对象池StockFactory

原创已于 2023-04-21 14:26:56 修改 · 123 阅读

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#c++ #linux

于 2023-04-21 14:17:31 首次发布

该文章介绍了一个使用C++实现的StockFactory类，该类继承了boost库的enable_shared_from_this和noncopyable，用于管理Stock对象的生命周期。get方法利用mutex保证线程安全，并通过weak_ptr避免循环引用。在weakDeleteCallback回调中，安全删除Stock实例。测试案例展示了长期和短期工厂实例的不同行为。

class StockFactory:public boost::enable_shared_from_this<StockFactory>,
				   boost::noncopyable
{
public:
	shared_ptr<Stock> get(const string& key){
		shared_ptr<Stock> pStock;
		MutexLockGuard lock(mutex_);
		weak_ptr<Stock>& wkStock=stocks_[key]; //注意wkStock是引用
		if(!pStock){
			pStock.reset(new Stock(key),
						boost:bind(&StockFactory::weakDeleteCallback,
						boost::weak_ptr<StockFactory>(shared_from_this),
						_1));
			//上面必须强制把shared_from_this()转型为weak_ptr，才不会延长生命期，
			//因为boost:bind拷贝的是实参类型，不是形参类型
			wkStock=pStock;
		}
		return pStock;
	}
private:
	static void weakDeleteCallback(const boost:weak_ptr<StockFactory>& wkFactor,
									Stock* stock){
		shared_ptr<StockFactory>factory(wkFactory.lock());//尝试提升
		if(factory){
			factory->removeStock(stock);
		}
		delete stock;
	}

	void removeStock(Stock* stock){
		if(stock){
			MutexLockGuard lock(mutex_);
			stocks_erase(stock->key);
		}
	}

private:
	mutable MutexLock mutex_;
	std::map<string, weak_ptr<Stock>>stocks_;
}

两个简单的测试：

void testLongLifeFactory(){
	shared_ptr<Stock> stock=fatcory->get("NYSE:IBM");
	shared_ptr<Stock> stock2=fatcory->get("NYSE:IBM");
	assert(stock==stock2);
}

void testShortLifeFactory(){
	shared_ptr<Stock> stock;
	{
		shared_ptr<StockFatcory> fatcory(new StockFatcory);
		stock=fatcory->get("NYSE:IBM");
		shared_ptr<Stock> stock2=fatcory->get("NYSE:IBM");
		assert(stock==stock2);
	}
}