Question

我有一些c ++代码可以用clang 3.2-7和gcc 4.8.1编译，但不能用gcc 4.6.3编译。我正在用c ++ 0x编译。

我正在实施一个管理固定资源的'ResourcePool'。它通过提供带有自定义删除器类的unique_ptr来分配资源;当请求资源的对象超出范围时，删除器会将资源返回到池中。

删除类看起来像这样：

template <typename T>
class ResourcePoolManager {
public:
    ResourcePoolManager(ResourcePool<T> & pool)
    : pool(pool)
    {
    }

    ~ResourcePoolManager() {};

    void operator()(T* releasedResource) const {
        pool.releaseResource(releasedResource);
    }
private:
    ResourcePool<T> & pool;
};

池本身看起来像（编辑不相关的方法）：

template <typename T>
class ResourcePool {
public:
    ResourcePool()
    : manager(*this)
    {
    }

    std::unique_ptr<T, ResourcePoolManager<T>> requestResource() {
        if(availableResources.size() == 0) {
            return std::unique_ptr<T, ResourcePoolManager<T>>(NULL, manager);
        } else {
            T * resource = availableResources.front();
            availableResources.pop_front();
            return std::unique_ptr<T, ResourcePoolManager<T>>(resource, manager);
        }
    }
private:
    friend class ResourcePoolManager<T>;

    void releaseResource(T * releasedResource) {
        availableResources.push_back(releasedResource);
    }

    ResourcePoolManager<T> manager;
    std::deque<T *> availableResources;
    std::deque<T *> allResources;
};

当我尝试从池中提取资源并将其存储在std::vector;中时，会出现问题，其中OpenCLDevice是有问题的资源：

ResourcePool<OpenCLDevice> computeDevicePool;
std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice>> devicePtr = computeDevicePool.requestResource();
std::vector<std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice>>> gpus;
gpus.push_back(std::move(devicePtr));

正如前面提到的那样，clang和更新版本的gcc都可以。然而gcc 4.6.3正在推出：

/usr/include/c++/4.6/bits/unique_ptr.h: In member function 'std::unique_ptr<_Tp, _Dp>& std::unique_ptr<_Tp, _Dp>::operator=(std::unique_ptr<_Tp, _Dp>&&) [with _Tp = OpenCLDevice, _Dp = ResourcePoolManager<OpenCLDevice>, std::unique_ptr<_Tp, _Dp> = std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >]':
/usr/include/c++/4.6/bits/vector.tcc:319:4:   instantiated from 'void std::vector<_Tp, _Alloc>::_M_insert_aux(std::vector<_Tp, _Alloc>::iterator, _Args&& ...) [with _Args = {std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >}, _Tp = std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >, _Alloc = std::allocator<std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> > >, std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >*, std::vector<std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> > > >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer = std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >*]'
/usr/include/c++/4.6/bits/vector.tcc:102:4:   instantiated from 'void std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >}, _Tp = std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >, _Alloc = std::allocator<std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> > >]'
/usr/include/c++/4.6/bits/stl_vector.h:840:9:   instantiated from 'void std::vector<_Tp, _Alloc>::push_back(std::vector<_Tp, _Alloc>::value_type&&) [with _Tp = std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >, _Alloc = std::allocator<std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> > >, std::vector<_Tp, _Alloc>::value_type = std::unique_ptr<OpenCLDevice, ResourcePoolManager<OpenCLDevice> >]'
trunk/src/dpa/distinguishers/GenericOpenCLDPA.cpp:109:39:   instantiated from here
/usr/include/c++/4.6/bits/unique_ptr.h:176:2: error: use of deleted function 'ResourcePoolManager<OpenCLDevice>& ResourcePoolManager<OpenCLDevice>::operator=(const ResourcePoolManager<OpenCLDevice>&)'

ResourcePool.hpp:30:7 error: 'ResourcePoolManager<OpenCLDevice> & ResourcePoolManager<OpenCLDevice>::operator=(const ResourcePoolManager<OpenCLDevice>&)' 
is implicitly deleted because the default definition would be ill-formed:
ResourcePool.hpp:30:7: error: non-static reference member 'ResourcePool<OpenCLDevice>& ResourcePoolManager<OpenCLDevice>::pool', can't use default assignment operator

编译器在指针移动到gpus向量的最后一行停止，向我指示正在复制的东西不应该被复制。第30行是ResourcePoolManager类class ResourcePoolManager {的定义。

我是否对自定义删除器的管理做错了，新的编译器让我放弃了这些东西？

Answer 1

看起来像libstdc ++ 4.6 unique_ptr中的一个错误，它希望删除类型是可复制的。 Changing ResourcePoolManager::pool to a pointer instead of a reference is an effective workaround

更具体地说，该程序再现了错误：

#include <memory>
#include <vector>

struct deleter {
    deleter() : c(*"") {}
    void operator () (int *) const {}
    deleter(deleter&&) = default;
    deleter& operator = (deleter&&) = default;
    const char& c;
};

int main() {
    std::vector<std::unique_ptr<int, deleter>> vec;
    vec.push_back(std::unique_ptr<int, deleter>{});
}

简单地声明向量很好，push_back的实例化失败。

澄清：问题似乎是vector的4.6实现在调整大小时使用=移动赋值元素，而4.8实现仅使用移动构造。具有引用成员的类（例如您的删除者）可移动构造，但不能移动（或复制，可分配）可分配。 You can see the same error message in 4.8 if you assign to the vector：

int main() {
    std::vector<std::unique_ptr<int, deleter>> vec;
    vec.push_back(std::unique_ptr<int, deleter>{new int(42)});
    vec[0] = std::unique_ptr<int, deleter>{new int(42)};
}

指定

std::vector::push_back仅要求T为MoveInsertable，所以我相信这肯定是libstdc ++ 4.6中的一个错误。

具有自定义删除类的STL向量和unique_ptr

1 个答案: