My visit to Meeting C++ 2016!

Finally, I was able to attend this conference, missing out two years in a row, and it was great. So far it has been the largest yet with 600 attendees, and AFAIK Bjarne Stroustrup was present for the first time this year.

I went to Berlin with my girlfriend two days before the event so we had a chance to see Berlin. Even though the weather was very much what you would expect around this time of year, cloudy, rainy, etc. we had a great time. Especially renting bikes and sightseeing.

Talks I attended... DAY 1

Opening Keynote - Bjarne Stroustrup

What is C++ and what will it become? It was a nice presentation showing the strength of C++ and providing a little history here and there (like code below). Funny quote from the presentation "Only a computer scientist makes a copy then destroys the original"; The committee has a difficult task, making the C++ language less complex, but the only thing the committee can do is add more to it , but they still succeed (i.e., with auto, constexpr, ..).

int i; // 70's? 
for (i=0; i<10; i++) a[i] = 0;
----------
for (int i=0; i<10; i++) a[i] = 0; // 80's? no declaration outside the for
----------
for (auto &el : a) el = 0; // mistakes like reading out of bounds no longer possible
                           // ... also mistakes like; for (int i=0; i<10; j++) {}

Boris Schäling asked "Scott Meyers retired from C++ a year ago; do we need to be worried about you?", luckily we don't have to worry ;-). Bjarne answered that he tried a few times to quit C++ in the past, but apparently he is not very good at it .

Learning and teaching Modern C++ - Arne Mertz

The speaker made an interesting point regarding some pitfalls, i.e. that many C++ developers learned C first, pointers, pointer arithmetic, C++03, C++11, .., basically a "layered evolution". However Modern C++ isn't a layered evolution, rather it is a "moving target". Nowadays we prefer make_unique, unique_ptr and therefor why not postpone teaching new, delete, new[], delete[], pointer arithmetic etc. when teaching Modern C++? The same goes for C-style arrays, more complex to teach as opposed to std::array.

Actually kind of sad news; there are still schools in some Countries where C++ is taught with Turbo C++ (see this SO question from a few days ago) compiler (which is extremely outdated). Other notes I scribbled down were for me to check "clang tidy" and adding "isocpp.org" to my RSS feeds.

Wouter van OOijen--a professor teaching C++ in the context of embedded devices--made a good point: the order in which material is presented to students is the most difficult thing to get right. In most books on C++ the order doesn't make sense for embedded, that's why he creates his own material.

Implementation of a multithreaded compile-time ECS in C++14 - Vittorio Romeo

This was quite interesting, maybe it was just me but in the beginning of the presentation it wasn't clear to me what an Entity Component System was, it became clear to me during the talk though. He walked us through the implementation, advanced templating, lambdas, bit fiddling, all quite interesting, maybe a bit too much content for one presentation but very impressive stuff. The room temperature during the presentation was extremely hot, making it sometimes difficult to concentrate and the talk went a bit over the scheduled time.

Some stuff I found interesting: the usage of sparse sets, the use of proxy objects to make sure that certain methods of the library cannot be called at the wrong time.

ctx->step([&](auto& proxy)
    {
        // do something with proxy
    });

He went through a large list of features and how they are implemented

Ranges v3 and microcontrollers, a revolution -- Odin Holmes

Quite an awesome talk this one, the speaker is extremely knowledgeable on meta programming and embedded programming. His company works with devices with very little memory (just a few kilobyte) and this talk was very forward looking. There was a crash course regarding limitations for such devices, there is limited stack space, how do exceptions and interrupts play along with it.

He then started with real demo/hello world for such a device and demonstrated how even that small code contained bugs and a lot of boilerplate. The rest of the talk he showed how to improve it, like instead of parsing (dangerously) with scanf (you can overflow the buffer, so you need a "large enough" buffer up-front... "And we all know that coming up with a size for a large enough buffer is easy, right?" ) can be replaced with a statemachine known at compile time. Ranges can be applied to lazy evaluate input, and as a result it would consume only the minimal memory.

C++ Today - The Beast is back - Jon Kalb

Why was C/C++ successful? It was based on proven track record, and not a "pure theoretical language". High-level abstractions at low cost, with a goal of zero-abstraction principle. In other words; not slower than you could do by coding the same feature by hand (i.e., vtables).

If you like a good story and are curious about why there was a big red button on the IBM 360, the reason behind the C++ "Dark ages" (2000 - 2010), where very little seem to happen, then this is the presentation to watch. Spoiler alert: cough Java cough, OOP was the buzzword at the time, it was "almost as fast", computers got faster and faster, we "solved the performance issue"!

Interesting statements I jotted down "Managed code optimizes the wrong thing (ease of programming)", and regarding Java's finally (try {} catch {} finally {}): "finally violates DRY". He then asked the audience a few times what DRY stands for, which is quite funny as some people realize they were indeed repeating themselves, not all as someone else yelled "the opposite of WET" . He also "pulled the age card" when discussing Alexander Stephanov (the author of the STL) "You kids think std::vector grew on trees!".

DAY 2

Functional reactive programming in C++ - Ivan Cukic

Talk of two parts, first functional programming: higher order functions, purity, immutable state. Functional thinking = data transformation. He discussed referential transparency, f.i. replacing any function with its value should produce the same outcome. This can depend on your definition.

int foobar()
{
    std::cout << "Returning 42..." << '\n';
    return 42;
}

Above function when used in int n = foobar(); can be replaced by 42, and the line of code would result in exactly the same thing (n containing 42), however the console output won't be printed. Whether you consider std::cout to count as part of the referential transparency is up to you.

