C++单例模式Singleton内存回收

// Singleton.h
#ifndef _CSINGLETON_H_
#define _CSINGLETON_H_
 
class CSingleton
{
private:
	CSingleton() {};
	static CSingleton* _instance;
 
public:
	static CSingleton* GetInstance();
 
// ... other members or functions
public:
	void DoSomething();
};
 
#endif // _CSINGLETON_H_
 
// Singleton.cpp
#include "Singleton.h"
#include <windows.h>
#include <stdio.h>
 
CSingleton* CSingleton::_instance = NULL;
 
CSingleton* CSingleton::GetInstance()
{
	if (_instance == NULL)
	{
		_instance = new CSingleton();
	}
 
	return _instance;
}
 
void CSingleton::DoSomething()
{
	printf("void CSingleton::DoSomething() called.\n");
}
 
// 调用单例模式Singleton类
CSingleton::GetInstance()->DoSomething();

class CSingleton
{
private:
	CSingleton() {};
	static CSingleton* _instance;
 
public:
	static CSingleton* GetInstance();
 
// ... other members or functions
public:
	void DoSomething();
 
private:
	class Deleter
	{
	public:
		~Deleter()
		{
			if (CSingleton::_instance != NULL)
			{
				delete CSingleton::_instance;
			}
		}
	};
	// 定义一个静态的Deleter实例
	static Deleter deleter;
};

#define DISALLOW_COPY(TypeName) \
	TypeName(const TypeName&)
 
#define DISALLOW_ASSIGN(TypeName) \
	void operator=(const TypeName&)
 
#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
	TypeName(const TypeName&);               \
	void operator=(const TypeName&)
 
class CSingleton
{
public:
	static CSingleton &GetInstance()
	{
		static CSingleton instance;
		return instance;
	}
	void DoSomething()
	{
		printf("void CSingleton::DoSomething() called.\n");
	}
 
private:
	CSingleton() {};
	DISALLOW_COPY_AND_ASSIGN(CSingleton);
};
 
// 单例模式类使用
CSingleton::GetInstance().DoSomething();	// OK
CSingleton singleton = CSingleton::GetInstance(); // ERROR 不能通过编译

// at_exit.h
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef BASE_AT_EXIT_H_
#define BASE_AT_EXIT_H_
 
#include <stack>
 
#include "base/base_export.h"
#include "base/basictypes.h"
#include "base/callback.h"
#include "base/synchronization/lock.h"
 
namespace base {
 
// This class provides a facility similar to the CRT atexit(), except that
// we control when the callbacks are executed. Under Windows for a DLL they
// happen at a really bad time and under the loader lock. This facility is
// mostly used by base::Singleton.
//
// The usage is simple. Early in the main() or WinMain() scope create an
// AtExitManager object on the stack:
// int main(...) {
//    base::AtExitManager exit_manager;
//
// }
// When the exit_manager object goes out of scope, all the registered
// callbacks and singleton destructors will be called.
 
class BASE_EXPORT AtExitManager {
 public:
  typedef void (*AtExitCallbackType)(void*);
 
  AtExitManager();
 
  // The dtor calls all the registered callbacks. Do not try to register more
  // callbacks after this point.
  ~AtExitManager();
 
  // Registers the specified function to be called at exit. The prototype of
  // the callback function is void func(void*).
  static void RegisterCallback(AtExitCallbackType func, void* param);
 
  // Registers the specified task to be called at exit.
  static void RegisterTask(base::Closure task);
 
  // Calls the functions registered with RegisterCallback in LIFO order. It
  // is possible to register new callbacks after calling this function.
  static void ProcessCallbacksNow();
 
 protected:
  // This constructor will allow this instance of AtExitManager to be created
  // even if one already exists.  This should only be used for testing!
  // AtExitManagers are kept on a global stack, and it will be removed during
  // destruction.  This allows you to shadow another AtExitManager.
  explicit AtExitManager(bool shadow);
 
 private:
  base::Lock lock_;
  std::stack<base::Closure> stack_;
  AtExitManager* next_manager_;  // Stack of managers to allow shadowing.
 
  DISALLOW_COPY_AND_ASSIGN(AtExitManager);
};
 
#if defined(UNIT_TEST)
class ShadowingAtExitManager : public AtExitManager {
 public:
  ShadowingAtExitManager() : AtExitManager(true) {}
};
#endif  // defined(UNIT_TEST)
 
}  // namespace base
 
#endif  // BASE_AT_EXIT_H_

// at_exit.cc
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#include "base/at_exit.h"
 
#include <stddef.h>
#include <ostream>
 
#include "base/bind.h"
#include "base/callback.h"
#include "base/logging.h"
 
namespace base {
 
// Keep a stack of registered AtExitManagers.  We always operate on the most
// recent, and we should never have more than one outside of testing (for a
// statically linked version of this library).  Testing may use the shadow
// version of the constructor, and if we are building a dynamic library we may
// end up with multiple AtExitManagers on the same process.  We don't protect
// this for thread-safe access, since it will only be modified in testing.
static AtExitManager* g_top_manager = NULL;
 
AtExitManager::AtExitManager() : next_manager_(g_top_manager) {
// If multiple modules instantiate AtExitManagers they'll end up living in this
// module... they have to coexist.
#if !defined(COMPONENT_BUILD)
  DCHECK(!g_top_manager);
#endif
  g_top_manager = this;
}
 
AtExitManager::~AtExitManager() {
  if (!g_top_manager) {
    NOTREACHED() << "Tried to ~AtExitManager without an AtExitManager";
    return;
  }
  DCHECK_EQ(this, g_top_manager);
 
  ProcessCallbacksNow();
  g_top_manager = next_manager_;
}
 
// static
void AtExitManager::RegisterCallback(AtExitCallbackType func, void* param) {
  DCHECK(func);
  RegisterTask(base::Bind(func, param));
}
 
// static
void AtExitManager::RegisterTask(base::Closure task) {
  if (!g_top_manager) {
    NOTREACHED() << "Tried to RegisterCallback without an AtExitManager";
    return;
  }
 
  AutoLock lock(g_top_manager->lock_);
  g_top_manager->stack_.push(task);
}
 
// static
void AtExitManager::ProcessCallbacksNow() {
  if (!g_top_manager) {
    NOTREACHED() << "Tried to ProcessCallbacksNow without an AtExitManager";
    return;
  }
 
  AutoLock lock(g_top_manager->lock_);
 
  while (!g_top_manager->stack_.empty()) {
    base::Closure task = g_top_manager->stack_.top();
    task.Run();
    g_top_manager->stack_.pop();
  }
}
 
AtExitManager::AtExitManager(bool shadow) : next_manager_(g_top_manager) {
  DCHECK(shadow || !g_top_manager);
  g_top_manager = this;
}
 
}  // namespace base

base::AtExitManager exit_manager;