Why is std::atomic much slower than volatile bool?

Question

I\'ve been using volatile bool for years for thread execution control and it worked fine

// in my class declaration
volatile bool stop_;

-----------------

// I         


        

Answer 1

Since I'm curious about this, I tested it myself on Ubuntu 12.04, AMD 2.3 GHz, gcc 4.6.3.

#if 1
#include 
std::atomic stop_(false);
#else
volatile bool stop_ = false;
#endif

int main(int argc, char **argv)
{
    long n = 1000000000;
    while (!stop_) {
        if (--n < 0)
            stop_ = true;
    }

    return 0;
}

Compiled with g++ -g -std=c++0x -O3 a.cpp

Although, same conclusion as @aleguna:

• just bool:

  real 0m0.004s
  user 0m0.000s
  sys 0m0.004s

• volatile bool:

  $ time ./a.out
  real 0m1.413s
  user 0m1.368s
  sys 0m0.008s

• std::atomic:

  $ time ./a.out
  real 0m32.550s
  user 0m32.466s
  sys 0m0.008s

• std::atomic:

  $ time ./a.out
  real 0m32.091s
  user 0m31.958s
  sys 0m0.012s