krzemieński

From the article:

But what struck me was something different. Why is it only some compilers that rejected my code. Why did most of the other compilers accept my apparently buggy code and produced the right result?

The answer is in the title of this post. Boost.StaticAssert is clever and wherever possible it uses variadic macros. ... it is now OK: all these arguments along with the separating commas are forwarded further (e.g., to static_assert) to the code that knows how to interpret these tokens. This is a very nice usage of variadic macros.

CppCon Program Preview, 6 of N -- Boris Kolpackov

By Blog Staff | Jun 17, 2014 04:24 AM | Tags: None

More CppCon 2014 accepted talks have just been announced, below. For past announcements about the conference program, see also:

• CppCon Program Preview, 5 of N
• CppCon Program Preview, 4 of N
• CppCon Program Preview, 3 of N
• CppCon Program Preview, 2 of N
• CppCon Program Preview, 1 of N
• CppCon 2104: Initial Partial Topics and Speakers

Early Bird registration is available until June 30.

CppCon Program Preview, 6 of N

by Boris Kolpackov

From the announcement:

Stefanus Du Toit: “Hourglass Interfaces for C++ APIs”
Pedro Ramalhete, Andreia Correia: “How to Make Your Data Structures Wait-Free for Reads”
Gor Nishanov: “await 2.0: Stackless Resumable Functions”
Fedor Pikus: “Where did My Performance Go? (Scaling Visualization in Concurrent C++ Programs)”
Łukasz Mendakiewicz: “Viewing the World Through Array-Shaped Glasses”

 

Stefanus Du Toit: “Hourglass Interfaces for C++ APIs”

C++ provides a much richer set of abstractions than C. Classes, templates, overloading, and other core C++ features can be leveraged for more readable syntax, better compile time typechecking, more open ended genericity and improved modularity. On the flip side, C89 still boasts some advantages over C++, especially when viewed through a pragmatic lens. C ABIs on many platforms have been stable for decades, practically every language supports binding to C code through foreign function interfaces, and including nearly any C89 header has a negligible effect on compile time on modern computers. The Hourglass pattern provides the best of both worlds. It’s a way to structure libraries that retains the pragmatic benefits of C89 while still providing C++’s richness both at an interface and implementation level. It makes providing bindings from other languages to C++ libraries easier, and insulates from ABI issues such as incompatibilities between debug and release variants of runtimes. This talk provides an overview of the pattern, teaches practical techniques for its implementation using C++98 and C++11, and shares experience from using the pattern in real world projects.

Speaker’s bio: Stefanus Du Toit is a Software Lead at Thalmic Labs, where he enables amazing gestural experiences using the Myo armband. Stefanus previously worked as a Software Architect and Software Development Manager at Intel Corporation, and co-founded RapidMind (acquired by Intel), a startup that targeted GPUs and other processors using standard C++. Stefanus served on the C++ standards committee as Project Editor for C++14 and as Committee Secretary. He lives in Kitchener-Waterloo, Ontario, Canada and holds a BMath CS from the University of Waterloo.

 

Pedro Ramalhete, Andreia Correia: “How to Make Your Data Structures Wait-Free for Reads”

In this talk we will describe a new concurrency control algorithm with Blocking write operations and Wait-Free Population Oblivious read operations, which we named the Left-Right algorithm. We will show a new pattern where this algorithm is applied, which requires using two instances of a given resource, and can be used for any data structure, allowing concurrent access to it similarly to a Reader-Writer lock, but in a non-blocking manner for reads, including safe memory management without needing a GC.

Speaker’s bio: Pedro Ramalhete has a PhD in Particle Physics for research done at CERN. Most of the research itself required programming in C++, and he also had a major participation in the coding of the experiment’s data acquisition and decoding software in C and C++. Pedro is currently working at Cisco writing networking software, with emphasis on real-time concurrent synchronization techniques, and wait-free/lock-free data structures.

 

Gor Nishanov: “await 2.0: Stackless Resumable Functions”

When dealing with the task/future based asynchronous model, developers need to write lambda-heavy continuation code with potentially multiple nesting lambdas. This makes the code less readable and not very pleasant to write. Stackless resumable functions allow developers to use more natural imperative coding style and provide performance benefits that are not possible with library-only solutions.

Speaker’s bio: Gor Nishanov is a Principal Software Design Engineer on the Microsoft C++ team. He works on the ‘await’ feature. Prior to joining the C++ team, Gor was working on distributed systems in Windows Clustering team.

