C ++ Mutex能否保证避免竞争条件?

时间:2015-09-13 18:19:57

标签: c++ multithreading

我正在编写一个简单的例子来测试C ++ Threads和Mutexes:

#include <iostream>
#include <vector>
#include <thread>
#include <mutex>

const int num_th = 50;
const int num_vals = 20;
const int num_it = 1000;

class MyVector {
 public:
  MyVector(int size): vals_(size, 0), idx_(0), mtx_() {}

  void inc() 
  {
    mtx_.lock();
    for(int i=0; i<num_it; i++)
    {
       vals_[idx_]++;
       idx_= (idx_+1) % num_vals;
    }
    mtx_.unlock();
  }

  int getVal(int idx) {return vals_[idx];}

private:
  std::mutex mtx_;
  int idx_;
  std::vector<int> vals_;
};


int main(int argc, char *argv[])
{
  MyVector m(num_vals);

  std::thread t1[num_th];
  for(int i=0; i<num_th; i++)
     t1[i] = std::thread(&MyVector::inc, &m);

  for(int i=0; i<num_th;i++)
     t1[i].join();

  for(int i=0; i<num_vals; i++)
    std::cout<<" "<<m.getVal(i);

  return 0;
}

执行后,所有值应该相同,但这是输出:

 2053 2063 2054 2038 2029 2038 2036 2043 2048 2049 2048 2055 2055 2050 2050 2051 2051 2055 2042 2066

C ++ Mutexs真的能保证相互排斥,还是我错过了什么?

0 个答案:

没有答案