SingletonMacros.h

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/*
 * This file is a part of the Biology project by eons LLC.
 * Biology (aka Develop Biology) is a framework for approaching software
 * development from a natural sciences perspective.
 *
 * Copyright (C) 2022 Séon O'Shannon & eons LLC
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include <cstddef>
#include <new>
 
// BIO_SINGLETON emits a class deriving `virtual public ::bio::ThreadSafe`, so
// the singleton retains its own lock regardless of its base. That type must be
// visible wherever the macro is expanded. Historically this was satisfied only
// transitively (e.g. via Container -> ThreadSafe); now that Container no longer
// carries a ThreadSafe base (v8 layout), include it here so the macro is
// self-sufficient. ThreadSafe.h's only include is Macros.h (pragma-once), and
// the macros ThreadSafe.h consumes (BIO_THREAD_ENFORCEMENT_LEVEL,
// BIO_CPP_VERSION, BIO_OS_IS_LINUX) are defined by Optimize/Language/OS macros
// that Macros.h includes before this header, so there is no ordering hazard.
#include "bio/common/thread/ThreadSafe.h"
 
namespace bio {
 
namespace pointer_arena {
void* Allocate(
    ::std::size_t bytes,
    ::std::size_t align);
}
 
typedef void* (*SingletonCreator)();
 
void* GetOrCreateSingleton(
    const char* key,
    SingletonCreator creator
);
 
} //bio namespace
 
//@formatter:off
#if BIO_COMPACT_POINTER_STORAGE
    #define BIO_SINGLETON_CREATE_INSTANCE(className)                           \
        void* storage = ::bio::pointer_arena::Allocate(                        \
            sizeof(className),                                                 \
            __alignof__(className));                                           \
        if (!storage)                                                          \
        {                                                                      \
            throw ::std::bad_alloc();                                          \
        }                                                                      \
        return new (storage) className();
#else
    #define BIO_SINGLETON_CREATE_INSTANCE(className)                           \
        return new className();
#endif
//@formatter:on
 
#define BIO_SINGLETON(className, baseClass)                                    \
class className :                                                              \
    public baseClass,                                                          \
    virtual public ::bio::ThreadSafe                                           \
{                                                                              \
public:                                                                        \
    static className& Instance()                                               \
    {                                                                          \
        return *static_cast<className*>(                                       \
            ::bio::GetOrCreateSingleton(                                       \
                #className,                                                    \
                &className::CreateInstance));                                  \
    }                                                                          \
private:                                                                       \
    static void* CreateInstance()                                              \
    {                                                                          \
        BIO_SINGLETON_CREATE_INSTANCE(className)                               \
    }                                                                          \
    className()                                                                \
    {                                                                          \
    }                                                                          \
    className(className const &);                                              \
    void operator=(className const &);                                         \
};