What is the use of atomics in C++ multi-threaded programming?

atomics is used in multi-threaded programming to perform atomic operations to ensure the atomicity and visibility of shared data. The atomic library provides atomic variable types, such as std::atomic, and provides the following atomic operations: load, store, compare_exchange_strong. In the actual case, the atomic counter counter is updated simultaneously by multiple threads, and the fetch_add atomic operation ensures that the counter value remains consistent and prevents data competition. atomics ensure the safety and reliability of data shared by multi-threaded programs.

C The purpose of atomics in multi-threaded programming

In multi-threaded programming, atomics are used to execute on shared data Special variable type for atomic operations. Atomic operations ensure that data remains consistent even if multiple threads access it simultaneously.

Characteristics of atomic operations:

• Atomicity: The operation will be executed as an indivisible whole and will not be executed by other threads Interrupt.
• Visibility: Atomic operations on one thread are immediately visible to other threads.
• Ordering: Atomic operations on the same variable will be executed in order.

atomics library:

The <atomic> library in C provides atomic variable types, such as std: :atomic<int>, std::atomic<bool>, etc. These types provide the following built-in atomic operations:

• load(memory_order): Reads a value from a variable.
• store(value, memory_order): Store the value into a variable.
• compare_exchange_strong(expected, desired, memory_order): If the value of the variable is the same as expected, replace it with desired.

Practical case:

Suppose we have a shared counter that multiple threads update at the same time:

#include <thread>
#include <atomic>

std::atomic<int> counter;

void increment_counter() {
    // 使用原子操作累加计数器
    counter.fetch_add(1, std::memory_order_relaxed);
}

int main() {
    std::vector<std::thread> threads;

    // 创建并启动 10 个线程同时累加计数器
    for (int i = 0; i < 10; i++) {
        threads.emplace_back(increment_counter);
    }

    // 等待所有线程结束
    for (auto &thread : threads) {
        thread.join();
    }

    // 打印最终计数结果
    std::cout << "最终计数：" << counter << std::endl;
}

In this example, std::atomic<int> counter Variables are shared between multiple threads. increment_counter The function uses atomic operations fetch_add to accumulate the counter, ensuring that the counter value remains consistent even if threads execute simultaneously.

Using atomics can ensure that the shared data of multi-threaded programs is safe and reliable.

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