弱回调示例

#include <iostream>
#include <memory>
#include <string>
#include <map>
#include <functional>
#include <stdio.h>
#include <assert.h>
using namespace std::placeholders;
using namespace std;

class Stock
{
public:
    Stock(const string& name) :name_(name)
    { 
        printf("Stock[%p] %s\n", this, name_.c_str());
    }
    ~Stock()
    {
        printf("~Stock[%p] %s\n", this, name_.c_str());
    }
    const string& key() const { return name_; }
private:
    string name_;
};

class StockFactory :public enable_shared_from_this<StockFactory>
{
public:
    StockFactory()
    {
        printf("StockFactory[%p]\n", this);
    }

    ~StockFactory()
    {
        printf("~StockFactory[%p]\n", this);
    }

    shared_ptr<Stock> get(const string& key)
    {
        shared_ptr<Stock> pStock;
        weak_ptr<Stock>& pWeakStock = stocks_[key];
        pStock = pWeakStock.lock();
        if (!pStock)
        {
            pStock = shared_ptr<Stock>(new Stock(key), bind(&StockFactory::weakDelCb, weak_ptr<StockFactory>(shared_from_this()), _1));
            pWeakStock = pStock;
        }
        return pStock;
    }
private:
    static void weakDelCb(const weak_ptr<StockFactory>& factory, Stock* stock)
    {
        shared_ptr<StockFactory>  pFactory(factory.lock());
        if (pFactory)
        {
            pFactory->removeStock(stock);
        }
        else
        {
            printf("factory has died\n");
        }
        delete stock;
    }

    void removeStock(Stock* pStock)
    {
        printf("removeStock [%p]\n", pStock);
        if (pStock)
        {
            auto iter = stocks_.find(pStock->key());
            if (iter != stocks_.end() && iter->second.expired())
            {
                stocks_.erase(pStock->key());
            }
        }
    }
private:
    map<string, weak_ptr<Stock>> stocks_;
};

void testFactoryLongLife()
{
    shared_ptr<StockFactory> factory(new StockFactory);
    {
        shared_ptr<Stock>  stock1 = factory->get("daniel");
        shared_ptr<Stock>  stock2 = factory->get("daniel");
        assert(stock1 == stock2);
    }
}

void testFactoryShortLife()
{
    shared_ptr<Stock> stock1;
    {
        shared_ptr<StockFactory> factory(new StockFactory);
        stock1 = factory->get("daniel");
        shared_ptr<Stock>  stock2 = factory->get("daniel");
        assert(stock1 == stock2);
    }
}

int main(int argc, char **agrv)
{
    testFactoryLongLife();
    testFactoryShortLife();
    system("pause");
    return 0;
}