NOISSUE mark used accounts/sessions in selection menus

api/logic/Usable.h

@@ -0,0 +1,58 @@
+#pragma once
+
+#include <cstddef>
+#include <memory>
+
+class Usable;
+
+/**
+ * Base class for things that can be used by multiple other things and we want to track the use count.
+ *
+ * @see UseLock
+ */
+class Usable
+{
+	friend class UseLock;
+public:
+	std::size_t useCount()
+	{
+		return m_useCount;
+	}
+	bool isInUse()
+	{
+		return m_useCount > 0;
+	}
+protected:
+	virtual void decrementUses()
+	{
+		m_useCount--;
+	}
+	virtual void incrementUses()
+	{
+		m_useCount++;
+	}
+private:
+	std::size_t m_useCount = 0;
+};
+
+/**
+ * Lock class to use for keeping track of uses of other things derived from Usable
+ *
+ * @see Usable
+ */
+class UseLock
+{
+public:
+	UseLock(std::shared_ptr<Usable> usable)
+		: m_usable(usable)
+	{
+		// this doesn't use shared pointer use count, because that wouldn't be correct. this count is separate.
+		m_usable->incrementUses();
+	}
+	~UseLock()
+	{
+		m_usable->decrementUses();
+	}
+private:
+	std::shared_ptr<Usable> m_usable;
+};