/usr/include/mapnik/util/singleton.hpp is in libmapnik-dev 3.0.12+ds-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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*
* This file is part of Mapnik (c++ mapping toolkit)
*
* Copyright (C) 2015 Artem Pavlenko
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
*****************************************************************************/
#ifndef MAPNIK_UTIL_SINGLETON_HPP
#define MAPNIK_UTIL_SINGLETON_HPP
#include <mapnik/config.hpp>
// stl
#include <stdexcept> // std::runtime_error
#include <cstdlib> // std::atexit
#include <new> // operator new
#include <type_traits>
#include <atomic>
#ifdef MAPNIK_THREADSAFE
#include <mutex>
#endif
namespace mapnik
{
template <typename T>
class CreateUsingNew
{
public:
static T* create()
{
return new T;
}
static void destroy(T* obj)
{
delete obj;
}
};
template <typename T>
class CreateStatic
{
private:
using storage_type = typename std::aligned_storage<sizeof(T), alignof(T)>::type;
public:
static T* create()
{
static storage_type static_memory;
return new(&static_memory) T;
}
static void destroy(volatile T* obj)
{
obj->~T();
}
};
#ifdef __GNUC__
template <typename T,
template <typename U> class CreatePolicy=CreateStatic> class MAPNIK_DECL singleton
{
#else
template <typename T,
template <typename U> class CreatePolicy=CreateStatic> class singleton
{
#endif
friend class CreatePolicy<T>;
static std::atomic<T*> pInstance_;
static std::atomic<bool> destroyed_;
singleton(const singleton &rhs);
singleton& operator=(const singleton&);
static void onDeadReference()
{
throw std::runtime_error("dead reference!");
}
static void DestroySingleton()
{
CreatePolicy<T>::destroy(pInstance_);
pInstance_ = 0;
destroyed_ = true;
}
protected:
#ifdef MAPNIK_THREADSAFE
static std::mutex mutex_;
#endif
singleton() {}
public:
static T& instance()
{
T * tmp = pInstance_.load(std::memory_order_acquire);
if (tmp == nullptr)
{
#ifdef MAPNIK_THREADSAFE
std::lock_guard<std::mutex> lock(mutex_);
#endif
tmp = pInstance_.load(std::memory_order_relaxed);
if (tmp == nullptr)
{
if (destroyed_)
{
destroyed_ = false;
onDeadReference();
}
else
{
tmp = CreatePolicy<T>::create();
pInstance_.store(tmp, std::memory_order_release);
#ifndef MAPNIK_NO_ATEXIT
// register destruction
std::atexit(&DestroySingleton);
#endif
}
}
}
return *tmp;
}
};
#ifdef MAPNIK_THREADSAFE
template <typename T,
template <typename U> class CreatePolicy> std::mutex singleton<T,CreatePolicy>::mutex_;
#endif
template <typename T,
template <typename U> class CreatePolicy> std::atomic<T*> singleton<T,CreatePolicy>::pInstance_;
template <typename T,
template <typename U> class CreatePolicy> std::atomic<bool> singleton<T,CreatePolicy>::destroyed_(false);
}
#endif // MAPNIK_UTIL_SINGLETON_HPP
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