firebird-mirror/src/common/classes/init.h

/*
 *	PROGRAM:	Common Access Method
 *	MODULE:		init.h
 *	DESCRIPTION:	InitMutex, InitInstance - templates to help with initialization
 *
 *  The contents of this file are subject to the Initial
 *  Developer's Public License Version 1.0 (the "License");
 *  you may not use this file except in compliance with the
 *  License. You may obtain a copy of the License at
 *  http://www.ibphoenix.com/main.nfs?a=ibphoenix&page=ibp_idpl.
 *
 *  Software distributed under the License is distributed AS IS,
 *  WITHOUT WARRANTY OF ANY KIND, either express or implied.
 *  See the License for the specific language governing rights
 *  and limitations under the License.
 *
 *  The Original Code was created by Alexander Peshkoff
 *  for the Firebird Open Source RDBMS project.
 *
 *  Copyright (c) 2004 Alexander Peshkoff <peshkoff@mail.ru>
 *  and all contributors signed below.
 *
 *  All Rights Reserved.
 *  Contributor(s): ______________________________________.
 */

#ifndef CLASSES_INIT_INSTANCE_H
#define CLASSES_INIT_INSTANCE_H

#include "fb_types.h"
#include "../common/classes/alloc.h"

namespace Firebird {

// InstanceControl - interface for almost all global variables

class InstanceControl
{
public:
	InstanceControl();
	static void destructors();
	static void registerGdsCleanup(FPTR_VOID cleanup);
protected:
	virtual void dtor() = 0;
private:
	static InstanceControl* instanceList;
	static FPTR_VOID gdsCleanup;
	InstanceControl* next;
};

// GlobalPtr - template to help declaring global varables

template <typename T>
class GlobalPtr : private InstanceControl
{
private:
	T* instance;
	void dtor()
	{
		delete instance;
		instance = 0;
	}
public:
	GlobalPtr() 
		: InstanceControl()
	{
		instance = FB_NEW(*getDefaultMemoryPool()) T(*getDefaultMemoryPool());
		// This means - for objects with ctors/dtors that want to be global,
		// provide ctor with MemoryPool& parameter. Even if it is ignored!
	}
	T* operator->() throw()
	{
		return instance;
	}
	operator T&() throw()
	{
		return *instance;
	}
	T* operator&() throw()
	{
		return instance;
	}
	bool operator!() const throw()
	{
		return instance ? false : true;
	}
};

// Support for common mutex for various inits

class StaticMutex
{
protected:
	static Mutex* mutex;
public:
	static void create();
	static void release();
};

// InitMutex - executes static void C::init() once and only once

template <typename C>
class InitMutex : private StaticMutex
{
private:
	volatile bool flag;
public:
	InitMutex() 
		: flag(false) { }
	void init() 
	{
		if (!flag) {
			MutexLockGuard guard(*mutex);
			if (!flag) {
				C::init();
				flag = true;
			}
		}
	} 
	void cleanup() 
	{
		if (flag) {
			MutexLockGuard guard(*mutex);
			if (flag) {
				C::cleanup();
				flag = false;
			}
		}
	} 
};

// InitInstance - initialize pointer to class once and only once,
// DefaultInit uses default memory pool for it.

template <typename T>
class DefaultInit 
{
public:
	static T* init() 
	{
		return FB_NEW(*getDefaultMemoryPool()) T(*getDefaultMemoryPool());
	}
};

template <typename T, 
	typename I = DefaultInit<T> >
class InitInstance : private StaticMutex
{
private:
	T* instance;
	volatile bool flag;
public:
	InitInstance() 
		: flag(false) { }
	T& operator()() 
	{
		if (!flag) {
			MutexLockGuard guard(*mutex);
			if (!flag) {
				instance = I::init();
				flag = true;
			}
		}
		return *instance;
	}
};

} //namespace Firebird

#endif // CLASSES_INIT_INSTANCE_H