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Modern C++ Programming Cookbook

You're reading from   Modern C++ Programming Cookbook Master Modern C++ with comprehensive solutions for C++23 and all previous standards

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Product type Paperback
Published in Feb 2024
Publisher Packt
ISBN-13 9781835080542
Length 816 pages
Edition 3rd Edition
Languages
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Author (1):
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Marius Bancila Marius Bancila
Author Profile Icon Marius Bancila
Marius Bancila
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Toc

Table of Contents (15) Chapters Close

Preface 1. Learning Modern Core Language Features 2. Working with Numbers and Strings FREE CHAPTER 3. Exploring Functions 4. Preprocessing and Compilation 5. Standard Library Containers, Algorithms, and Iterators 6. General-Purpose Utilities 7. Working with Files and Streams 8. Leveraging Threading and Concurrency 9. Robustness and Performance 10. Implementing Patterns and Idioms 11. Exploring Testing Frameworks 12. C++ 20 Core Features 13. Other Books You May Enjoy
14. Index

Using promises and futures to return values from threads

In the first recipe of this chapter, we discussed how to work with threads. You also learned that thread functions cannot return values and that threads should use other means, such as shared data, to do so; however, for this, synchronization is required. An alternative to communicating a return value or an exception with either the main or another thread is using std::promise. This recipe will explain how this mechanism works.

Getting ready

The promise and future classes used in this recipe are available in the std namespace in the <future> header.

How to do it...

To communicate a value from one thread to another through promises and futures, do this:

  1. Make a promise available to the thread function through a parameter; for example:
    void produce_value(std::promise<int>& p)
    {
      // simulate long running operation
      {
        using namespace std::chrono_literals;
        std::this_thread...
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