朴素布尔否定

std::atomic_bool b;
b = !b;

似乎不是原子的。我怀疑这是因为 operator! 触发了对普通 bool 的转换。一个人将如何原子地执行等价的否定？下面的代码说明天真的否定不是原子的：

#include <thread>
#include <vector>
#include <atomic>
#include <iostream>
typedef std::atomic_bool Bool;
void flipAHundredThousandTimes(Bool& foo) {
  for (size_t i = 0; i < 100000; ++i) {
    foo = !foo;
// Launch nThreads std::threads. Each thread calls flipAHundredThousandTimes 
// on the same boolean
void launchThreads(Bool& foo, size_t nThreads) {
  std::vector<std::thread> threads;
  for (size_t i = 0; i < nThreads; ++i) {
    threads.emplace_back(flipAHundredThousandTimes, std::ref(foo));
  for (auto& thread : threads) thread.join();
int main() {
  std::cout << std::boolalpha;
  Bool foo{true};
  // launch and join 10 threads, 20 times.