Example of using lock_guard to control concurrent access to a queue

lock_guard_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)
{
    std::lock_guard<std::mutex> lg(m); // Lock will be held from here to end of function
    q.push(i);
}
 
int RemoveFromQueue()
{
    int i = -1;
    {
        std::lock_guard<std::mutex> lg(m); // Lock held from here to end of scope
        if (!q.empty())
        {
            i = q.front();
            q.pop();
        }
    }
    return i;
}