C++ 将引用变量传递给 g++-4.7.4 中的线程

Question

我需要启动一个线程，在线程启动时将复杂参数 (std::thread<>) 作为参数传递。我正在使用 `std::ref。此代码适用于更新的环境（g++-4.8.2 运行 on Ubuntu）。

现在我必须在旧编译器 (g++4.7.4) 中编译相同的代码，但出现错误。

代码如下所示，以及报错：

ReaderThread.hpp

class ReaderThread {
    void start(Reader reader, SyncController &syncController);
}

ReaderThread.cpp

void ReaderThread::start(Reader reader, SyncController &syncController)
{

        Do something...
}

main.cpp

int main()
{

    ...do stuff...

    /* 
     * Create and start the reader thread. The created object must live
     * during the whole thread life.
     * std::ref is used to pass as reference
     */
    myReader = ReaderFactory(params);

    std::shared_ptr<ReaderThread> ptr(new ReaderThread); 
    std::thread th(&ReaderThread::start, ptr, myReader, std::ref(syncController));


    ...do other stuff...
}

错误：

In file included from /usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/bits/move.h:57:0,
                 from /usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/bits/stl_pair.h:61,
                 from /usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/bits/stl_algobase.h:65,
                 from /usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/bits/char_traits.h:41,
                 from /usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/ios:41,
                 from /usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/ostream:40,
                 from /usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/iostream:40,
                 from ./main.cpp:11:
/usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/type_traits: In instantiation of 'struct std::_Result_of_impl<false, false, std::_Mem_fn<void (ReaderThread::*)(Reader, SyncController&)>, std::shared_ptr<ReaderThread>, Reader, std::reference_wrapper<SyncController> >':
/usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/type_traits:1857:12:   required from 'class std::result_of<std::_Mem_fn<void (ReaderThread::*)(Reader, SyncController&)>(std::shared_ptr<ReaderThread>, Reader, std::reference_wrapper<SyncController>)>'
/usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/functional:1563:61:   required from 'struct std::_Bind_simple<std::_Mem_fn<void (ReaderThread::*)(Reader, SyncController&)>(std::shared_ptr<aeirtuthread::ReaderThread>, Reader, std::reference_wrapper<SyncController>)>'
/usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/thread:133:9:   required from 'std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (ReaderThread::*)(Reader, SyncController&); _Args = {std::shared_ptr<ReaderThread>&, Reader&, std::reference_wrapper<SyncController>}]'
./aeirtu/aeirtu/main.cpp:155:96:   required from here
/usr/gcc-4.7.4/lib/gcc/i586-pc-linux-gnu/4.7.4/../../../../include/c++/4.7.4/type_traits:1834:9: error: no match for call to '(std::_Mem_fn<void (ReaderThread::*)(Reader, SyncController&)>) (std::shared_ptr<ReaderThread>, Reader, std::reference_wrapper<SyncController>)'

我无法确定此错误是由于在较旧的编译器上使用 std::ref 还是其他原因引起的。

感谢帮助找到 4.7.4 支持的修复程序并编译我的代码。

Answer 1

gcc 4.7 似乎无法处理作为对象提供的 shared_ptr（或 unique_ptr）。不过，它与自然指针一起工作得很好——所以一种可能的解决方案是用以下内容替换线程创建（当然，如果合适的话）：

std::thread th(&ReaderThread::start, &myThread, myReader, std::ref(syncController));

现在，如果这不可行并且需要真正分配的指针，以下是您的想法的替代品：

  std::thread th(
                 [ptr, &syncController, myReader] () {
                      ptr->start(myReader, syncController);
                 }
                );

}

在此示例中，synController 通过引用传递，其他所有内容均通过值传递，与 post.

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