ClickHouse/base/poco/Foundation/include/Poco/SingletonHolder.h

//
// SingletonHolder.h
//
// Library: Foundation
// Package: Core
// Module:  SingletonHolder
//
// Definition of the SingletonHolder template.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_SingletonHolder_INCLUDED
#define Foundation_SingletonHolder_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/Mutex.h"


namespace Poco
{


template <class S>
class SingletonHolder
/// This is a helper template class for managing
/// singleton objects allocated on the heap.
/// The class ensures proper deletion (including
/// calling of the destructor) of singleton objects
/// when the application that created them terminates.
{
public:
    SingletonHolder() : _pS(0)
    /// Creates the SingletonHolder.
    {
    }

    ~SingletonHolder()
    /// Destroys the SingletonHolder and the singleton
    /// object that it holds.
    {
        delete _pS;
    }

    S * get()
    /// Returns a pointer to the singleton object
    /// hold by the SingletonHolder. The first call
    /// to get will create the singleton.
    {
        FastMutex::ScopedLock lock(_m);
        if (!_pS)
            _pS = new S;
        return _pS;
    }

    void reset()
    /// Deletes the singleton object.
    {
        FastMutex::ScopedLock lock(_m);
        delete _pS;
        _pS = 0;
    }

private:
    S * _pS;
    FastMutex _m;
};


} // namespace Poco


#endif // Foundation_SingletonHolder_INCLUDED