search
HomeBackend DevelopmentC++Are C 11 Thread-Local Variables Considered Static by Default?

Are C  11 Thread-Local Variables Considered Static by Default?

Are Thread-Local Variables in C 11 Automatically Static?

In the context of thread safety and code organization, thread-local variables have gained prominence in C 11. These variables provide per-thread storage, ensuring that different threads operating on the same code have access to unique instances of the variable.

When defining a thread-local variable, it's essential to understand its implications and possible equivalence to static variables. This distinction can be particularly relevant when migrating existing code from a single-threaded to a multithreaded environment.

,Is There a Difference?

The C 11 Standard clarifies this question: "When thread_local is applied to a variable of block scope, the storage-class-specifier static is implied if it does not appear explicitly." This means that the following two code segments are equivalent:

<code class="cpp">void f() {
    thread_local vector<int> V;
    V.clear();
    ... // use V as a temporary variable
}</int></code>
<code class="cpp">void f() {
    static thread_local vector<int> V;
    V.clear();
    ... // use V as a temporary variable
}</int></code>

However, it's crucial to note that thread-local variables are distinct from static variables:

  • static variables have static storage duration, meaning they exist for the entire lifetime of the program.
  • thread_local variables have thread storage duration, meaning they exist only within the thread in which they are created.

This distinction is significant because thread-local variables ensure that each thread has its own instance of the variable, preventing conflicts between threads. Static variables, on the other hand, are shared among all threads.

Implications for Code Migration

When migrating code from a single-threaded to a multithreaded environment, it's essential to replace static variables with thread-local variables to avoid potential conflicts and ensure data consistency.

In the case of the code snippet provided, the original STATIC vector V can be safely replaced with thread_local vector V, as the code logic relies on a per-thread instance of the vector for intermediate values.

Summary

In C 11, thread_local variables are not automatically static, but the storage-class-specifier static is implied when thread_local is applied to a block-scoped variable. However, thread-local variables have a distinct thread storage duration, which is different from the static storage duration of static variables. When migrating code to a multithreaded environment, it's crucial to replace static variables with thread-local variables to ensure data consistency and avoid conflicts between threads.

The above is the detailed content of Are C 11 Thread-Local Variables Considered Static by Default?. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
From XML to C  : Data Transformation and ManipulationFrom XML to C : Data Transformation and ManipulationApr 16, 2025 am 12:08 AM

Converting from XML to C and performing data operations can be achieved through the following steps: 1) parsing XML files using tinyxml2 library, 2) mapping data into C's data structure, 3) using C standard library such as std::vector for data operations. Through these steps, data converted from XML can be processed and manipulated efficiently.

C# vs. C  : Memory Management and Garbage CollectionC# vs. C : Memory Management and Garbage CollectionApr 15, 2025 am 12:16 AM

C# uses automatic garbage collection mechanism, while C uses manual memory management. 1. C#'s garbage collector automatically manages memory to reduce the risk of memory leakage, but may lead to performance degradation. 2.C provides flexible memory control, suitable for applications that require fine management, but should be handled with caution to avoid memory leakage.

Beyond the Hype: Assessing the Relevance of C   TodayBeyond the Hype: Assessing the Relevance of C TodayApr 14, 2025 am 12:01 AM

C still has important relevance in modern programming. 1) High performance and direct hardware operation capabilities make it the first choice in the fields of game development, embedded systems and high-performance computing. 2) Rich programming paradigms and modern features such as smart pointers and template programming enhance its flexibility and efficiency. Although the learning curve is steep, its powerful capabilities make it still important in today's programming ecosystem.

The C   Community: Resources, Support, and DevelopmentThe C Community: Resources, Support, and DevelopmentApr 13, 2025 am 12:01 AM

C Learners and developers can get resources and support from StackOverflow, Reddit's r/cpp community, Coursera and edX courses, open source projects on GitHub, professional consulting services, and CppCon. 1. StackOverflow provides answers to technical questions; 2. Reddit's r/cpp community shares the latest news; 3. Coursera and edX provide formal C courses; 4. Open source projects on GitHub such as LLVM and Boost improve skills; 5. Professional consulting services such as JetBrains and Perforce provide technical support; 6. CppCon and other conferences help careers

C# vs. C  : Where Each Language ExcelsC# vs. C : Where Each Language ExcelsApr 12, 2025 am 12:08 AM

C# is suitable for projects that require high development efficiency and cross-platform support, while C is suitable for applications that require high performance and underlying control. 1) C# simplifies development, provides garbage collection and rich class libraries, suitable for enterprise-level applications. 2)C allows direct memory operation, suitable for game development and high-performance computing.

The Continued Use of C  : Reasons for Its EnduranceThe Continued Use of C : Reasons for Its EnduranceApr 11, 2025 am 12:02 AM

C Reasons for continuous use include its high performance, wide application and evolving characteristics. 1) High-efficiency performance: C performs excellently in system programming and high-performance computing by directly manipulating memory and hardware. 2) Widely used: shine in the fields of game development, embedded systems, etc. 3) Continuous evolution: Since its release in 1983, C has continued to add new features to maintain its competitiveness.

The Future of C   and XML: Emerging Trends and TechnologiesThe Future of C and XML: Emerging Trends and TechnologiesApr 10, 2025 am 09:28 AM

The future development trends of C and XML are: 1) C will introduce new features such as modules, concepts and coroutines through the C 20 and C 23 standards to improve programming efficiency and security; 2) XML will continue to occupy an important position in data exchange and configuration files, but will face the challenges of JSON and YAML, and will develop in a more concise and easy-to-parse direction, such as the improvements of XMLSchema1.1 and XPath3.1.

Modern C   Design Patterns: Building Scalable and Maintainable SoftwareModern C Design Patterns: Building Scalable and Maintainable SoftwareApr 09, 2025 am 12:06 AM

The modern C design model uses new features of C 11 and beyond to help build more flexible and efficient software. 1) Use lambda expressions and std::function to simplify observer pattern. 2) Optimize performance through mobile semantics and perfect forwarding. 3) Intelligent pointers ensure type safety and resource management.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. How to Fix Audio if You Can't Hear Anyone
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Chat Commands and How to Use Them
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

Safe Exam Browser

Safe Exam Browser

Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool