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Fixing exception safety in our task_sequencer -- Raymond Chen

By Blog Staff | Jun 9, 2025 05:07 PM | Tags: None

Some time ago, we developed a task_sequencer class for running asynchronous operations in sequence. There’s a problem with the implementation of QueueTaskAsync: What happens if an exception occurs?

Fixing Exception Safety in our task_sequencer

by Raymond Chen

From the article:

Let’s look at the various places an exception can occur in QueueTaskAsync.

    template<typename Maker>
    auto QueueTaskAsync(Maker&& maker) ->decltype(maker())
    {
        auto current = std::make_shared<chained_task>();
        auto previous = [&]
        {
            winrt::slim_lock_guard guard(m_mutex);
            return std::exchange(m_latest, current); ← oops
        }();

        suspender suspend;

        using Async = decltype(maker());
        auto task = [](auto&& current, auto&& makerParam,
                       auto&& contextParam, auto& suspend)
                    -> Async
        {
            completer completer{ std::move(current) };
            auto maker = std::move(makerParam);
            auto context = std::move(contextParam);

            co_await suspend;
            co_await context;
            co_return co_await maker();
        }(current, std::forward<Maker>(maker),
          winrt::apartment_context(), suspend);

        previous->continue_with(suspend.handle);

        return task;
    }

If an exception occurs at make_shared, then no harm is done because we haven’t done anything yet.

If an exception occurs when starting the lambda task, then we are in trouble. We have already linked the current onto m_latest, but we will never call continue_with(), so the chain of tasks stops making progress.

To fix this, we need to delay hooking up the current to the chain of chained_tasks until we are sure that we have a task to chain.

CppCon 2024 Cost of C++ Abstractions in C++ Embedded Systems -- Marcell Juhasz

By Blog Staff | Jun 6, 2025 01:00 PM | Tags: None

Registration is now open for CppCon 2025! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting videos of some of the top-rated talks from last year's conference. Here’s another CppCon talk video we hope you will enjoy – and why not register today for CppCon 2025!

Cost of C++ Abstractions in C++ Embedded Systems

by Marcell Juhasz

Summary of the talk:

This session will feature detailed case studies that measure the overhead associated with common programming abstractions in the context of embedded systems. By examining both compile-time and run-time implications, attendees will gain valuable insights into how these abstractions impact system resources like memory usage and execution speed.

Key areas of exploration will include:

Encapsulation: Assessing the cost of data hiding and interface protection depending on implementation strategies.
Inheritance: Evaluating the costs and benefits of using class hierarchies in environments where memory and processing power are limited.
Polymorphism: Comparing run-time polymorphism via virtual functions to compile-time alternatives like templates and concepts, analyzing their respective impacts on performance and flexibility.

Through empirical data and performance metrics, participants will observe how traditional object-oriented techniques affect resource utilization. The discussion will also cover the advantages and trade-offs of these techniques, providing a balanced view of their impact on embedded systems.

Designed for developers and system architects working within the constraints of embedded systems, this talk aims to provide valuable insights into making informed decisions about when and how to use specific programming abstractions. Attendees will leave with a clearer perspective on optimizing their code for maximum efficiency, armed with practical knowledge about the trade-offs involved in adopting various software design paradigms.

How to Join or Concat Ranges, C++26 -- Bartlomiej Filipek

By Blog Staff | Jun 5, 2025 05:01 PM | Tags: None

C++ continues to refine its range library, offering developers more efficient and expressive ways to manipulate collections. In this post, we'll dive into three powerful range adaptors—concat_view, join_view, and join_with_view—exploring their differences, use cases, and practical examples.

How to Join or Concat Ranges, C++26

by Bartlomiej Filipek

From the article:

Modern C++ continuously improves its range library to provide more expressive, flexible, and efficient ways to manipulate collections. Traditionally, achieving tasks like concatenation and flattening required manual loops, copying, or custom algorithms. With C++’s range adaptors, we now have an elegant and efficient way to process collections lazily without unnecessary allocations.

