Is there a way to cancel/detach a future in C++11?

Question

I have the following code:

#include 
#include 
#include 
#include 

using namespace std;

int sleep         


        

Answer 1

I know this is an old question, but it still comes up as the top result for "detach std::future" when searching. I came up with a simple template based approach to handle this:

template 
std::future startDetachedFuture(FUNCTION_TYPE func) {
    std::promise pro;
    std::future fut = pro.get_future();

    std::thread([&func](std::promise p){p.set_value(func());},
                std::move(pro)).detach();

    return fut;
}

and you use it like so:

int main(int argc, char ** argv) {
    auto returner = []{fprintf(stderr, "I LIVE!\n"); sleep(10); return 123;};

    std::future myFuture = startDetachedFuture(returner);
    sleep(1);
}

output:

$ ./a.out 
I LIVE!
$

If myFuture goes out of scope and is destructed, the thread will carry on doing whatever it was doing without causing problems because it owns the std::promise and its shared state. Good for occasions where you only sometimes would prefer to ignore the result of a computation and move on (my use case).

To the OP's question: if you get to the end of main it will exit without waiting for the future to finish.