StockFactory.cpp

#include <iostream>
#include <memory>
#include <mutex>
#include <unordered_map>

using namespace std;

class Stock
{
 public:
  Stock(const string& name)
    : name_(name)
  {
  }

  const string& key() const { return name_; }

 private:
  string name_;
};

// 对象池
class StockFactory
{
 public:

  std::shared_ptr<Stock> get(const string& key)
  {
    std::shared_ptr<Stock> pStock;
    std::lock_guard<std::mutex> lock(mutex_);
    std::weak_ptr<Stock>& wkStock = stocks_[key];
    pStock = wkStock.lock();
    if (!pStock)
    {
      pStock.reset(new Stock(key),
                   [this] (Stock* stock) { deleteStock(stock); });
      wkStock = pStock;
    }
    return pStock;
  }

 private:

void deleteStock(Stock* stock)
  {
    if (stock)
    {
      muduo::MutexLockGuard lock(mutex_);
      auto it = stocks_.find(stock->key());
      assert(it != stocks_.end());
      if (it->second.expired())
      {
        stocks_.erase(it);
      }
    }
    delete stock;
  }

  mutable std::mutex mutex_;
  std::unordered_map<string, std::weak_ptr<Stock> > stocks_;
};