Book Image

Concurrency with Modern C++

By : Rainer Grimm
Book Image

Concurrency with Modern C++

By: Rainer Grimm

Overview of this book

C++11 is the first C++ standard that deals with concurrency. The story goes on with C++17 and will continue with C++20/23. Concurrency with Modern C++ is a practical guide that gets you to grips with concurrent programming in Modern C++. Starting with the C++ memory model and using many ready-to-run code examples, the book covers everything you need to improve your C++ multithreading skills. You'll gain insight into different design patterns. You'll also uncover the general consideration you have to keep in mind while designing a concurrent data structure. The final chapter in the book talks extensively about the common pitfalls of concurrent programming and ways to overcome these hurdles. By the end of the book, you'll have the skills to build your own concurrent programs and enhance your knowledge base.
Table of Contents (19 chapters)
Free Chapter
1
Reader Testimonials
19
Index

ABA Problem

ABA means you read a value twice and each time it returns the same value A. Therefore you conclude that nothing changed in between. However, you missed the fact that the value was updated to B somewhere in between.

Let me first use a simple scenario to introduce the problem.

An Analogy

The scenario consists of you sitting in a car and waiting for the traffic light to become green. Green stands in our case for B, and red for A. What’s happening?

  1. You look at the traffic light, and it is red (A).
  2. Because you are bored, you begin to check the news on your smartphone and forget the time.
  3. You look once more at the traffic light. Damn, it is still red (A).

Of course, the traffic light became green (B) between your two checks. Therefore, what seems to be one red phase was a full cycle.

What does this mean for threads (processes)? Now more formally.

  1. Thread 1 reads the variable var with value A.
  2. Thread 1 is preempted, and thread 2 runs.
  3. Thread 2 changes...