#include <boost/thread/recursive_mutex.hpp>

#include <boost/thread/thread.hpp>

#include <iostream>

class counter

{

public:

counter() : count(0) { }

int add(int val)

{

boost::recursive_mutex::scoped_lock scoped_lock(mutex);

count += val;

return count;

}

int increment()

{

boost::recursive_mutex::scoped_lock scoped_lock(mutex);

return add(1);

}

private:

boost::recursive_mutex mutex;

int count;

};

counter c;

void change_count()

{

std::cout << "count == " << c.increment() << std::endl;

}

int main(int, char*[])

{

const int num_threads=4;

boost::thread_group threads;

for (int i=0; i < num_threads; ++i)

threads.create_thread(&change_count);

threads.join_all();

return 0;

}