C++ std::thread 线程的传参方式

C++ std::thread 线程的传参方式

flyfish

标准 C++11

传递一个函数的方式

#include <iostream>
#include <thread>

void thread_function()
{
  
    std::cout << "thread function\n";
}

int main()
{
  
    std::thread t(&thread_function);   // t starts running
    std::cout << "main thread\n";
    t.join();   // 主线程等待线程t完成
    std::cout << "end\n";
    return 0;
}

柏拉图理念世界的样子

柏拉图可感世界的样子

结果

main thread
thread function
end

传值的方式

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

void thread_function(std::string s)
{
  
    std::cout << "t thread is = " << s << std::endl;
}

int main()
{
  
    std::string s = "abc";
    std::thread t(&thread_function, s);
    std::cout << "main thread message = " << s << std::endl;
    t.join();
    return 0;
}

main thread message = abc
t thread is = abc

传址的方式

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


void thread_function(std::string &s)
{
  
    std::cout << "t thread is = " << s << std::endl;
    s = "cde";
}
int main()
{
  
    std::string s = "abc";
    std::thread t(&thread_function, std::ref(s));
    t.join();
    std::cout << "main thread message = " << s << std::endl;

    return 0;
}

结果

t thread is = abc
main thread message = cde

在线程之间不共享内存（不复制）的方式

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


void thread_function(std::string s)
{
    std::cout << "t thread is = " << s << std::endl;
    s = "cde";
}
int main()
{
    std::string s = "abc";
    std::thread t(&thread_function, std::move(s));
    t.join();
    std::cout << "main thread message = " << s << std::endl;

    return 0;
}

结果

t thread is = abc
main thread message = 

函数对象的方式

#include <iostream>
#include <thread>

class thread_obj {
  
public:
    void operator()(int x)
    {
  
        for (int i = 0; i < x; i++)
            std::cout << "Thread using function object as callable\n";
    }
};

int main()
{
  
    std::thread th(thread_obj(), 3);
    th.join();
    return 0;
}

Lambda 表达式的方式

#include <iostream>
#include <thread>

int main()
{
  

    // Define a Lambda Expression
    auto f = [](int x) {
  
        for (int i = 0; i < x; i++)
            std::cout << "Thread using lambda expression as callable\n";
    };

    std::thread th(f, 3);
    th.join();

    return 0;
}

传递类的成员函数的方式

#include <thread>
#include <iostream>

class SayHello
{
public:
    void greeting(std::string const& message) const
    {
        std::cout<<message<<std::endl;
    }
};

int main()
{
    SayHello x;
    std::thread t(&SayHello::greeting,&x,"hello");
    t.join();
}

堆分配对象的方式

#include <thread>
#include <iostream>
class SayHello
{
  
public:
    void greeting(std::string const& message) const
    {
  
        std::cout<<message<<std::endl;
    }
};

int main()
{
  
    std::shared_ptr<SayHello> p(new SayHello);
    std::thread t(&SayHello::greeting,p,"hello");
    t.join();
}

线程可移动构造 (MoveConstructible) 或移动赋值 (MoveAssignable) ；

不可复制构造 (CopyConstructible) 或复制赋值 (CopyAssignable)

#include <iostream>
#include <thread>

void thread_function()
{
  
    std::cout << "t thread function\n";
}

int main()
{
  
    std::thread t(&thread_function);
    std::cout << "main thread\n";
    std::thread t2 = std::move(t);

    t2.join();

    return 0;
}

结果

main thread
t thread function