C++23 likes to move it! -- Sandor Dargo

By Blog Staff | Mar 1, 2024 12:50 PM | Tags: None

C++23 is going to bring us a few changes regarding move operations. It mostly means extended support in the standard library, but there is also one change directly in the language. Let’s start with that.

C++23 likes to move it!

by Sandor Dargo

From the article:

P2266R3 is a quite great proposal both in terms of its high-quality explanation and the amount of proposed changes in wording. I think if you’re interested in exploring a readable proposal, this might be the one.

Let me try to summarize it briefly.

Since the introduction of move semantics and rvalue references in C++11, we can return move-only types by value:

struct Widget {
    Widget(Widget&&);
};

Widget one(Widget w) {
    return w;
}

C++14 extended this support so that even converting constructors accepting an rvalue type can be called to invoke an implicit move.

struct RRefTaker {
    RRefTaker(Widget&&); // here is the converting constructor
};

RRefTaker two(Widget w) {
    return w;
}

As you can see, the two examples...

SObjectizer Tales – 21. Performance, part 2--Marco Arena

By Marco Arena | Feb 29, 2024 01:19 AM | Tags: sobjectizer intermediate c++20

A new episode of the series about SObjectizer and message passing:

SObjectizer Tales – 21. Performance, part 2

by Marco Arena

From the article:

In this episode we continue our exploration of performance considerations within the actor model, with a specific focus on measuring service time.

Parsing Numbers At Compile Time with C++17, C++23, and C++26 -- Bartlomiej Filipek

By Blog Staff | Feb 28, 2024 12:41 PM | Tags: None

Thanks to the powerful constexpr keyword and many enhancements in recent C++ standards, we can now perform a lot of computations at compile time. In this text, we’ll explore several techniques for parsing integers, including the “naive” approach, C++23,from_chars,std::optional, std::expected, and even some upcoming features in C++26.

Parsing Numbers At Compile Time with C++17, C++23, and C++26

by Bartlomiej Filipek

From the article:

Why at compile time?

While it may sound like a theoretical experiment, since C++11 we can shift more and more computations to compile-time. Here are some key areas and examples where constexpr can be beneficial:

• Building lookup tables
• Working with embedded resources (like fonts or bitmaps)
• Parsing configuration strings
• Regular Expressions at compile time
• Working with bit flags and bits
• UB program verification (constexpr context guarantees no UB in your code)
• and many more… see Your New Mental Model of constexpr - Jason Turner - CppCon 2021 - YouTube or Lightning Talk: Memoizing Constexpr Programs - Chris Philip - CppCon 2021 - YouTube or Anything can be a Constexpr if you try hard enough - Zoe Carver - CppCon 2019 - YouTube

Starting easy from C++17 

Starting with C++17, we are now capable of writing complex constexpr functions. However, our ability to do so is still limited by the range of algorithms available in that context. Luckily, with the introduction of string_view in that version of C++, there is no longer any need to work with “raw” const char* buffers.

Class Invariants -- Andrzej Krzemieński

By Blog Staff | Feb 26, 2024 10:55 AM | Tags: None

This article explores the concept of class invariants in C++ and their significance in maintaining code integrity and abstraction. It highlights the difference between struct and class definitions and discusses the role of class invariants in guaranteeing the correctness of class objects. The article also touches upon the trade-offs between strong and weak invariants and provides insights into when to define a new class with proper invariants.

Class Invariants

by Andrzej Krzemieński

From the article:

The primary motivation for defining a class in C++ is to reflect and maintain a class invariant. In this post we will see what class invariants are and how you deal with them. Class invariants are important part of C++, even though there is no “invariant” keyword in C++.

Contrast the following two class definitions:

struct Point
{
  int x;
  int y;
};

class Range
{
  int _min;
  int _max;

public:
  // ...
};

In C++ a struct is practically a class but with a different default member access. The first is an aggregate: it only allows two pieces of data to travel together. If it was not for the nice member names, we might have as well used std::pair<int, int> instead. 

SObjectizer Tales – 20. Performance, part 1--Marco Arena

By Marco Arena | Feb 22, 2024 01:18 AM | Tags: sobjectizer intermediate c++20

A new episode of the series about SObjectizer and message passing:

SObjectizer Tales – 20. Performance, part 1

by Marco Arena

From the article:

In this episode we embark on a three-part full-immersion on performance metrics and considerations in message-passing styled applications, with a specific emphasis on SObjectizer and the in-process actor model.

Optimizing the Unoptimizable: A Journey to Faster C++ Compile Times -- Victor Zverovich

By Blog Staff | Feb 20, 2024 10:49 AM | Tags: None

In this post, Victor talks about bringing compile times of the {fmt} library on par with the C standard I/O library (stdio).