He continued with Object thinking = no getters, ask the object to do it. "Objects tend to become immutable.". I will have to review the presentation to get exactly what was meant by this.

Next: reactive programming, if I am correct this was his definition:

• responds quickly
• resilient to failure
• responsive under workload
• based on message-passing

Note: reacting not replying, i.e., piping Linux shell commands there is only one-way data flow. To conclude, some random notes I made during his talk below.

• He's writing a book on Functional programming in C++
• flatmap from functional programming does [x, a], [y, b, c] -> x, a, y, b, c.
• His talk reminded me to lookup the meaning of placing && behind a member function declaration.

See below for an example from cppreference.com.

#include <iostream>

struct S {
    void f() & { std::cout << "lvalue\n"; }
    void f() &&{ std::cout << "rvalue\n"; }
};

int main(){
    S s;
    s.f();            // prints "lvalue"
    std::move(s).f(); // prints "rvalue"
    S().f();          // prints "rvalue"
}

The Speed Game: Automated Trading Systems in C++ - Carl Cook

This talk was probably one of the most well attended talks at the conference. The room was packed. Coming in slightly late I had to sit down on my knees for the entire talk. Which was worth it, I think I liked this talk most of all I attended. It was just the right mix of super interesting material and practical advice.

Coming from Amsterdam where Automated Trading companies seem to kind of dominate C++, it has always been very mysterious what exactly it is they do. It felt to me like it was basically the first time the veil was lifted a little bit. It's just amazing to hear how far they go in order to get the lowest latency possible. Within the time it takes for light to travel from the ground to the top of the Eiffel tower they can take an order, assess whether it's interesting or not, and place the order... times ten!

// Some practical advice, instead of the following..
if (checkForErrorA)
    handleErrorA();
elseif (checkForErrorB)
    handleErrorB();
elseif (checkForErrorC)
    handleErrorC();
else
    executeHotPath();

// Aim for this..
uint32_t errorFlags;
if (errorFlags)
    handleError(errorFlags);
else
{
    ... hotpath
}

Really interesting talk to watch whenever it comes online, it shows the importance of optimizing hardware, bypassing the kernel completely in the hot path, staying in user space for 100%, this includes network I/O (f.i., OpenOnload), cache warming, beware of signed/unsigned conversions, check the assembly, inplace_function (the speakers proposals, stdext::inplace_function<void(), 32>), benchmarking without the 'observable effect' by observing network packets, and more.

One note regarding Network I/O for example; if you read a lot but very little is interesting to the hot path, you may negatively affect your cache. A solution would be to offload all the reads to a different CPU and cherry-pick only the interesting reads and send them to the "hot" CPU.

Lock-free concurrent toolkit for hazard pointers and RCU - Michael Wong

Well, I was a bit tired at this point, so I cannot do the talk justice with a very thorough summary. Even if I could it's better to watch it from Michael Wong himself, because the slides help a lot in understanding the story.

I did learn a few things, maybe the first lesson for me is to try stay away from all of this.. Still, aside from being super complicated, it's also an interesting topic, and good to know more about. The ABA problem: he had good slides that visualized actually step-by-step the challenge of updating data in a multi-threading situation, having readers while writing to it, all wrapped in a fun story of Schrödingers Cat (and Zoo). Solutions discussed were hazard pointers and RCU (Read Copy Update).

The gains you can get by starting late, having a grace period so you can do multiple updates at the same time are interesting to learn about. Situations where "being lazy" actually pays off!

Lightning talks!

Surprise! They had secret lightning talks planned. To be honest at first I thought it was a bit long to have 1 hour and 40 minutes planned for a Meeting C++ update/review, so this was a nice surprise. My favorite lightning talk was from Michael Caisse reading from the standard as if it were a very exiting story, hilarious. Second James McNellis' "function pointers all the way down" (like "Turtles all the way down", actually Bjarne also had a reference to this in his keynote). The remaining lightning talks were also very good: Michael Wong, Jens Weller, Chandler Carruth, and Bjarne's. The latter on Concepts was quite interesting; "what makes a good concept?" It has to have semantics specifying it, which in practice seems to be an efficient design technique. Quite funny was his "Onion principle" on abstractions (IIRC?), "you peel away layer by layer, and you cry more and more as you go along" . Also Jens talk was really fun, it started with end of the world scenarios, working towards the future C++ standards.

C++ metaprogramming: evolution and future directions - Louis Dionne

The closing keynote was a really clear and relaxed presentation of how meta programming evolved, and in particular how boost::hana did. Again a nice lesson of history where Alexandrescu's Modern C++, boost::mpl, boost::fusion and the like all passed the revue. He showed what you can do with boost::hana at compile-time and runtime. His talk really opened my eyes on using constexpr, integral_constant, differences in meta programming with types and objects, and a lot more. It's amazing what his library can do. He argued the world needs more meta programming, but less template meta programming and concluded by sharing his view for the future.

The conference

There was a fun quiz, with really difficult puzzles (C++ programs) that had to be solved in < 3 minutes each. This was basically similar to peeling Bjarne's Onion.. but in a good way.

Between talks there were lunch-break Meetups planned (each 20 minutes, each had a specific topic). I attended two and my view is that it's a great idea, but the fact people have to come from talks, and leave on time to catch the next one, sometimes caused the time to be way too short (or yourself missing out on a talk because the room is now full).

The organization was super, the drinks and food, especially the second day. The Andel's Hotel is a really good location, the Hotel as well (if you are lucky enough to get a room there). For me it was all really worth the money.

Personally I like to write down a summary for myself, but I hope this blog post was also a fun to read to someone else!