Starting a thread from a member function while inside another class's member function

问题

I need to start a thread that calls a public member function of the class Foo while inside of a public function that belongs to the class Bar. How do I achieve this?

I have tried the following (made trivial):

void Bar::BarFunc()
{ 
    // Do some BarFunc stuff 

    // Start a thread that needs to do stuff independently of BarFunc
    std::thread t(&Foo::FooFunc, FooFunc params,..,.., ???);
    t.detach();

    return;
}

This is my first time dealing with threading and the actual problem is a little more complex - BarFunc is a virtual function of a State class, with n-concrete classes implementing the different states my application can exist in, hence the question. I am not sure what to put as the last parameter, if anything. I have looked at this answer but cannot discern which syntax to use, if any of them even apply.

Finally, if this is bad practice all together, I would be grateful for any design advice.

回答1:

You likely have to manage two instances:

An instance of Foo
A thread executing a member function of Foo

That leads to the following sketch of a class Bar:

#include <iostream>
#include <thread>

struct Foo{
    void print(std::string s) { // by value!
        std::cout << s;
    }
};

class Bar{
    public:
    void hello() {
        // Ensure the thread is not running 
        // (Only one thread is supported in this example)
        if( ! foo_thread.joinable()) {
            // Move a newly constructed thread to the class member.
            foo_thread = std::thread(
                &Foo::print,        // pointer to member function of Foo
                &foo,               // pointer to the instance of Foo
                "hello\n"           // arguments by value
            );
        }
    }

    ~Bar() {
        // Ensure the thread has been started.
        if(foo_thread.joinable()) {
            // This will block until the thread has finished.
            foo_thread.join();
        }
    }

    private:
    Foo foo;
    std::thread foo_thread;
};

int main()
{
    Bar bar;
    bar.hello();
}

Note: The thread is not detached. A detached (not maintained properly) running thread, will get killed at end of the program and resources used by that thread (e.g.: file handles) might not be returned to the system.

来源：https://stackoverflow.com/questions/38110434/starting-a-thread-from-a-member-function-while-inside-another-classs-member-fun

标签

c++

multithreading

design-patterns

state