Move source files for ThreadSafeQueue to correct directories

lib/ThreadSafeQueue/src/ThreadSafeQueue.h

@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#pragma once
+
+#include <mutex>
+#include <optional>
+#include <queue>
+
+template <typename T>
+class ThreadSafeQueue {
+public:
+    ThreadSafeQueue() = default;
+    ThreadSafeQueue(const ThreadSafeQueue<T>&) = delete;
+    ThreadSafeQueue& operator=(const ThreadSafeQueue<T>&) = delete;
+
+    ThreadSafeQueue(ThreadSafeQueue<T>&& other)
+    {
+        std::lock_guard<std::mutex> lock(_mutex);
+        _queue = std::move(other._queue);
+    }
+
+    virtual ~ThreadSafeQueue() { }
+
+    unsigned long size() const
+    {
+        std::lock_guard<std::mutex> lock(_mutex);
+        return _queue.size();
+    }
+
+    std::optional<T> pop()
+    {
+        std::lock_guard<std::mutex> lock(_mutex);
+        if (_queue.empty()) {
+            return {};
+        }
+        T tmp = _queue.front();
+        _queue.pop();
+        return tmp;
+    }
+
+    void push(const T& item)
+    {
+        std::lock_guard<std::mutex> lock(_mutex);
+        _queue.push(item);
+    }
+
+    T front()
+    {
+        std::lock_guard<std::mutex> lock(_mutex);
+        return _queue.front();
+    }
+
+private:
+    // Moved out of public interface to prevent races between this
+    // and pop().
+    bool empty() const
+    {
+        return _queue.empty();
+    }
+
+    std::queue<T> _queue;
+    mutable std::mutex _mutex;
+};