How Can I Create and Use a Thread Pool with Boost in C ?

boost::asio::io_service ioService;
boost::thread_group threadpool;

threadpool.create_thread(
    boost::bind(&boost::asio::io_service::run, &ioService)
);

ioService.post(boost::bind(myTask, "Hello World!"));

ioService.stop();

threadpool.join_all();

// Create io_service and thread_group
boost::asio::io_service ioService;
boost::thread_group threadpool;

// Start the ioService processing loop
boost::asio::io_service::work work(ioService);

// Add threads to the thread pool
threadpool.create_thread(
    boost::bind(&boost::asio::io_service::run, &ioService)
);
threadpool.create_thread(
    boost::bind(&boost::asio::io_service::run, &ioService)
);

// Assign tasks to the thread pool
ioService.post(boost::bind(myTask, "Hello World!"));
ioService.post(boost::bind(clearCache, "./cache"));
ioService.post(boost::bind(getSocialUpdates, "twitter,gmail,facebook,tumblr,reddit"));

// Stop the ioService processing loop
ioService.stop();

// Join all threads in the thread pool
threadpool.join_all();