With the relaxed semantics, we have no synchronizations and ordering constraints on atomic operations.
With the relaxed semantics, only the atomicity of the operations on atomics is left.
std::cout << y.load(std::memory_order_relaxed) << " ";
std::cout << x.load(std::memory_order_relaxed) << std::endl;
Now, the questions are very easy to answer. Does the program have well-defined behavior? Which values for x and y are possible? On the one hand, all operations on x and y are atomic. So the program is well-defined. On the other hand, there are no restrictions on the interleaving of the threads. In the end, thread two can see the operations on thread 1 in a different order. So this is the first time in our process of ongoing optimizations that thread two can display x == 0 and y == 1. All combinations of x and y are possible.
I'm curious, what the graph of CppMem will look like for x == 0 and y == 1?
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atomic_int x= 0;
atomic_int y= 0;
That was the CppMem program. Now to the graph.
Execution for (y=0,x=2000)
The graph shows crystal clear unintuitive behavior.
x reads the value 2000 from the writing thread, but y reads 0 from the main thread. What happens when the reading of y is sequenced before the reading of x? Sequenced before exact means that the operation e:Rrix sb is sequenced-before the operation f:Rrix.
This was the last post in my mini-series about ongoing optimization. So, what's next? There are a lot of issues with the singleton pattern. I'm aware of that. But the singleton pattern is an ideal use case for a variable, which has to be initialized in a thread-safe way. From that point on, you can use it without synchronization.
So in the next post, I discuss different ways to initialize a singleton in a multithreading environment. You get the performance numbers and can reason about your use cases for the thread-safe initialization of a variable.
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Standard Seminars (English/German)
Here is a compilation of my standard seminars. These seminars are only meant to give you a first orientation.
- C++ - The Core Language
- C++ - The Standard Library
- C++ - Compact
- C++11 and C++14
- Concurrency with Modern C++
- Design Pattern and Architectural Pattern with C++
- Embedded Programming with Modern C++
- Generic Programming (Templates) with C++
- Clean Code with Modern C++
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suggesting that I actually enjoyed the usual info a person provide on your guests?
Is gonna be back continuously in order to inspect new posts
And he just bought me lunch since I found it for him smile So
let me rephrase that: Thank you for lunch!