Bad Memory Access in boost::future<>.then() after accessing given future

[Stephan Mehlhase <s.mehlhase@…>]

When using "then" on a future and accessing the value of the future in the continuation, the memory of the future is freed/released and the further execution of the continuation happens in an undefined limbo state (leading to a crash with EXC_BAC_ACCESS at least on iOS.

Here is a minimal example:

#define BOOST_THREAD_VERSION 4
#include <boost/thread.hpp>

class Test {

public:
    void test() {
        boost::shared_ptr<Test> listener(new Test());
        boost::future<bool> con = boost::make_future(true);
        listener->foo(); // Works
        boost::future<bool> initDone = con.then([listener](boost::future<bool>& connected) {
            listener->foo(); // Works
            if (!connected.get()) {
                listener->foo();
                return false;
            }
            listener->foo();  // EXC_BAD_ACCESS
            return true;
        });
    }

    void foo() {
        std::cout << "foo";
    }
};

[Stephan Mehlhase <s.mehlhase@…>]

Debugger View after get() has been called in continuation

[viboes]

I'm aware of the bug. future<>.then is not stable yet. this is why I have not delivered it yet, that is is not in the documentation. Sorry for this.

[viboes]

You could try with

#define BOOST_THREAD_DONT_PROVIDE_FUTURE_INVALID_AFTER_GET

but even with this future<>.then is not stable yet.

[Stephan Mehlhase <s.mehlhase@…>]

Thanks, with disabling the invalidation it seems to work. However, since it is not considered stable yet, I'll switch to using a separate thread in which I'll wait for the future and execute the needed actions afterwards.

[viboes]

I close the ticket as invalid as the feature is not delivered yet, but I have in mind that this doesn't works yet.