CppCon 2019 Trip Report and Slides

Having been back from CppCon 2019 for over a week, I thought it was about time I wrote up my trip report.

The venue

This year, CppCon was at a new venue: the Gaylord Rockies Resort near Denver, Colorado, USA. This is a huge conference centre, currently surrounded by vast tracts of empty space, though people told me there were many plans for developing the surrounding area.

There were hosting multiple conferences and events alongside CppCon; it was quite amusing to emerge from the conference rooms and find oneself surrounded by people in ballgowns and fancy evening wear for an event in the nearby ballroom!

There were a choice of eating establishments, but they all had one thing in common: they were overpriced, taking advantage of the captured nature of the hotel clientelle. The food was reasonably nice though.

The size of the venue did make for a fair amount of walking around between sessions.

Overall the venue was nice, and the staff were friendly and helpful.

Pre-conference Workshop

I ran a 2-day pre-conference class, entitled More Concurrent Thinking in C++: Beyond the Basics, which was for those looking to move beyond the basics of threads and locks to the next level: high level library and application design, as well as lock-free programming with atomics. This was well attended, and I had interesting discussions with people over lunch and in the evening.

If you would like to book this course for your company, please see my training page.

The main conference

Bjarne Stroustrup kicked off the main conference with his presentation on "C++20: C++ at 40". Bjarne again reiterated his vision for C++, and outlined some of the many nice language and library features we have to make development easier, and code clearer and less error-prone.

Matt Godbolt's presentation on "Compiler Explorer: Behind the Scenes" was good and entertaining. Matt showed how he'd evolved Compiler Explorer from a simple script to the current website, and demonstrated some nifty things about it along the way, including features you might not have known about such as the LLVM instruction cost view, or the new "run your code" facility.

In "If You Can't Open It, You Don't Own It", Matt Butler talked about security and trust, and how bad things can happen if something you trust is compromised. Mostly this was obvious if you thought about it, but not something we necessarily do think about, so it was nice to be reminded, especially with the concrete examples. His advice on what we can do to build more secure systems, and existing and proposed C++ features that help was also good.

Barbara Geller and Ansel Sermersheim made an enthusiastic duo presenting "High performance graphics and text rendering on the GPU for any C++ application". I am excited about the potential for their Copperspice wrapper for the Vulkan rendering library: rendering 3D graphics portably is hard, and text more so.

Andrew Sutton's presentation on "Reflections: Compile-time Introspection of Source Code" was an interesting end to Monday. There is a lot of scope for eliminating boilerplate if we can use reflection, so it is good to see the progress being made on it.

Tuesday morning began with a scary question posed by Michael Wong, Paul McKenney and Maged Michael: "Will Your Code Survive the Attack of the Zombie Pointers?" Currently, if you delete an object or call free then all copies of those pointers immediately become invalid across all threads. Since invalid pointers can't even be compared, this can result in zombies eating your brains. Michael, Paul and Maged looked at what we can do in our code to avoid this, and what they are proposing for the C++ Standard to fix the problem.

Andrei Alexandrescu's presentation on "Speed is found in the minds of people" was an insightful look at optimizing sort. Andrei showed how compiler and processor features mean that performance can be counter-intuitive, and code with a higher algorithmic complexity can run faster in the right conditions. Always use infinite loops (except for most cases).

I love the interactive slides in Hana Dusikova's presentation "A State of Compile Time Regular Expressions". She is pushing the boundaries of compile-time coding to make our code perform better at runtime. std::regex can be slow compared to other regular expression libraries, but ctre can be much better. I am excited to see how this can be extended to compile-time parsing of other DSLs.

In "Applied WebAssembly: Compiling and Running C++ in Your Web Browser", Ben Smith showed the use of WebAssembly as a target to allow you to write high-performance C++ code that will run in a suitable web browser on any platform, much like the "Write once, run anywhere" promise of Java. I am interested to see where this can lead.

Samy Al Bahra and Paul Khuong presented the final session I attended: "Abusing Your Memory Model for Fun and Profit". They discussed how they have written code that relies on the stronger memory ordering requirements imposed by X86 CPUs over and above the standard C++ memory model in order to write high-performance concurrent data structures. I am intrigued to see if any of their techniques can be used in a portable fashion, or used to improve Just::Thread Pro.

Whiteboard code

This year there were a few whiteboards around the conference area for people to use for impromptu discussions. One of them had a challenge written on it:

"Can you write a requires expression that ensures a class has a member function with a specified signature?"

This led to a lot of discussion, which Arthur O'Dwyer wrote up as a blog post. Though the premise of the question is wrong (we shouldn't want to constrain on such specifics), it was fun, interesting and enlightening trying to think how one might do it — it allows you to explore the corner cases of the language in ways that might turn out to be useful later.

