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Does memory leak? (1995)

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Re: Does memory leak? (1995)

#221

Post by jakeinspace »

bargle0 wrote: post #210
0xffff2 wrote: post #91

Earlier quoted context omitted.

The embedded world is very slow to change, so you can read about "modern approaches" (i.e. approaches used today) in any book about embedded programming written in the last 30 years. I currently work on spacecraft flight software and the only real advance on this project over something like the space shuttle that I can point to is that we're trying out some continuous integration on this project. We would like to use…

How do you do CI/CD for embedded systems?

CI during the first phases of development in my experience is now often done with modern tooling (gitlab CI, Jenkins), compiling and running tests on a regular Linux x86 build server. Later phases switch over to some sort of emulated test harness, with interrupts coming from simulated flight hardware. Obviously the further along in the development process, the more expensive and slow it is to run tests. Maybe some software groups (SpaceX?) have a process that allows for tight test loops all the way to actual hardware in the loop tests.

Re: Does memory leak? (1995)

#222

Post by DavidVoid »

dahart wrote: post #115
GordonS wrote: post #42

A bit OT, but I wonder how I'd feel if I was offered a job working on software for missiles. I'm sure the technical challenge would be immensely interesting, and I could tell myself that I cared more about accuracy and correctness than other potential hires... but from a moral standpoint, I don't think I could bring myself to do it. I realise of course that the military uses all sorts of software, including line of b…

I had a family friend who worked on missiles and drones and other defense systems. He was really one of my dad’s running buddies, and he was a super nice guy, had 4 kids, went to church, etc. One day, I believe during the Iraq occupation, maybe ~12 or 13 years ago, I asked him very directly how he felt about working on these killing machines and whether it bothered him. He smiled and asked if I’d rather have the war…

> New technology, he truly believed was preventing innocent civilians from being killed.

Drones and missiles are definitely a step forward compared to previous technology in many regards, but I can't help but be reminded of people who argued that the development and use of napalm would reduce human suffering by putting an end to the war in Vietnam faster.

For an interesting and rather nuanced (but not 100% realistic) view on drone strikes, I'd recommend giving the 2015 movie Eye in the Sky a watch.

Another issue with drone strikes and missiles is "the bravery of being out of range": it's easier to make the decision to kill someone who you're just watching on a screen than it is to look a person in the eyes and decide to have them killed.

Re: Does memory leak? (1995)

#223

Post by hyldmo »

bargle0 wrote: post #210
0xffff2 wrote: post #91

Earlier quoted context omitted.

The embedded world is very slow to change, so you can read about "modern approaches" (i.e. approaches used today) in any book about embedded programming written in the last 30 years. I currently work on spacecraft flight software and the only real advance on this project over something like the space shuttle that I can point to is that we're trying out some continuous integration on this project. We would like to use…

How do you do CI/CD for embedded systems?

I can't speak for what the rest of the industry does, but some chip manufacturers provide decent emulators, so you can run some tests there. We have also done some hardware tests where we connect our hardware to a raspberry pi or similar and run our CI there. It doesn't replace real-world testing, but it does get us some of the way there.

Re: Does memory leak? (1995)

#224

Post by lmilcin »

I once worked on an application which if failed even once meant considerable loss for the company including possible closure.

By design, there was no memory management. The memory was only ever allocated at the start and never de-allocated. All algorithms were implemented around the concept of everything being a static buffer of infinite lifetime.

It was not possible to spring a memory leak.

Re: Does memory leak? (1995)

#225

Post by conro1108 »

lmilcin wrote: post #224

I once worked on an application which if failed even once meant considerable loss for the company including possible closure. By design, there was no memory management. The memory was only ever allocated at the start and never de-allocated. All algorithms were implemented around the concept of everything being a static buffer of infinite lifetime. It was not possible to spring a memory leak.

This sounds fascinating, could you elaborate any on why a single failure of this application would be so catastrophic?

Re: Does memory leak? (1995)

#226

Post by a1369209993 »

wallacoloo wrote: post #174
AtlasBarfed wrote: post #145

Earlier quoted context omitted.

