September 2019 - Boost-users

[asio] using fork in coroutine composed operations
by Stephan Menzel 10 Sep '19

10 Sep '19

Hello all, my experiments with custom composed operations in asio have led me to another question regarding the use of such methods. What do I do in order to have multiple handlers in flight, e.g. for a timer? My example is here: https://github.com/MrMoose/moose_tools/blob/master/TimedConnect.hpp I'm trying to realize an old dream in asio. A function that will take a socket and asynchronously do a resolve and connect to the result while having a timeout around the operation. Here in the test cases (lower part) is how I imagine usage: https://github.com/MrMoose/moose_tools/blob/master/test/TestAsioHelpers.cpp… This works (the unit test does...) but I think it's no good and illustrate the problem. In the coroutine impl I can safely jump in and out and resume the code represented by the coroutine object as was explained to me yesterday. But what can I do with the timer? I cannot std::move(self) into it because it gets moved again moments later and I cannot yield on the timer wait operation. I want the timer handler and the async ops handlers both be in flight and have called whichever completes first. I tried coroutine fork thinking it might be the right tool but that seems to clash with the move-self-ahead pattern which is used here. If I don't yield and set the timer to a fixed lambda (as in the example above) it seems to work but I guess that's not how it's supposed to be, right? Any hints as to how I can make this better? Cheers, Stephan

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Program Options MacOS Error
by Michael Chiu 10 Sep '19

10 Sep '19

Hi All, I was trying to use boost program options to capture a std::string like the examples in the documentation. However I keep getting the error: libc++abi.dylib: terminating with uncaught exception of type boost::wrapexcept<boost::bad_any_cast> when i try to retrieve the value from the valuemap, i.e. vm["source"].as<std::string>(); The code that I have (which right now is essentially the tutorial example) runs fine on linux but has the above error on macos. Am i doing something wrong or is this a genuine platform specific bug? Sincerely, --Michael

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Re: [Boost-users] xlcpp: use of undeclared identifier 'decltype' used in boost/thread/lockable_traits.hpp
by Roy Musselman 10 Sep '19

10 Sep '19

Greetings, While attempting to build boost 1.70.0 for IBM Power9 using the IBM XL compilers using the SPACK tool, the following errors occur repeatedly for every header file that eventually includes boost/thread/lockable_traits.hpp In file included from ./boost/thread/lock_types.hpp:14: ./boost/thread/lockable_traits.hpp:157:11: error: use of undeclared identifier 'decltype' decltype(void(boost::declval<T&>().lock())) ^ ./boost/thread/lockable_traits.hpp:165:11: error: use of undeclared identifier 'decltype' decltype(void(boost::declval<T&>().unlock())) ^ ./boost/thread/lockable_traits.hpp:173:11: error: use of undeclared identifier 'decltype' decltype(bool(boost::declval<T&>().try_lock())) ^ These errors could be resolved if the -std=c++11 compiler option is used. Attempting to use SPACK options cxxflags=-std=c++11 or cxxstd=11 failed as if they were ignored. I was able to work-around this pervasive error by adding the following line to the file tools/build/src/tools/xlcpp.jam flags xlcpp.compile.c++ OPTIONS <cxxstd>11 : -std=c++11 ; Can you update the xlcpp.jam file to support the cxxstd=11 option, similar to what is implemented in pgi.jam? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Roy Musselman IBM HPC Application Analyst at Lawrence Livermore National Lab email: roymuss(a)us.ibm.com

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[asio] writing composed operations example
by Stephan Menzel 02 Sep '19

02 Sep '19

Hi everyone, as a long time asio user I often had needs to wrap up repeating patterns of async calls for re-use. Normally I went for some kind of specialized object that wraps smaller pieces but I recently came across a series of examples which try to explain how own composed operations may be created. https://www.boost.org/doc/libs/1_71_0/doc/html/boost_asio/examples/cpp11_ex… Now, looking at the examples they are of course way over my head but since own composed operations would be very much exactly what I need I thought I'd give it a shot. But as I now look at this example here: https://www.boost.org/doc/libs/1_71_0/doc/html/boost_asio/example/cpp11/ope… I notice something that I hope somebody can explain. In the coroutine implementation it says: delay_timer_->expires_after(std::chrono::seconds(1)); yield delay_timer_->async_wait(std::move(self)); if (error) break; yield boost::asio::async_write(socket_, boost::asio::buffer(*encoded_message_), std::move(self)); I'm puzzled about the double std::move() of self. In the comments above it says that self is a reference to an intermediate completion handler. How can this be moved twice? Can anyone give me hint about what this means? I would also appreciate any hints in general about own composed operations. Perhaps there are other approaches that are a bit less intimidating? Cheers, Stephan

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