My presentation

As well as the workshop, I presented a talk on "Concurrency in C++20 and beyond", which was on Tuesday afternoon. It was in an intermediate-sized room, and I believe was well attended, though it was hard to see the audience with the bright stage lighting. There were a number of interesting questions from the audience addressing the issues raised in my presentation, which is always good, though the acoustics did make it hard to hear some of them.

Slides are available here.

~trip_report()

So that was an overview of another awesome CppCon. I love the in-person interactions with so many people involved in using C++ for such a wide variety of things. Everyone has their own perspective, and I always learn something.

The videos are being uploaded incrementally to the CppCon YouTube channel, so hopefully the video of my presentation and the ones above that aren't already available will be uploaded soon.

Posted by Anthony Williams
[/ news /] permanent link
Tags: , , , , , ,
Stumble It! stumbleupon logo | Submit to Reddit reddit logo | Submit to DZone dzone logo

Comment on this post

Follow me on Twitter

A zero-knowledge proofs workshop

I was at the Zero-Knowledge proofs workshop run by BinaryDistict on Monday and Tuesday. The workshop runs all week, but is mostly hacking for the remaining days (hacking would be interesting if I had a problem to code, more about this at the end).

Zero-knowledge proofs allow person A to convince person B, that A knows the value of x, without revealing the value of x. There are two kinds of zero-knowledge proofs: an interacting proof system involves a sequence of messages being exchanged between the two parties, and in non-interactive systems (the primary focus of the workshop), there is no interaction.

The example usually given, of a zero-knowledge proof, involves Peggy and Victor. Peggy wants to convince Victor that she knows how to unlock the door dividing a looping path through a tunnel in a cave.

The ‘proof’ involves Peggy walking, unseen by Victor, down path A or B (see diagram below; image from Wikipedia). Once Peggy is out of view, Victor randomly shouts out A or B; Peggy then has to walk out of the tunnel using the path Victor shouted; there is a 50% chance that Peggy happened to choose the path selected by Victor. The proof is iterative; at the end of each iteration, Victor’s uncertainty of Peggy’s claim of being able to open the door is reduced by 50%. Victor has to iterate until he is sufficiently satisfied that Peggy knows how to open the door.

Alibaba example cave loop.

As the name suggests, non-interactive proofs do not involve any message passing; in the common reference string model, a string of symbols, generated by person making the claim of knowledge, is encoded in such a way that it can be used by third-parties to verify the claim of knowledge. At the workshop we got an overview of zk-SNARKs (zero-knowledge succinct non-interactive argument of knowledge).

The ‘succinct’ component of zk-SNARK is what has made this approach practical. When non-interactive proofs were first proposed, the arguments of knowledge contained around one-terabyte of data; these days common reference strings are around a kilobyte.

The fact that zero-knowledge ‘proof’s are possible is very interesting, but do they have practical uses?

The hackathon aspect of the workshop was designed to address the practical use issue. The existing zero-knowledge proofs tend to involve the use of prime numbers, or the factors of very large numbers (as might be expected of a proof system that was heavily based on cryptography). Making use of zero-knowledge proofs requires mapping the problem to a form that has a known solution; this is very hard. Existing applications involve cryptography and block-chains (Zcash is a cryptocurrency that has an option that provides privacy via zero-knowledge proofs), both heavy users of number theory.

The workshop introduced us to two languages, which could be used for writing zero-knowledge applications; ZoKrates and snarky. The weekend before the workshop, I tried to install both languages: ZoKrates installed quickly and painlessly, while I could not get snarky installed (I was old that the first two hours of the snarky workshop were spent getting installs to work); I also noticed that ZoKrates had greater presence than snarky on the web, in the form of pages discussing the language. It seemed to me that ZoKrates was the market leader. The workshop presenters included people involved with both languages; Jacob Eberhardt (one of the people behind ZoKrates) gave a great presentation, and had good slides. Team ZoKrates is clearly the one to watch.

As an experienced hack attendee, I was ready with an interesting problem to solve. After I explained the problem to those opting to use ZoKrates, somebody suggested that oblivious transfer could be used to solve my problem (and indeed, 1-out-of-n oblivious transfer does offer the required functionality).

My problem was: Let’s say I have three software products, the customer has a copy of all three products, and is willing to pay the license fee to use one of these products. However, the customer does not want me to know which of the three products they are using. How can I send them a product specific license key, without knowing which product they are going to use? Oblivious transfer involves a sequence of message exchanges (each exchange involves three messages, one for each product) with the final exchange requiring that I send three messages, each containing a separate product key (one for each product); the customer can only successfully decode the product-specific message they had selected earlier in the process (decoding the other two messages produces random characters, i.e., no product key).

