c++11 std::atomic 原子操作

The main characteristic of atomic objects is that access to this contained value from different threads cannot cause data races。

提供对基本内建数据的互斥访问。

// atomic::exchange example
#include <iostream>       // std::cout
#include <atomic>         // std::atomic
#include <thread>         // std::thread
#include <vector>         // std::vector

std::atomic<bool> ready (false);
std::atomic<bool> winner (false);

void count1m (int id) {
  while (!ready) {}                  // wait for the ready signal
  
　for (int i=0; i<1000000; ++i) 
  {}   // go!, count to 1 million
  
　if (!winner.exchange(true)) 
　{ 
　　std::cout << "thread #" << id << " won!
"; 、
  }
};

int main ()
{
  std::vector<std::thread> threads;
  std::cout << "spawning 10 threads that count to 1 million...
";
  for (int i=1; i<=10; ++i) threads.push_back(std::thread(count1m,i));
  ready = true;
  for (auto& th : threads) th.join();

  return 0;
}