Fedor Pikus: “Where did My Performance Go? (Scaling Visualization in Concurrent C++ Programs)”

High performance is one of the main reasons programmers choose C++ for their applications. If you are writing in C++, odds are you need every bit of computing power your hardware can provide. Today, this means writing multi-threaded programs to effectively utilize the multiple CPU cores that the hardware manufacturers keep adding. Everyone knows that writing multi-threaded programs is hard. Writing correct multi-threaded programs is even harder. Only after spending countless hours debugging race conditions and weird intermittent bugs do many programmers learn that writing efficient multi-threaded programs is harder yet. Have you ever wanted to see what are all your threads doing when they should be busy computing? This talk will show you how. We begin by studying several techniques necessary for collecting large amounts of data from the running program very efficiently, with little overhead and minimal disruption to the program itself. We will cover efficient thread-safe memory management and efficient thread-safe disk I/O. Along the way we dabble in lock-free programming just enough to meet our needs, lest the subject will spiral into an hour-long talk of its own. With all these techniques put together, we can collect information about what each thread is doing, which threads are computing and what exactly, and which threads are slacking off waiting on locks, and do it at the time scale of tens of microseconds if necessary. Then we process the collected data and create a timeline that shows exactly what the program was doing at every moment in time.

 

Łukasz Mendakiewicz: “Viewing the World Through Array-Shaped Glasses”

It’s agreed among experts that the most performant data structure in C++ is an array. Or a vector. Or a dynarray. Indeed, until recently there was no standardized approach in C++ to view these types in a uniform manner. It was even murkier when the data had logically more than one dimension. This talk is an introduction to the new features proposed for C++17 in N3851 bringing all contiguous data into harmony and lifting it to higher dimensions: index, bounds, array_view and more. Attendees will also learn how indexable algorithms differ from the traditional elemental ones, and what does it mean for parallelism.

Speaker’s bio: Łukasz Mendakiewicz is a software engineer at Microsoft, where he focuses on the customer experience with parallel programming models for C++. He is especially interested in GPGPU acceleration, and puts this passion to work on C++ AMP. He holds an M.S. in Computer Science from AGH UST in Krakow, Poland.

Masking a Class in Boost Graph, Part 3: Finding the Path -- Vadim Androsov

By Blog Staff | Jun 16, 2014 07:19 AM | Tags: intermediate

Part 3 of Vadim's experience report about using Boost's graph support in an existing game app:

Masking a Class in Boost Graph. Part 3: Finding the Path

by Vadim Androsov

From the article:

In the previous articles of the series we’ve reviewed the adaptive process of the square game field for concepts of boost graphs. Now we’ll consider the process of finding the path in the square field. Implementation of boost search allows adapting the algorithm quite accurately. In this article we’ll provide just one example of such parameterization – an ability to create various lengths of graph edges. ...

Game Changer -- Tony DaSilva

By Blog Staff | Jun 16, 2014 06:25 AM | Tags: None

A little more fodder for those still trying to get their management or team to adopt modern C++:

Game Changer

by Tony DaSilva

From the article:

Even though I’m a huge fan of the man, I was quite skeptical when I heard Bjarne Stroustrup enunciate: "C++ feels like a new language". Of course, Bjarne was talking about the improvements brought into the language by the C++11 standard.

Well, after writing C++11 production code for almost 2 years now (17 straight sprints to be exact), I’m no longer skeptical. ... It seems that the authors of the “High Integrity C++” coding standard agree with my assessment. ...

Quick Q: Is unique_ptr guaranteed to store nullptr after move? -- StackOverflow

By Blog Staff | Jun 13, 2014 03:10 AM | Tags: basics

Quick A: Yes. Otherwise, it would be unsafe and a lot less unique.

From SO:

Is unique_ptr guaranteed to store nullptr after move?

std::unique_ptr<int> p1{new int{23}};
std::unique_ptr<int> p2{std::move(p1)};
assert(!p1); // is this always true?

Modernizing Legacy C++ Code -- James McNellis

By NoSenseEtAl | Jun 13, 2014 12:06 AM | Tags: None

From Techdays 2014 the Netherlands:

Modernizing Legacy C++ Code

by James McNellis

In this session, James McNellis, a developer on the Visual C++ libraries team, will share his experience using elements of modern C++ to improve a large legacy code base. Learn how to apply principles of modern C++ to gradually improve the quality of legacy code and improve maintainability and debuggability

CMake 3.0.0 Released

By Hauke | Jun 12, 2014 05:52 PM | Tags: None

A new major version of CMake, v3.0.0 has been released. CMake is a tool for cross platform C/C++ (and more) build poject configuration.

Version 3.0.0 contains many improvements. To get an idea of the recent changes, as well as the improvements of CMake over the last months and years, take a look at the following links:

• Release announcements/changes
• Modern tutorial

EuroLLVM videos and slides now available

By Blog Staff | Jun 12, 2014 02:57 PM | Tags: None

All available videos are now posted from this April's EuroLLVM conference.