In this post, we will explore three powerful range adaptors introduced in different C++ standards:

std::ranges::concat_view (C++26)

std::ranges::join_view (C++20)

std::ranges::join_with_view (C++23)

Let’s break down their differences, use cases, and examples.

std::ranges::concat_view (C++26)

The concat_view allows you to concatenate multiple independent ranges into a single sequence. Unlike join_view, it does not require a range of ranges—it simply merges the given ranges sequentially while preserving their structure.

In short:

Takes multiple independent ranges as arguments.

Supports random access if all underlying ranges support it.

Allows modification if underlying ranges are writable.

Lazy evaluation: No additional memory allocations.

CppCon 2024 Rust Programming in 5 Minutes -- Tyler Weaver

By Blog Staff | Jun 4, 2025 12:56 PM | Tags: None

Lightning Talk: Rust Programming in 5 Minutes

by Tyler Weaver

Summary of the talk:

I'm now working in Rust and now I have time for all sorts of frivolous learning. It is glorious. I'm going to try in 5min to teach a bit of Rust to a C++ audience.

The call for talks for Meeting C++ 2025...

By Meeting C++ | Jun 4, 2025 11:03 AM | Tags: meetingcpp conference

While the official deadline is today, you can submit your talks until Sunday, as on Monday/Tuesday the voting starts.

The Meeting C++ 2025 call for talks deadline is today, but...

by Jens Weller

From the article:

Today is the official end of the call for Talks for Meeting C++ 2025. You can still edit and submit talks until the voting begins next week.

The Usual Arithmetic Confusions -- Shafik Yaghmour

By Blog Staff | Jun 3, 2025 05:01 PM | Tags: None

C++’s type conversion rules—particularly the usual arithmetic conversions and integral promotions—are often misunderstood, even by experienced developers. These rules quietly reshape operands behind the scenes during arithmetic and relational operations, sometimes leading to surprising or platform-dependent behavior that can be tricky to debug or reason about.

The Usual Arithmetic Confusions

by Shafik Yaghmour

From the article:

There are a lot of aspects of C++ that are not well understood and lead to all sorts of confusion. The usual arithmetic conversions and the integral promotions are two such aspects. Certain binary operators (arithmetic, relational and spaceship) require their operands to have a common type. The usual arithmetic conversions are the set of steps that gets operands to a common type. While the integral promotions brings integral types smaller than int and unsigned int to either int or unsigned int depending on which one can represent all the values of the source type. This is one of the areas in C++ that comes directly from C, so pretty much all of these examples applies to C as well as C++.

We will see some examples with results that many may find surprising. After seeing some of these cases we will discuss the rules and how they explain each case. While covering each rule we will present examples to clarify the rule. We will referring to ILP32 and LP64 data models and it may help to familiarize yourself with the size of types in these models.

It would also help to understand integer literals and the rules around what the type of an integer literal will be in various cases e.g.
// https://cppinsights.io/s/0ffee264 
void f() { 
    auto x1 = 1; // Integer literal 1 will have type int 
    auto x2 = 1U; // Integer literal 1L will have type unsigned int 
    auto x3 = 1L; // Integer literal 1L will have type long int 
    auto x4 = 1UL; // Integer literal 1UL will have type unsigned long int 
} 
I will be including C++ Insights links for many examples.

CppCon 2024 Introduction to Wait-free Algorithms in C++ Programming -- Daniel Anderson

By Blog Staff | Jun 2, 2025 12:49 PM | Tags: None

Introduction to Wait-free Algorithms in C++ Programming

by Daniel Anderson

Summary of the talk:

If you've attended any talks about concurrency, you've no doubt heard the term "lock-free programming" or "lock-free algorithms". Usually these talks will give you a slide that explains vaguely what this means, but you accept that is is approximately (but not quite exactly) equal to "just don't use locks". More formally, lock-freedom is about guaranteeing how much progress your algorithm will make in a given time. Specifically, a lock-free algorithm will always make some progress on at least one operation/thread. It does not guarantee however that all threads make progress. In a lock-free algorithm, a particular operation can still be blocked for an arbitrary long time because of the actions of other contending threads. What can we do in situations where this is unacceptable, such as when we want to guarantee low latency for every operation on our data structure rather than just low average latency?

