id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
12293,boost::future::then lambda called before future is ready.,Jeffrey.Gramowski@…,viboes,"When chaining .then together with anther one and the previous .then returns a boost::future.  The lambda will get called before the future is ready.  I think what is happening is that the lambda is being called when the outer hidden future is ready.  I think that the callback shouldn't be called until the returned future is ready.

Here is the sample code which demonstrates the problem.

{{{
#!C++
// BoostFutureTest.cpp : Defines the entry point for the console application.
//

#include ""stdafx.h""

#include <future>
// boost version 1.60.0
// has the following set.
// #define BOOST_THREAD_VERSION 4
// #define BOOST_THREAD_PROVIDES_EXECUTORS

#include <boost\thread\future.hpp>


int _tmain(int argc, _TCHAR* argv[])
{
    int value = 0;
    int tmpValue = 0;
    boost::promise<void> promise1;
    boost::promise<void> promise2;

    auto future1 = promise1.get_future();

    auto waitFuture = future1.then([&tmpValue, &promise2](boost::future<void> future){
        assert(future.is_ready());  // this works correctly and is ready.

        std::async(std::launch::async, [&promise2, &tmpValue](){
            std::this_thread::sleep_for(std::chrono::seconds(1));
            tmpValue = 1;
            promise2.set_value();
        });

        return promise2.get_future();
    }).then([&value, &tmpValue](boost::future<void> future){
        // this lambda is being called before the future is ready.
        assert(future.is_ready());  // this doesn't work correctly and is not ready.

        // if we call future.get() this will block until the promise2 has been set be I don't want
        // the then lambda to block. I want the lambda called when the future is ready.

        value = tmpValue;
    });


    promise1.set_value();
    waitFuture.wait();

    std::cout << ""value = "" << value << std::endl; // should print 1 but prints 0
    return 0;
}
}}}",Bugs,closed,Boost 1.62.0,thread,Boost 1.60.0,Problem,fixed,future then,