Unexpected output with boost coroutine2

Question

This is the test case

#include <boost/coroutine2/all.hpp>

#include <iostream>
#include <cassert>

int main() {
    auto sum = 0;
    using Coroutine_t = boost::coroutines2::coroutine<int>::push_type;
    auto coro = Coroutine_t{[&](auto& yield) {
        for (;;) {
            auto val = yield.get();
            std::cout << "Currently " << val << std::endl;
            sum += val;
            yield(); // jump back to starting context
         }
    }};

    std::cout << "Transferring 1" << std::endl;
    coro(1); // transfer {1} to coroutine-function
    std::cout << "Transferring 2" << std::endl;
    coro(2); // transfer {1} to coroutine-function

    // assert(sum == 3);
}

For some reason the assert at the end fails with the value of sum being 14 I installed boost (version 1.63) context with the command

./bootstrap.sh --prefix=build --with-libraries=context
./b2 --prefix=build --with-context

I am running this on a MacOS 10.12.6. The compile command was

g++ -std=c++14 -O3 -I boost co.cpp boost/stage/lib/libboost_*.a

Where boost is the boost folder downloaded from sourceforge.

The output of the above test case strangely without the assert is this

Transferring 1
Currently 0
Transferring 2
Currently 2
Currently 2

Why is the first line printed in the coroutine Currently 0? Also why is Currently 2 is printed twice here?? The latter can be seen here as well https://wandbox.org/permlink/zEL9fGT5MrzWGgQB

---

For the second question it seems like after the main thread has finished, control is transferred back to the coroutine one last time. Why is that? That seems strange..

UPDATE : For the second question, it seems to be different in boost 1.65??!? https://wandbox.org/permlink/JQa9Wq1jp8kB49Up

Answer 1

output of your app with boost-1.65.1 is:

Transferring 1
Currently 1
Transferring 2
Currently 2

probably your problem was caused by bug that has been fixed in boost-1.63