Example of using mutex to control concurrent access to a queue

mutex_queue.cpp

#include <mutex>
#include <queue>

std::queue<int> q; // Queue which multiple threads might add/remove from
std::mutex m; // Mutex to protect this queue

void AddToQueue(int i)
{
    m.lock();
    q.push(i);
    m.unlock();
}

int RemoveFromQueue()
{
    int i = -1;
    m.lock();
    if (!q.empty())
    {
        i = q.front();
        q.pop();
    }
    m.unlock();
    return i;
}