C++ std::atomic_flag 实现spinLock

A spinlock mutex can be implemented in userspace using an atomic_flag.

一旦标识对象初始化完成,只能做三种操作:销毁、清除或设置并查询其先前的值。

这些分别对应析构函数、clear()函数以及test_and_set()函数。

clear和test_and_set操作都可以指定一个内存顺序,

clear是清除操作(atomically sets flag to false),

test_and_set是读改写操作(atomically sets the flag to true and obtains its previous value)

c++20 引入了 test 操作,即读数据操作(atomically returns the value of the flag)

 

 1 #include <thread>
 2 #include <vector>
 3 #include <iostream>
 4 #include <atomic>
 5 
 6 inline void cpu_relax() {
 7 #if defined(__aarch64__)
 8     asm volatile("yield" ::: "memory");
 9 #else
10     asm volatile("rep; nop" ::: "memory");
11 #endif
12 }
13 
14 std::atomic_flag lock = ATOMIC_FLAG_INIT;
15 
16 void f(int n)
17 {
18     for (int cnt = 0; cnt < 100; ++cnt) {
19         while (lock.test_and_set(std::memory_order_acquire))  // acquire lock
20              cpu_relax(); // spin
21         std::cout << "Output from thread " << n << '\n';
22         lock.clear(std::memory_order_release);               // release lock
23     }
24 }
25 
26 int main()
27 {
28     std::vector<std::thread> v;
29     for (int n = 0; n < 10; ++n) {
30         v.emplace_back(f, n);
31     }
32     for (auto& t : v) {
33         t.join();
34     }
35 }

 

posted @ 2021-01-21 09:55  Ray.floyd  阅读(154)  评论(0编辑  收藏  举报