This is my first time at Meeting C++ in Berlin. I came here with my boss Andi. To profit more, we split up during the talks. Afterwards we shared what we learned.
I will complete this post later, and add links to the presentations and videos as they become available.
I attended the following talks:
Opening Keynote by Bjarne Stroustrup
He talked about the evolution and future direction of C++. Explaining the guiding principles and philosophy of the language. He also explained how the standards committee works, and that even he himself is sometimes over voted. He could tell that and even name the people of other opinions without any bitterness. Very professional and focused!
The main point that sticked out was: “zero overhead abstractions”
Unfortunately Peter Sommerlad was sick and couldn’t come. So Bjarne Stroustrup agreed ten minutes before his own keynote to jump in, and give the talk without any preparation. He claimed never to have had a talk about this topic. He had some slides with the name of his employer, and he jumped around in those slides. Other than this barely noticeable detail, you couldn’t tell that the talk was not prepared. He talked about how to use the [GSL](https://github.com/Microsoft/GSL) in new code. But the main focus was on how to gradually improve old legacy code by introducing the types the GSL provides. In the future there should be even tools to perform the task automatically.
He started out by showing how fold can be performed at runtime with std::accumulate(). Then he gave some theory and showed the syntax of other languages such as: haskell, python and scala. The C++17 fold expression operator doesn’t just add syntactic sugar, but open up a load of new possibilities. With constexpr functions, the folds can be evaluated at compile time. As a consequence they can not only operate on values, but even on types. The talker shared with us how he broke his personal error message record: During his experiments he got an error with a quarter of a million lines!
In this talk we witnessed how a relatively simple game can be implemented with help of the following libraries: ranges, dependency injection and state machine. The code was all in pure C++14 and was then compiled to asm.js and/or webassembly using emscripten. The result was a static website that runs the game very efficiently in the browser. In the talk we were walked through the different parts of the implementation. In contrast to a naive imperative approach, after the initial learning curve this can be maintained and extended a lot easier.
We didn’t actually learn how to program robots. First, she walked us through some history of robotics. By highlighting some of the mayor challenges, she explained different solutions, and how they evolved over time. Because robots run in a real time environment and have lots of data to process, performance is crucial. In the past the problems were solved more analytically, while nowadays the focus is on deep learning with neuronal networks. She had a strong emphasis on libraries that are being used in robotics. To my surprise, I knew and used most of them, even the ones she introduced as lesser known such as dlib.
In the evening there was free beer in the big underground hall. There was no music, so that people could talk. Not really how you would usually imagine a party. We had a look at the different sponsor booths, and watched some product demos. After a while we went up to the sky lounge in the 14th floor with a marvelous view over the city.
Even though I experimented with heterogeneous parallel computing a few years ago, I was not really aware what is in the works with SYCL. My earlier experiments were with OpenCL and Cuda. They were cool, but left a lot to be desired. I never looked into OpenAMP despite the improved syntax. In Contrast SYCL seems to do it right on all fronts. I hope this brings GPGUP within reach, so that I could use it in my day to day work sometimes. In the talk, he showed the general architecture, how the pipelines work. Rather than defining execution barriers yourself and schedule the work, you define work groups, and their dependencies. SYCL then figures out how to best arrange and schedule the different tasks onto the different cores. Finally he talked about higher level libraries where SYCL is being integrated: std parallel algorithms, tensor flow and computer vision.
During this talk we learned how static analyzers find the potential problems in the code to warn the developers about. Starting with simple semantic searches, through path tracing with and without branch merging. Bottom line was that there is no one tool to beat them all, but that the more tools you use, the better. Because they all work differently, each on can find individual problems.
This talk made me realize how long ago it was, that I learned about hardware architectures in school. Back in the day we thought mainly about the simple theoretical model of how an ALU works. The talk made clear how you could boost performance by distributing the work to the different parallel ALU’s that exist within every CPU core. In the example he boosted the performance by two simply by manually partially unroll a summation loop. Another important point to take home is the performance gap between CPU and memory access. Even for caches, it is widening with every new hardware generation. Traditional algorithm analysis considers floating point operations as the expensive part. But meanwhile you can execute hundreds of FLOP’s in the time it takes to resolve a single cache miss. On one side he showed some techniques to better utilize the available hardware. And on the other hand he demonstrated tools to measure different aspects, such as usage of the parallel components within the core, or cache misses. With so diverse hardware it is really difficult to predict, thus measuring is key.
The short talks were of varying quality, but mostly funny. As with a good portion of the talks, there were technical difficulties with connecting the notebooks to the projectors.
Closing keynote by Louis Dionne
C++ metaprogramming: evolution and future directions
We both didn’t know what to expect from this talk. But it proved to be one of the best of the conference. He started out by showing some template meta programming with the boost::mpl, transitioned to boost::fusion, and landed at his hana library. The syntax for C++ TMP is generally considered insane. But with his hana library, types are treated like values. This makes the compile time code really readable and only distinguishable from runtime code at a second glance. True to the main C++ paradigm of zero overhead abstraction he showcased an implementation of an event dispatcher that looks like runtime code with a map, but actually resolves at compile time to direct function calls. Cool stuff really. Leveraging knowledge that is available at compile time and use it at compile time. He even claimed that in contrast to some other TMP techniques, compile times should not suffer so much with hana.
C++ is fancy again!
I have been programming professionally for about 17 years. In all this time C++ has been my primary language. Not only that, it has also always been my preferred language. But there were times where it seemed to be stagnating. Other languages had fancy new features. They claimed to catch up with C++ performance. But experience showed that none ever managed to run as fast as C++ or produced such a small footprint. The fancy features proved either not as useful as they first appeared, or they are being added to C++. In retrospect it seems to have been the right choice to resist the urge to add a garbage collector. It’s better to produce no garbage in the first place. RAII turns out to be the better idiom as it can be applied to all sorts of resources, not only memory. The pace with which the language improves is only accelerating.
Yes, there is old ugly code that is using dangerous features. That is how the language evolved, and we can’t get rid of it. But with tools like the GSL and static analyzers we still can improve the security of legacy code bases.