You're advocating throwing baby out with bathwater. Rust interops with C seamlessly, doesn't it? You don't have to throw out good code to use a better language or framework. C may be statically analyzable to some degree, but if Rust's multithreading is truly provable, then new code can be Rust and of course still use the tried and true C libraries. Disclaimer: I still haven't actually learned any Rust, so my logic is…

> Rust interops with C seamlessly, doesn't it? From someone who works in a mixed C + Rust codebase daily (Something like 2-3M lines of C and 100k lines of Rust), yes and no. They're pretty much ABI compatible, so it's trivial to make calls across the FFI boundary. But each language has its own set of different guarantees it provides and assumes , so it's easy to violate one of those guarantees when crossing a FFI bou…

> On the rust side, it's that, plus the pointer must point to a valid region of memory (non-null) even if the slice is empty.

Do you have a citation for that, because it seems obviously wrong[0] (since the slice points to zero bytes of memory) and I'm having trouble coming up with any situation that would justify it (except possibly using a NULL pointer to indicate the Nothing case of a Maybe datum)?

0: by which I mean that Rust is wrong to require that, not that you're wrong about what Rust requires.

Re: Does memory leak? (1995)

#227

Post by lmilcin »

conro1108 wrote: post #225
lmilcin wrote: post #224

I once worked on an application which if failed even once meant considerable loss for the company including possible closure. By design, there was no memory management. The memory was only ever allocated at the start and never de-allocated. All algorithms were implemented around the concept of everything being a static buffer of infinite lifetime. It was not possible to spring a memory leak.

This sounds fascinating, could you elaborate any on why a single failure of this application would be so catastrophic?

I can't discuss this particular application.

But there are whole classes of applications that are also mission critical -- an example might be software driving your car or operating dangerous chemical processes.

For automotive industry there are MISRA standards which we used to guide our development process amongst other ideas from NASA and Boeing (yeah, I know... it was some time ago)

Re: Does memory leak? (1995)

#228

Post by foota »

monocasa wrote: post #170
dahart wrote: post #141

Earlier quoted context omitted.

The games and GPU apps I’ve worked on use memory pools for small allocations, where there will be individual pools for all, say, 1-16 byte allocations, 16-64 byte allocations, 64-256 byte allocations, etc. (Sizes just for illustration, not necessarily realistic). The pool sizes always get tuned over time to match the approximate high water mark of the application. I think pools and arenas mean pretty much the same th…

I've seen Jason Gregory talk about per frame arenas in Game Engine Architecture as a fundamental piece of how the Naughty Dog engines tend to work. Totally agreed that they aren't required for shipping great console games (and they're really hard to use effectively in C++ since you're pretty much guaranteed to have hanging references if you don't have ascetic levels of discipline). This is mainly just meant as a "her…

Seems like this could be handled with a wrapper type with runtime checks during debug?

Like make any pointer to the per frame allocation be a TempPointer or something and then assert they're all gone with a static count variable of them? Then you just have to be cautious whenever you pass a reference to one or convert to a raw pointer.

I don't think this would be too awful for performance in debug builds.

Re: Does memory leak? (1995)

#229

Post by djsumdog »

My undergraduate mentor took a co-op position one year in Huntsville, Alabama. He told me about 6 processor missile guidance systems that cost tens of thousands of dollars ... all to guide a missile to where it gets blown up.

Re: Does memory leak? (1995)

#230

Post by rowanG077 »

amw-zero wrote: post #106
rowanG077 wrote: post #97

Earlier quoted context omitted.

I find it interesting that such critical code is written in C. Why not use something with a lot more (easily)statically provable properties. Like Rust or Agda?

You’ll find that for very serious, industrial applications, a conservative mindset prevails. C may not be trendy at the moment, but it powers the computing world. Its shortcomings are also extremely well known and also statically analyzable. Also, think about when flight software started being written. Was Rust an option? And once it came out, do you expect that programmers who are responsible for millions of people’…

Ada has existed for 40 years. This directly means it has nothing to do with being conservative.
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