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// 2005 Olivier Galizzi, Janek Kozicki
// 2009 © Václav Šmilauer <eudoxos@arcig.cz>
#pragma once
#include <mutex>
#define FRIEND_SINGLETON(Class) friend class Singleton<Class>;
// use to instantiate the self static member.
#define SINGLETON_SELF(Class) template <> Class* Singleton<Class>::self = NULL;
// one singleton cannot access another in its constructor.
namespace {
std::mutex singleton_constructor_mutex;
}
template <class T> class Singleton {
protected:
static T* self; // must not be method-local static variable, since it gets created in different translation units multiple times.
public:
static T& instance()
{
if (!self) {
const std::lock_guard<std::mutex> lock(singleton_constructor_mutex);
if (!self) self = new T;
}
return *self;
}
};
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