singleton.h

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/***************************************************************************
 * include/stxxl/bits/singleton.h
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2008, 2011 Andreas Beckmann <[email protected]>
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#ifndef STXXL_SINGLETON_HEADER
#define STXXL_SINGLETON_HEADER

#include <cstdlib>

#include <stxxl/types>
#include <stxxl/bits/noncopyable.h>
#include <stxxl/bits/common/mutex.h>
#include <stxxl/bits/common/exithandler.h>


STXXL_BEGIN_NAMESPACE

template <typename INSTANCE, bool destroy_on_exit = true>
class singleton : private noncopyable
{
 typedef INSTANCE instance_type;
 typedef instance_type* instance_pointer;
 typedef volatile instance_pointer volatile_instance_pointer;

 static volatile_instance_pointer instance;

 static instance_pointer create_instance();
 static void destroy_instance();

public:
 inline static instance_pointer get_instance()
 {
 if (!instance)
 return create_instance();

 return instance;
 }
};

template <typename INSTANCE, bool destroy_on_exit>
typename singleton<INSTANCE, destroy_on_exit>::instance_pointer
singleton<INSTANCE, destroy_on_exit>::create_instance()
{
 static mutex create_mutex;
 scoped_mutex_lock instance_write_lock(create_mutex);
 if (!instance) {
 instance = new instance_type();
 if (destroy_on_exit)
 register_exit_handler(destroy_instance);
 }
 return instance;
}

template <typename INSTANCE, bool destroy_on_exit>
void singleton<INSTANCE, destroy_on_exit>::destroy_instance()
{
 instance_pointer inst = instance;
 //instance = NULL;
 instance = reinterpret_cast<instance_pointer>(unsigned_type(-1)); // bomb if used again
 delete inst;
}

template <typename INSTANCE, bool destroy_on_exit>
typename singleton<INSTANCE, destroy_on_exit>::volatile_instance_pointer
singleton<INSTANCE, destroy_on_exit>::instance = NULL;

STXXL_END_NAMESPACE

#endif // !STXXL_SINGLETON_HEADER