C++ Thread类

c++ thread类:

class myFunc{
public:
    void operator()(string s){
        print("functor", s, " ");
        s = "fgih";
    }
};

void test(){
    myFunc fun;

    string s("abcd");
    thread t4(fun, s);
    t4.join();
    print(s);
}

输出:

functor abcd
abcd

Clion编译出错：

CMakeFiles/15_IPC.dir/main.cpp.o：在函数‘shm_mutex_test()’中：
/home/enheng/CLionProjects/15_IPC/main.cpp:257：对‘pthread_mutexattr_init’未定义的引用
/home/enheng/CLionProjects/15_IPC/main.cpp:258：对‘pthread_mutexattr_setpshared’未定义的引用

解决办法：

在CMakeLists.txt添加：

find_package(Threads REQUIRED)
target_link_libraries(15_IPC Threads::Threads)

将程序修改为引用:

    void operator()(string &s){
        print("functor", s, " ");
        s = "fgih";
    }

程序报错:

/usr/include/c++/6/functional: In instantiation of ‘struct std::_Bind_simple<myFunc(std::__cxx11::basic_string<char>)>’:
/usr/include/c++/6/thread:138:26:   required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = myFunc&; _Args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&}]’
/home/enheng/CLionProjects/11_thread/main.cpp:353:21:   required from here
/usr/include/c++/6/functional:1365:61: error: no type named ‘type’ in ‘class std::result_of<myFunc(std::__cxx11::basic_string<char>)>’
       typedef typename result_of<_Callable(_Args...)>::type result_type;
                                                             ^~~~~~~~~~~
/usr/include/c++/6/functional:1386:9: error: no type named ‘type’ in ‘class std::result_of<myFunc(std::__cxx11::basic_string<char>)>’
         _M_invoke(_Index_tuple<_Indices...>)
         ^~~~~~~~~

再修改:

class myFunc{
public:
    void operator()(string &s){
        print("functor", s, " ");
        s = "fgih";
    }
};

void test(){
    myFunc fun;

    string s("abcd");
    thread t4(fun, ref(s));
    t4.join();
    print(s);
}

输出:

functor abcd
fgih

"Note that template type deduction is (correctly) deducing the type of value to be int, but this doesn’t match the type int&that it sees in start_thread. "

模板推导值的类型是int, 但是不匹配接收类型int &.

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所以要用std::ref来传递引用.

 
       reference_wrapper 
      

(C++11)

可复制构造 (CopyConstructible) 且可复制赋值 (CopyAssignable) 的引用包装器

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