Question

我在向此类添加复制构造函数时遇到问题： http://www.justsoftwaresolutions.co.uk/threading/implementing-a-thread-safe-queue-using-condition-variables.html

我需要添加它，以便我可以在stl向量容器中添加concurrent_queue。尝试下面，它几乎编译。实际上，如果我从复制构造函数中删除了_mutex和the_condition_variable，它就会编译。当我把它添加回来时它没有。关于编译，赋值运算符似乎没问题。

concurrent_queue(concurrent_queue<Data> const& rhs):
    the_queue(rhs.the_queue),
    the_mutex(rhs.the_mutex),
    the_condition_variable(rhs.the_condition_variable)
{
}

concurrent_queue<Data>& operator = (concurrent_queue<Data> const& rhs)
{
    if (this == &rhs) return *this; // check for self assignment

    the_queue = rhs.the_queue;
    the_mutex(rhs.the_mutex);
    the_condition_variable(rhs.the_condition_variable);
}

我得到的错误如下：

concurrentqueue.h: In copy constructor ‘concurrent_queue<Data>::concurrent_queue(const concurrent_queue<Data>&) [with Data = Packet*]’:
/usr/include/c++/4.4/bits/stl_construct.h:74:   instantiated from ‘void std::_Construct(_T1*, const _T2&) [with _T1 = concurrent_queue<Packet*>, _T2 = concurrent_queue<Packet*>]’
/usr/include/c++/4.4/bits/stl_uninitialized.h:187:   instantiated from ‘static void std::__uninitialized_fill_n<<anonymous> >::uninitialized_fill_n(_ForwardIterator, _Size, const _Tp&) [with _ForwardIterator = concurrent_queue<Packet*>*, _Size = long unsigned int, _Tp = concurrent_queue<Packet*>, bool <anonymous> = false]’
/usr/include/c++/4.4/bits/stl_uninitialized.h:223:   instantiated from ‘void std::uninitialized_fill_n(_ForwardIterator, _Size, const _Tp&) [with _ForwardIterator = concurrent_queue<Packet*>*, _Size = long unsigned int, _Tp = concurrent_queue<Packet*>]’
/usr/include/c++/4.4/bits/stl_uninitialized.h:318:   instantiated from ‘void std::__uninitialized_fill_n_a(_ForwardIterator, _Size, const _Tp&, std::allocator<_Tp2>&) [with _ForwardIterator = concurrent_queue<Packet*>*, _Size = long unsigned int, _Tp = concurrent_queue<Packet*>, _Tp2 = concurrent_queue<Packet*>]’
/usr/include/c++/4.4/bits/stl_vector.h:1035:   instantiated from ‘void std::vector<_Tp, _Alloc>::_M_fill_initialize(size_t, const _Tp&) [with _Tp = concurrent_queue<Packet*>, _Alloc = std::allocator<concurrent_queue<Packet*> >]’
/usr/include/c++/4.4/bits/stl_vector.h:230:   instantiated from ‘std::vector<_Tp, _Alloc>::vector(size_t, const _Tp&, const _Alloc&) [with _Tp = concurrent_queue<Packet*>, _Alloc = std::allocator<concurrent_queue<Packet*> >]’
test.cpp:18:   instantiated from here
concurrentqueue.h:24: error: no match for call to ‘(boost::mutex) (boost::mutex&)’

编辑：似乎boost mutex继承了non-copyable和condition变量，我认为是相同的。有趣的是，在作业中我能够复制它。为什么甚至会编译？我是否需要担心在我使用它的情况下它在实践中是不可复制的？

Answer 1

boost::mutex和boost::condition_variable都只有默认构造函数。除此之外，您不希望复制它们（可能被锁定）的状态 - 只需使用默认构造函数。

此外，您不应直接复制the_queue，因为这不是线程安全的。

Answer 2

AFAIK，boost::mutex和boost::condition不可复制（无论如何都没有复制互斥锁的意义）。使用复制构造函数中的默认构造函数构造它们，如下所示：

concurrent_queue(concurrent_queue<Data> const& rhs):
    the_queue(rhs.the_queue),
    the_mutex(),
    the_condition_variable()
{
}

请注意，problems可以使复制构造函数线程安全。如果你不是在线程之间复制对象，那应该不是问题。按照previous question中的想法，预先分配了所有concurrent_queue个对象，这应该不是问题。

如何向此类添加复制构造函数和赋值运算符？

2 个答案: