c++ - 并发对象池提供 boost::shared_ptr

Question

我想实现一个并发对象池，其中返回一个 shared_ptr 并且不需要显式地将它返回到池中。我基本上在并发队列中为其分配了一个推送的 shared_ptr 数组，并实现了一个自定义删除器。似乎工作。我错过了什么吗？

#ifndef CONCURRENTOBJECTPOOL_H
#define CONCURRENTOBJECTPOOL_H

#include <boost/shared_ptr.hpp>
#include <boost/shared_array.hpp>
#include <tbb/concurrent_queue.h>

namespace COP
{

template<typename T>
class ConcurrentObjectPool;

namespace 
{
template<typename T>
class ConcurrentObjectPoolDeletor
{
public:
  ConcurrentObjectPoolDeletor(ConcurrentObjectPool<T>& aConcurrentObjectPool): 
  _concurrentObjectPool(aConcurrentObjectPool) {}

  void operator()(T *p) const;

private:
  ConcurrentObjectPool<T>& _concurrentObjectPool;  
};
} // Anonymous namespace for ConcurrentObjectPoolDeletor

template <typename T>
class ConcurrentObjectPool
{
 public:
 ConcurrentObjectPool(const unsigned int aPoolSize)
   : _goingDown(false),
     _poolSize(aPoolSize), 
     _pool(new T[_poolSize]),
     _ConcurrentObjectPoolDeletor(*this)
  {
    for(unsigned int i = 0; i < _poolSize; ++i)
      {
        boost::shared_ptr<T> curr(&_pool[i], _ConcurrentObjectPoolDeletor);
        _objectQueue.push(curr);
      }
  }

  boost::shared_ptr<T> loan()
  {
    boost::shared_ptr<T> curr;
    _objectQueue.pop(curr);
    return curr;
  }

  ~ConcurrentObjectPool()
  {
    _goingDown = true;
    _objectQueue.clear();
  }

 private:
  void payBack(T * p)
  {
    if (! _goingDown)
      {
        boost::shared_ptr<T> curr(p, _ConcurrentObjectPoolDeletor);
        _objectQueue.push(curr);
      }
  }

  bool _goingDown;
  const unsigned int _poolSize; 
  const boost::shared_array<T> _pool;
  const ConcurrentObjectPoolDeletor<T> _ConcurrentObjectPoolDeletor;
  tbb::concurrent_bounded_queue<boost::shared_ptr<T> > _objectQueue;
  friend class ConcurrentObjectPoolDeletor<T>;
};

namespace
{
template<typename T>
void ConcurrentObjectPoolDeletor<T>::operator()(T *p) const
{
  _concurrentObjectPool.payBack(p);
}
} // Anonymous namespace for ConcurrentObjectPoolDeletor

} // Namespace COP

#endif // CONCURRENTOBJECTPOOL_H

Answer 1

在 ConcurrentObjectPool 的析构函数中设置 _goingDown 标志和在 payBack() 中读取标志之间存在竞争。它可能导致内存泄漏。

实际上，如果您不尝试使析构函数安全地与 payBack() 同时运行，也许会更好。无论如何它都不安全，因为 _goingDown 标志是池对象的一部分，因此在池被销毁后访问它会导致未定义的行为 - 即所有对象都必须返回到池中在它被摧毁之前。