source: downloads/boost_1_33_1/libs/thread/tutorial/counter.cpp @ 20

// Copyright (C) 2001-2003
// William E. Kempf
//
// Permission to use, copy, modify, distribute and sell this software
// and its documentation for any purpose is hereby granted without fee,
// provided that the above copyright notice appear in all copies and
// that both that copyright notice and this permission notice appear
// in supporting documentation.  William E. Kempf makes no representations
// about the suitability of this software for any purpose.
// It is provided "as is" without express or implied warranty.

#include <boost/thread/mutex.hpp>
#include <boost/thread/thread.hpp>
#include <iostream>

boost::mutex mutex;
int counter=0;

void change_count()
{
    boost::mutex::scoped_lock lock(mutex);
    int i = ++counter;
    std::cout << "count == " << i << std::endl;
}

int main()
{
    const int num_threads = 4;
    boost::thread_group thrds;
    for (int i=0; i < num_threads; ++i)
        thrds.create_thread(&change_count);
    thrds.join_all();
}