Like most hackathons, problem ideas were somewhat contrived (a few people wanted to delve further into the technical details). I could not find an interesting team to join, and left them to it for the rest of the week.

There were 50-60 people on the first day, and 30-40 on the second. Many of the people I spoke to were recent graduates, and half of the speakers were doing or had just completed PhDs; the field is completely new. If zero-knowledge proofs take off, decisions made over the next year or two by the people at this workshop will impact the path the field follows. Otherwise, nothing happens, and a bunch of people will have interesting memories about stuff they dabbled in, when young.

Is it worth attending an academic conference or workshop?

If you work in industry, is it worth attending an academic conference or workshop?

The following observations are based on my attending around 50 software engineering and compiler related conferences/workshops, plus discussion with a few other people from industry who have attended such events.

Short answer: No.

Slightly longer answer: Perhaps, if you are looking to hire somebody knowledgeable in a particular domain.

Much longer answer: Academics go to conferences to network. They are looking for future collaborators, funding, jobs, and general gossip. What is the point of talking to somebody from industry? Academics will make small talk and be generally friendly, but they don’t know how to interact, at the professional level, with people from industry.

Why are academics generally hopeless at interacting, at the professional level, with people from industry?

Part of the problem is lack of practice, many academic researchers live in a world that rarely intersects with people from industry.

Impostor syndrome is another. I have noticed that academics often think that people in industry have a much better understanding of the realities of their field. Those who have had more contact with people from industry might have noticed that impostor syndrome is not limited to academia.

Talking of impostor syndrome, and feeling of being a fraud, academics don’t seem to know how to handle direct criticism. Again I think it is a matter of practice. Industry does not operate according to: I won’t laugh at your idea, if you don’t laugh at mine, which means people within industry are practiced at ‘robust’ discussion (this does not mean they like it, and being good at handling such discussions smooths the path into management).

At the other end of the impostor spectrum, some academics really do regard people working in industry as simpletons. I regularly have academics express surprise that somebody in industry, i.e., me, knows about this-that-or-the-other. My standard reply is to say that its because I paid more for my degree and did not have the usual labotomy before graduating. Not a reply guaranteed to improve industry/academic relations, but I enjoy the look on their faces (and I don’t expect they express that opinion again to anyone else from industry).

The other reason why I don’t recommend attending academic conferences/workshops, is that lots of background knowledge is needed to understand what is being said. There is no point attending ‘cold’, you will not understand what is being presented (academic presentations tend to be much better organized than those given by people in industry, so don’t blame the speaker). Lots of reading is required. The point of attending is to talk to people, which means knowing something about the current state of research in their area of interest. Attending simply to learn something about a new topic is a very poor use of time (unless the purpose is to burnish your c.v.).

Why do I continue to attend conferences/workshops?

If a conference/workshop looks like it will be attended by people who I will find interesting, and it’s not too much hassle to attend, then I’m willing to go in search of gold nuggets. One gold nugget per day is a good return on investment.

CppCon 2017 class and presentation on concurrency

I am pleased to announce that I will be running my "Concurrent Thinking in C++" class at CppCon again this year. Here is the course description:

One of the most difficult issues around designing software with multiple threads of execution is synchronizing data.

Whether you use actors, active objects, futures and continuations or mutable shared state, every non-trivial system with multiple threads needs to transfer data between them. This means thinking about which data needs to be processed by which thread, and ensuring that the right data gets to the right threads in the right order. It also means thinking about API design to avoid race conditions.

In this workshop you will encounter a series of scenarios involving multithreaded code, and be guided through identifying the problem areas and the ways of handling them.

You will learn techniques for thinking about the scenarios to ease the analysis, as well as details of the tools we have available in C++ to mitigate the problems. You will also learn how to use the C++ standard library to help enforce the requirements of each scenario in code.

I will also be presenting on "Concurrency, Parallelism and Coroutines":

C++17 is adding parallel overloads of most of the Standard Library algorithms. There is a TS for Concurrency in C++ already published, and a TS for Coroutines in C++ and a second TS for Concurrency in C++ in the works.

What does all this mean for programmers? How are they all related? How do coroutines help with parallelism?

This session will attempt to answer these questions and more. We will look at the implementation of parallel algorithms, and how continuations, coroutines and work-stealing fit together. We will also look at how this meshes with the Grand Unified Executors Proposal, and how you will be able to take advantage of all this as an application developer.

My class is on 17th-18th September, and the main conference is running 19th-23rd, with my presentation on 20th September. If you haven't got your ticket already, head on over to CppCon Registration to get yours now.

Hope to see you there!

Posted by Anthony Williams
[/ news /] permanent link
Tags: , , , ,

| Stumble It! stumbleupon logo | Submit to Reddit reddit logo | Submit to DZone dzone logo

Comment on this post

Follow me on Twitter