qx-threadsafesingleton.h

#ifndef QX_THREAD_SAFE_SINGLETON_H
#define QX_THREAD_SAFE_SINGLETON_H
 
// Qt Includes
#include <QMutex>
#include <QRecursiveMutex>
 
// Intra-component Includes
#include "qx/core/qx-exclusiveaccess.h"
 
// Extra-component Includes
#include "qx/utility/qx-concepts.h"
 
namespace Qx
{
 
template<class Singleton, typename Mutex = QMutex>
    requires any_of<Mutex, QMutex, QRecursiveMutex>
class ThreadSafeSingleton
{
//-Class Members---------------------------------------------------------------------------------------------
private:
    // Needs to be static so it can be locked before the the singleton is created, or else a race in instance() could occur.
    static inline constinit Mutex smMutex;
 
//-Constructor----------------------------------------------------------------------------------------------
protected:
    ThreadSafeSingleton() = default;
 
//-Class Functions----------------------------------------------------------------------------------------------
public:
    static Qx::ExclusiveAccess<Singleton, QMutex> instance()
    {
        static Singleton s;
        return Qx::ExclusiveAccess(&s, &smMutex); // Provides locked access to singleton, that unlocks when destroyed
    }
};
 
}
 
//-Macros----------------------------------------------------------------------------------------------------------
// Macro to be used in all derivatives
#define QX_THREAD_SAFE_SINGLETON(...) friend ThreadSafeSingleton<__VA_ARGS__>
 
#endif // QX_THREAD_SAFE_SINGLETON_H