[Multithreading, VC++] Problem z zakleszczaniem

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

class barrier {
public:
    explicit barrier( unsigned int thread_count );
   
    void wait();
private:
    const unsigned int thread_count;
    unsigned waiting_thread_count;
    bool flag;
    std::mutex mutex;
    std::condition_variable condvar;
};

barrier::barrier( unsigned int thread_count )
    : thread_count( thread_count )
     , waiting_thread_count( 0 )
     , flag( false )
{
}

void barrier::wait()
{
    std::unique_lock < std::mutex > guard( mutex );
    const bool expected = !flag;
    ++waiting_thread_count;
    if( waiting_thread_count == thread_count ) {
        waiting_thread_count = 0;
        flag = expected;
        condvar.notify_all();
    } else {
        condvar.wait( guard,[ & ] { return flag == expected; } );
    }
}

int main()
{
    std::vector < std::thread > threads;
    barrier bar( 10 );
    std::mutex m;
    for( int i = 0; i < 10; ++i ) {
        threads.emplace_back([ &, i ]() {
            {
                const std::lock_guard < std::mutex > guard( m );
                std::cout << "Worker " << i << " before barrier\n" << std::flush;
            }
            bar.wait();
            {
                const std::lock_guard < std::mutex > guard( m );
                std::cout << "Worker " << i << " after barrier\n" << std::flush;
            }
        } );
    }
   
    for( auto & thread: threads ) {
        thread.join();
    }
}