How to join a std::thread from itself (in C++11)

Question

I have a std::thread waiting and reading from a socket. And there is a pointer to this thread stored somewhere. But when something bad happens and the thread ends, I want it to call something that results in a function that will join this thread and then delete the pointer referring to it. (I have access to that pointer from within the thread)

I could do that in another thread but then that new thread becomes the problem.

Answer 1

Change your design so that you don't have this bizarre requirement. One simple solution is to use shared_ptr s to a control structure that owns the thread and has other status information as well. The thread can hold a shared_ptr to this control structure and use it to report its status to any other interested code. When nobody cares about this thread anymore, the last shared_ptr to this control structure will go away and it will be destroyed.

Answer 2

You could create your thread in a detached state, and make your thread lifetime dependent a condition variable and switch a boolean state on finish.

#include <thread>
#include <iostream>
#include <unistd.h>
#include <condition_variable>
#include <mutex>

class A {
    private:
        void Threadfunction();
        volatile bool class_running;
        volatile bool thread_running;
        std::condition_variable cv;
        std::mutex mu;
    public:
        A();
        ~A();
        void Stop();
};
A::A(){
    class_running = true;
    thread_running = false;
    std::thread t(&A::Threadfunction,this);
    t.detach();
}
A::~A(){
    if(class_running) {this->Stop();}
}
void A::Stop() {
    std::unique_lock<std::mutex> lk(mu);
    class_running = false;
    while(thread_running) {
        cv.wait(lk);
    }
    std::cout << "Stop ended " << std::endl;
}
void A::Threadfunction(){
    thread_running = true;
    std::cout << "thread started " << std::endl;
    while(class_running){
        // Do something
    }
    thread_running = false;
    cv.notify_one();
    std::cout << "thread stopped " << std::endl;
}
int main(){
    A a1;
    A a2;
    sleep(1);
    std::cout << "a1.Stop() called " << std::endl;
    a1.Stop();
    sleep(1);
    std::cout << "a2.Stop() not called but a2 goes out of scope and destructor is called " << std::endl;
}