蓝桥ROS机器人之现代C++学习笔记7.5 原子操作

Posted 2022-04-28 zhangrelay

学习如下代码：

线程竞争和乱序执行

#include <thread>
#include <iostream>

int main() 
    int a = 0;
    volatile int flag = 0;

    std::thread t1([&]() 
        while (flag != 1);

        int b = a;
        std::cout << "b = " << b << std::endl;
    );

    std::thread t2([&]() 
        a = 5;
        flag = 1;
    );

    t1.join();
    t2.join();
    return 0;

---

#include <iostream>       // std::cout
#include <atomic>         // std::atomic, std::memory_order_relaxed
#include <thread>         // std::thread

std::atomic_int foo (0);

void set_foo(int x) 
  foo.store(x,std::memory_order_relaxed);     // set value atomically


void print_foo() 
  int x;
  do 
    x = foo.load(std::memory_order_relaxed);  // get value atomically
   while (x==0);
  std::cout << "foo: " << x << '\\n';


int main ()

  std::thread first (print_foo);
  std::thread second (set_foo,10);
  first.join();
  //second.join();
  return 0;

---

#include <atomic>
#include <thread>
#include <iostream>

std::atomic<int> count = 0;

int main() 
    std::thread t1([]()
        count.fetch_add(1);
    );
    std::thread t2([]()
        count++;        // identical to fetch_add
        count += 1;     // identical to fetch_add
    );
    t1.join();
    t2.join();
    std::cout << count << std::endl;
    return 0;

 

---

#include <atomic>
#include <iostream>

struct A 
    float x;
    int y;
    long long z;
;

int main() 
    std::atomic<A> a;
    std::cout << std::boolalpha << a.is_lock_free() << std::endl;
    return 0;

clang++ -std=c++2a

g++ -std=c++20

---

 

 

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