/usr/include/stxxl/bits/singleton.h is in libstxxl-dev 1.4.1-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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* include/stxxl/bits/singleton.h
*
* Part of the STXXL. See http://stxxl.sourceforge.net
*
* Copyright (C) 2008, 2011 Andreas Beckmann <beckmann@cs.uni-frankfurt.de>
*
* 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
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