In these situations, there is a stronger progress guarantee that we can aim for called wait-freedom. An algorithm is wait free if every operation is guaranteed to make progress in a bounded amount of time, i.e., no thread can ever be blocked for an arbitrarily long time. This helps to guarantee low tail latency for all operations, rather than low average latency in which some operations are left behind. In this talk, we will give an introduction to designing and implementing wait-free algorithms.

Without assuming too much background of the audience, we will review the core ideas of lock-free programming and understand the classic techniques for transforming a blocking algorithm into a lock-free one. The main bread-and-butter technique for lock-free algorithms is the compare-exchange loop or "CAS loop", in which an operation reads the current state of the data structure, creates some sort of updated version, and then attempts to install the update via a compare-exchange, looping until it succeeds. compare-exchange loops suffer under high contention since the success of one operation will often cause another to have to repeat work until they succeed. The bread-and-butter technique of wait-free programming that overcomes this issue is helping. When operations contend, instead of racing to see who wins, an operation that encounters another already-in-progress operation attempts to help it complete first, then proceeds with its own operation. This results in the initial operation succeeding instead of being clobbered and forced to try again.

CppCon 2024 Strategies for Developing Safety-Critical Software in C++ -- Emily Durie-Johnson

By Blog Staff | May 30, 2025 12:45 PM | Tags: None

Lightning Talk: Strategies for Developing Safety-Critical Software in C++

by Emily Durie-Johnson

Summary of the talk:

This talk delves into the importance of a safety-first mindset in software development within the medical device domain. It explores the intersection of C++ and industry standards that ensure safety-critical software. Attendees will learn to ask guiding questions during code development that emphasize the importance of coding as if the technology will be used on their loved ones. With real-world examples and best practices, this session highlights the personal and professional responsibilities of engineers in safety-critical fields to create reliable software.

Function overloading is more flexible than template function specialization -- Raymond Chen

By Blog Staff | May 29, 2025 05:00 PM | Tags: None

When trying to specialize a templated function for specific types, it’s easy to fall into subtle traps around how parameter types are matched. A colleague recently ran into this issue while attempting to specialize a function for a Widget and a string literal, only to be met with confusing compiler errors that hinted at deeper quirks in C++'s type deduction and function template specialization rules.

Function overloading is more flexible (and more convenient) than template function specialization

by Raymond Chen

From the article:

A colleague of mine was having trouble specializing a templated function. Here’s a simplified version.
template<typename T, typename U>
bool same_name(T const& t, U const& u)
{
    return t.name() == u.name();
}
They wanted to provide a specialization for the case that the parameters are a Widget and a string literal.
template<>
bool same_name<Widget, const char[]>(Widget const& widget, const char name[])
{
    return strcmp(widget.descriptor().name().c_str(), name) == 0;
}
However, this failed to compile:
// msvc
error C2912: explicit specialization 'bool 
same_name<Widget,const char[]>(const Widget &,const char 
[])' is not a specialization of a function template
What do you mean “not a specialization of a function template”? I mean doesn’t it look like a specialization of a function template? It sure follows the correct syntax for a function template specialization.

CppCon 2024 C++ Under the Hood: Internal Class Mechanisms -- Chris Ryan

By Blog Staff | May 28, 2025 12:41 PM | Tags: None

C++ Under the Hood: Internal Class Mechanisms

by Chris Ryan

Summary of the talk:

My talk will examine the internal C++ mechanisms around the topics of:

The C++ onion as it relates to construction, destruction and polymorphism,

Order of Object construction & destruction, and pre- & post-main() processing.

Member Function Pointers (not your father’s C function pointer),

Member Data Pointers (not raw pointers) (data-morphic functionality),

Understanding the Call Stack, Stack Frames and Base Pointer mechanisms.