Optimizing the Unoptimizable: A Journey to Faster C++ Compile Times

by Victor Zverovich

From the article:

First some background: {fmt} is a popular open-source formatting library for C++ that provides a better alternative to C++ iostreams and C stdio. It has already surpassed stdio in many areas:

• Type safety with compile-time format string checks available by default since C++20 and as an opt in for C++14/17. Runtime format strings are also safe to use in {fmt} which is impossible to achieve in printf.
• Extensibility: user-defined type can be made formattable and most standard library types such as containers, dates and times are formattable out of the box.
• Performance: {fmt} is significantly faster than common standard library implementations of printf, in some cases by an order of magnitude (e.g. on floating-point formatting).
• Portable Unicode support.

However, one area where stdio remained significantly better was compile times. 

Seastar, ScyllaDB, and C++23

By Jordi Mon Companys | Feb 17, 2024 05:36 AM | Tags: c++20 c++17

Seastar announces that now that C++23 is available, they will support C++23 and C++20 (dropping support for C++17) in accordance with their support policy

Seastar, ScyllaDB, and C++23

By Avi Kivity

From the article:

Seastar is an open-source (Apache 2.0 licensed) C++ framework for I/O intensive asynchronous computing, using the thread-per-core model. Seastar underpins several high- performance distributed systems: ScyllaDB, Redpanda, and Ceph Crimson. Seastar source is available on github. As a C++ framework, Seastar must choose which C++ versions to support. The support policy is last-two-versions. That means that at any given time, the most recently released version as well as the previous one are supported, but earlier versions cannot be expected to work. This policy gives users of the framework three years to upgrade to the next C++ edition while not constraining Seastar to ancient versions of the language.

Now that C++23 has been ratified, Seastar now officially supports C++20 and C++23. The previously supported C++17 is now no longer supported.

The Case of the Vector With an Impossibly Large Size -- Raymond Chen

By Blog Staff | Feb 16, 2024 10:46 AM | Tags: None

In this software troubleshooting case, a customer experienced program crashes, and a detailed analysis of the code revealed several issues. The primary problem stemmed from lazy initialization of a widget list, leading to inconsistent vector states and potential crashes. Additionally, a multithreading issue was identified, highlighting the importance of thread-safety mechanisms in code that can be accessed concurrently.

The Case of the Vector With an Impossibly Large Size

by Raymond Chen

From the article:

A customer had a program that crashed with this stack:

contoso!Widget::GetCost
contoso!StandardWidgets::get_TotalCost+0x12f
rpcrt4!Invoke+0x73
rpcrt4!Ndr64StubWorker+0xb9b
rpcrt4!NdrStubCall3+0xd7
combase!CStdStubBuffer_Invoke+0xdb
combase!ObjectMethodExceptionHandlingAction<<lambda_...> >+0x47
combase!DefaultStubInvoke+0x376
combase!ServerCall::ContextInvoke+0x6f3
combase!ComInvokeWithLockAndIPID+0xacb
combase!ThreadInvoke+0x103
rpcrt4!DispatchToStubInCNoAvrf+0x18
rpcrt4!RPC_INTERFACE::DispatchToStubWorker+0x1a9
rpcrt4!RPC_INTERFACE::DispatchToStubWithObject+0x1a7
rpcrt4!LRPC_SCALL::DispatchRequest+0x308
rpcrt4!LRPC_SCALL::HandleRequest+0xdcb
rpcrt4!LRPC_SASSOCIATION::HandleRequest+0x2c3
rpcrt4!LRPC_ADDRESS::HandleRequest+0x183
rpcrt4!LRPC_ADDRESS::ProcessIO+0x939
rpcrt4!LrpcIoComplete+0xff
ntdll!TppAlpcpExecuteCallback+0x14d
ntdll!TppWorkerThread+0x4b4
kernel32!BaseThreadInitThunk+0x18
ntdll!RtlUserThreadStart+0x21

They wondered if some recent change to Windows was the source of the problem, since it didn’t happen as much in earlier versions of Windows.

 

2024-02 Mailing Available

By Administrator | Feb 15, 2024 11:19 AM | Tags: None

The 2024-02 mailing of new standards papers is now available.

SObjectizer Tales – 19. Thread-safe handlers--Marco Arena

By Marco Arena | Feb 14, 2024 11:31 PM | Tags: sobjectizer intermediate c++20

A new episode of the series about SObjectizer and message passing:

SObjectizer Tales – 19. Thread-safe handlers

by Marco Arena

From the article:

In this episode we explore thread-safe message handlers and revisit the problem of distributing work across multiple threads.