2

一般来说，我是std::threadC++11 的新手。尝试使用https://en.cppreference.com/w/cpp/thread/thread/thread中的示例，我试图查看是否可以std::thread使用具有非空参数列表的类成员函数调用运算符生成一个如下面的代码所示：

// main.cpp

#include <iostream>
#include <iostream>
#include <thread>

class Foo {
public:

  void operator()( int& i ) {
    std::cout << i << std::endl;
  }
};

int main( int argc, char* argv[] ) {
  Foo f;
  int i = 42;

  std::thread t1( f, i );
  t1.join();

  return 0;
}

错误消息很神秘：

$ g++ --version && g++ ./main.cpp -lpthread && ./a.out
g++ (Debian 6.3.0-18+deb9u1) 6.3.0 20170516
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

In file included from /usr/include/c++/6/thread:39:0,
                 from ./main.cpp:5:
/usr/include/c++/6/functional: In instantiation of ‘struct std::_Bind_simple<Foo(int)>’:
/usr/include/c++/6/thread:138:26:   required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = Foo&; _Args = {int&}]’
./main.cpp:19:24:   required from here
/usr/include/c++/6/functional:1365:61: error: no type named ‘type’ in ‘class std::result_of<Foo(int)>’
       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<Foo(int)>’
         _M_invoke(_Index_tuple<_Indices...>)

相反，空参数列表调用运算符工作正常：

// main.cpp

#include <iostream>
#include <iostream>
#include <thread>

class Foo {
public:

  void operator()() {
    std::cout << 42 << std::endl;
  }
};

int main( int argc, char* argv[] ) {
  Foo f;
  int i = 42;

  std::thread t1( f );
  t1.join();

  return 0;
}

$ g++ --version && g++ ./main.cpp -lpthread && ./a.out
g++ (Debian 6.3.0-18+deb9u1) 6.3.0 20170516
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

42

我的第一次尝试是否可行 - 我只是有语法错误吗？有没有办法使用对象及其非空参数列表调用运算符生成 std​​::thread ？

我相信这个问题与Start thread with member function不同，因为这个问题专门关于使用成员对象调用运算符生成线程我知道这可以用 lambdas 完成。

4

1 回答 1

3

std::thread除非你是明确的，否则不会让你通过引用传递，因为它是生命周期问题的一个简单来源。使用std::ref明确表示您i通过引用传递：

std::thread t1( f, std::ref(i) );

或者，按值传递。在通过引用将某些内容传递给线程之前请仔细考虑，并确保它是必要的。您传递的变量必须比它在线程内的使用时间长。

于 2020-09-22T04:08:21.723 回答