C++C++11C++14C++17C++20Learn C++

How to Use Atomic_flag In Modern C++?

How to Use Atomic flag In Modern C++

C++11 allows the use of atomics in signal handlers. In C++17 the signal handler feature is further improved. The std::atomic_flag is an atomic boolean type that is guaranteed to be lock-free and can be used in signal handlers. Moreover, the <csignal> header in C++ has an integer type std::sig_atomic_t that can be accessed as an atomic entity even in the presence of asynchronous interrupts made by signals. In this post, we explain how to use atomic_flag in C++.

What is atomic_flag in C++?

The std::atomic_flag is a flag in the atomics library which is known as an atomic boolean type. The std::atomic is guaranteed to be lock-and does not provide load or store operations. In addition, they provide synchronization and order constraints on the program execution.

Here is the general syntax since C++11.

Here is how we can declare it.

What are the features of atomic_flag in modern C++?

The std::atomic_flag has useful features, these are as follows.

The clear() feature is used to set flags to false atomically, in example we can use it with a memory_order as below,

test_and_set() tests the flag to true and obtains its previous value, in example we can use it with a memory_order in a while loop as we show in the example below:

The test() feature is new in C++20, returns the value of the flag atomically, like so:

The wait() feature is new in C++20 and it blocks the thread until the atomic value changes and it is notified. Here is an example:

in C++20, there are notify_one() and notify_all() features too.

Note that, std::atomic_flag is a pretty low-level type – you can consider using atomic_bool instead. Also, you can use member functions with the set and the clear methods. You can also use higher level constructs, such as a std::mutex and std:: lock_guard.

How to use atomic_flag in modern C++?

Here is an atomic_flag C++ example.

The std::atomic_flag is an atomic boolean type that is guaranteed to be lock-free and can be used in signal handlers. If you want to use atomics in signal handlers see Allow atomics use in signal handlers Proposal document.

How to Use Atomic flag In Modern C++ C++ Builder logo

C++ Builder is the easiest and fastest C and C++ IDE for building simple or professional applications on the Windows, MacOS, iOS & Android operating systems. It is also easy for beginners to learn with its wide range of samples, tutorials, help files, and LSP support for code. RAD Studio’s C++ Builder version comes with the award-winning VCL framework for high-performance native Windows apps and the powerful FireMonkey (FMX) framework for cross-platform UIs.

There is a free C++ Builder Community Edition for students, beginners, and startups; it can be downloaded from here. For professional developers, there are Professional, Architect, or Enterprise version.

Oh hi there 👋
It’s nice to meet you.

Sign up to receive awesome C++ content in your inbox, every day.

We don’t spam! Read our privacy policy for more info.

About author

Dr. Yilmaz Yoru has 35+ years of coding with more than 30+ programming languages, mostly C++ on Windows, Android, Mac-OS, iOS, Linux, and some other operating systems. He graduated and received his MSc and PhD degrees from the Department of Mechanical Engineering of Eskisehir Osmangazi University. He is the founder and CEO of ESENJA LLC Company. His interests are Programming, Thermodynamics, Fluid Mechanics, Artificial Intelligence, 2D & 3D Designs, and high-end innovations.
Related posts
C++C++11C++14C++17C++20Introduction to C++Learn C++Syntax

Learn Default Constructors Of Classes In Modern C++

Artificial Intelligence TechC++C++11C++14C++17Learn C++

How To Develop Special AI Activation Functions In C++?

Artificial Intelligence TechC++C++11C++14C++17Language FeatureLearn C++

Learn How To Read The WAV Waveform Audio File Format In C++

C++C++11Learn C++

What Is Assignment Operator Overloading?