The conference included the following C++-related sesssions. Note that only the first two have video, all have slides or other materials.

Keynote: What's new in C++14, and how you can take advantage of it (slides) -- Marshall Clow

Portable Native Client. Fast, Secure, Simple: Pick Three. (slides) -- JF Bastien

clang-tidy - Lint-like checks and beyond (slides) -- Daniel Jasper

Refactoring a large C++ codebase using clang (slides) -- Nick Lewycky

Async Magic - std::async in C++ and its consequences for optimizations (slides) -- Tobias Rieger

Intel Clang-Based C++ Compiler (poster) -- Andrey Bokhanko

Clang as a C++ front-end for Frama-C and VeriFast (poster) -- Virgile Prevosto, Franck Védrine, Bart Jacobs and Gijs van Spauwen

IBM XL C/C++ 13.1 supports =default/=delete, constexpr, nullptr

By Blog Staff | Jun 12, 2014 02:49 PM | Tags: None

XL C/C++ and AIX and Linux is now available:

XL C/C++ for AIX and Linux, V13.1 Now Released!

We're happy to announce the release of the XL C/C++ for AIX, V13.1 and XL C/C++ for Linux, V13.1 compilers!  The V13.1 release delivers POWER8 exploitation and new compiler and language features.

From the announcement details:

IBM® XL C/C++ for Linux™ is a standards-based, high performance C/C++ compiler with advanced optimizing features. XL C/C++ for Linux, V13.1 delivers a number of new features and enhancements:

• Exploitation of the latest IBM POWER8™ architecture
• Support for additional features in C11 and C++11, the current standards for the C and C++ programming languages
• Partial support for the OpenMP 4.0 industry specification
• Compile and runtime performance improvements
• Additional performance options
• New program diagnostics and error detection features

...

C++11 programming standard

C++11 is the latest standard for the C++ programming language, published as ISO/IEC 14882:2011. With V13.1, partial support for the C++11 standard continues with the implementation of the following features:

Defaulted and deleted functions

This feature introduces two new forms of function declarations to define explicitly defaulted functions and deleted functions. For the explicitly defaulted functions, the compiler generates the default implementations, which are more efficient than manually programmed implementations. The compiler disables the deleted functions to avoid calling unwanted functions.

You can use the -qlanglvl=defaultanddelete option to enable this feature.

Generalized constant expressions

The generalized constant expressions feature extends the set of expressions permitted within constant expressions. The implementation of this feature in XL C/C++ V12.1 was a partial implementation of what is defined in the C++11 standard. In this release, enhancements are made to support user-defined constexpr objects and constexpr pointers or references to constexpr functions and objects.

You can use the -qlanglvl=constexpr option to enable this feature.

The nullptr keyword

This feature introduces nullptr as a null pointer constant. The nullptr constant can be distinguished from integer 0 for overloaded functions. The constants of 0 and NULL are treated as the integer type for overloaded functions, whereas nullptr can be implicitly converted to only the pointer type, pointer-to-member type, and bool type.

You can use the -qlanglvl=nullptr option to enable this feature.

N4058: Atomic Smart Pointers -- Herb Sutter

By Blog Staff | Jun 12, 2014 10:21 AM | Tags: None

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4058

Date: 2014-06-12

Atomic Smart Pointers

by Herb Sutter

Excerpt:

We encourage that modern C++ code should avoid all uses of owning raw pointers and explicit delete. Instead, programmers should use unique_ptr and shared_ptr (with weak_ptr), as this is known to lead to simpler and leak-free memory-safe code. This is especially important when lifetimes are unstructured or nondeterministic, which arises especially in concurrent code, and it has long been well-known that the smart pointers would be useful there; for an example, see [1].

Unfortunately, lock-free code is still mostly forced to use owning raw pointers. Our unique_ptr, shared_ptr, and weak_ptr would directly benefit lock-free code just as they do regular code (see next section), but they are not usable easily or at all in lock-free code because we do not support atomic<unique_ptr<T>>, atomic<shared_ptr<T>>, and atomic<weak_ptr<T>>.

...

If we had atomic<unique_ptr<T>> we could (and should) write the following equivalent code that is safer, no slower, and less error-prone because we can directly express the unique ownership semantics including ownership transfer:

atomic<unique_ptr<X>> p_root;
void producer() {
    auto temp = make_unique<X>();
    load_from_disk_and_store_in( *temp ); // build data structure
    p_root = move(temp);                  // atomically publish it
}

This righteous code should be supported...