boost::future and continuations - value set, but future still blocks

Question

I am trying to make the following continuation work - but f.get() blocks. Whats wrong?

#include 

#define BOOST_THREAD_PROVIDES_FUTU         


        

Answer 1

The problem is, your composed future is not kept around. In fact, it is a temporary and it gets destructed as soon as the statement (with .then()) ends.

Fix it:

int main () {
    Foo foo;

    auto f1 = foo.start();
    auto f2 = f1.then([](boost::future<int> f) {
        std::cout << "done:" << std::endl;
        std::cout << f.get() << std::endl;
    });

    foo.finish();
    f2.get();
}

Now it prints

done:
23

See it Live On Coliru

If you move the f2.get() before the foo.finish() it will dead lock again.