An example of a simple queue class with internal locking for a blog post.

LockingQueue.cpp

#include <deque>
#include <mutex>
#include <cassert>

template<typename T, typename MutexType = std::mutex>
class queue
{
public:
    void enqueue(T value) {
        std::lock_guard<MutexType> guard(mutex_);
        q_.push_back(value);
    }
private:
    std::deque<T> q_;
    MutexType mutex_;

};

class mock_mutex {
public:
    void lock() {
        lock_called_ = true;
    }

    void unlock() {}

    bool was_locked() {
        return lock_called_;
    }
private:
    static bool lock_called_;
};

bool mock_mutex::lock_called_ = false;

int main() {
    mock_mutex mutex_tracker;
    queue<int, mock_mutex> subject;
    subject.enqueue(42);
    assert(mutex_tracker.was_locked());

    return 0;
}