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Does memory leak? (1995)

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Re: Does memory leak? (1995)

#201

Post by samatman »

alex_young wrote: post #124
dahart wrote: post #115

Earlier quoted context omitted.

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…

Costa Rica hasn’t had a standing military since 1948. They are in one of the most politically unstable parts of the world and do just fine without worry of invasion. The US hasn’t been attacked militarily on its own soil in the modern era. The US military monopoly hasn’t prevented horrific attacks such as 9/11 executed by groups claiming to be motivated by our foreign military campaigns. I think there is a valid ques…

In practice, Costa Rica has a standing military. It's just the US military.

Due to the Monroe Doctrine, this is a rational stance for Costa Rica to take. If the US were to adopt this policy, Costa Rica might have to take a hard look at repealing it.

Re: Does memory leak? (1995)

#202

Post by samatman »

simias wrote: post #13

I think it's a bad mindset to leak resources even when it doesn't effectively matter. In non-garbage collected languages especially, because it's important to keep in mind who owns what and for how long. It also makes refactoring easier because leaked resources effectively become some sort of implicit global state you need to keep track of. If a function that was originally called only once at startup is not called r…

There are a number of old-school C programs that follow a familiar template: they're invoked on the command line, run from top to bottom, and exit.

For those, it's often the case that they allocate-only, and have a cleanup block for resources like file handles which must be cleaned up; any error longjmps there, and it runs at the end under normal circumstances.

This is basically using the operating system as the garbage collector, and it works fine.

Re: Does memory leak? (1995)

#203

Post by samatman »

MrBuddyCasino wrote: post #15

Why go through the trouble of a) calculating maximum leakage b) doubling physical memory instead of just fixing the leaks? Was it to save cycles? Prevent memory fragmentation? I feel this story misses the details that would make it more than just a cute anecdote.

It's a missile.

The memory is going to fragment no matter what you do.

Re: Does memory leak? (1995)

#204

Post by Filligree »

saagarjha wrote: post #87
sumanthvepa wrote: post #20

Earlier quoted context omitted.

I used to work at Amazon the late 90s and this was the policy they followed. The apache server module written in C would leak so much that the process would have to be killed every 10 requests. The problem with the strategy was that it required a lot of CPU and RAM to startup a new process. Amazons answer was to simply throw hardware at the problem. Growing the company fast was more important than cleaning up RAM. Th…

> The problem with the strategy was that it required a lot of CPU and RAM to startup a new process. It's not really kosher, but why not just keep around a fresh process that they can continually fork new handlers from?

Setting it up was expensive, so there's a good chance it involved initializing libraries, launching threads, or otherwise creating state that isn't handled correctly by fork.

Re: Does memory leak? (1995)

#205

Post by dodobirdlord »

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’…

> Also, think about when flight software started being written. Was Rust an option?

It wasn't, but Ada probably was (some flight software may have been written before 1980?), and would likely also be a much better choice.

Re: Does memory leak? (1995)

#206

Post by MaxBarraclough »

On such systems the same approach can be taken for a cooling solution. If the chip will fatally overheat in 60 seconds but the device's lifetime is only 45, there's no need for a more elaborate cooling solution.

The always-leak approach to memory management can also be used in short-lived application code. The D compiler once used this approach [0] (I'm not sure whether it still does).

[0] https://www.drdobbs.com/cpp/increasing-compiler-speed-by-ove...

Re: Does memory leak? (1995)

#207

Post by jmpman »

Twirrim wrote: post #191
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…

> A bit OT, but I wonder how I'd feel if I was offered a job working on software for missiles. At one stage in my career I had an opportunity to go work for Betfair. I knew several people there and could bypass most or all of the interview process. At the time a rapidly growing on-line gambling company, wasn't quite the major company it is now. They were paying about half as much again over my existing salary, and te…

The reality behind corporate casinos is a bit more disheartening. Using analytics, from their “players club” cards, they know what zip code you’re from, and based upon that, they approximate your income. They know that if you lose too much, then your wife isn’t going to allow you to return to Vegas. Each income level has a certain pain threshold for how much you can lose in a year. The casino’s work very hard to ensure you don’t go over that limit.

If you’re on a bad losing streak, they’ll send a host over to offer you tickets to a show or a buffet. The goal is to get you AWAY from gambling. They know you’re an addict, but want to keep the addiction going.

That’s where they cross the ethical line.

Re: Does memory leak? (1995)

#208

Post by p_l »

amelius wrote: post #135
giu wrote: post #85

Earlier quoted context omitted.

I'm always fascinated about software running on hardware-restricted systems like planes, space shuttles, and so on. Where can someone (i.e., in my case a software engineer who's working with Kotlin but has used C++ in his past) read more about modern approaches to writing embedded software for such systems? I'm asking for one because I'm curious by nature and additionally because I simply take the garbage collector f…

Just read docs that were written in the 70s, before the advent of garbage collection.

Garbage Collection is from 1959, though - and Unix & C's original model pretty much matches "bump allocate then die" with sbrk/brk and lack of support for moving.

Fully static allocation is the norm though for most "small" embedded work.

Re: Does memory leak? (1995)

#209

Post by p_l »

onceUponADime wrote: post #166
jakeinspace wrote: post #69

As somebody working on embedded software for aerospace, I'm surprised this missile system even had dynamic memory allocation. My entire organization keeps flight-critical code fully statically allocated.

DO 187A ?

DO-178C, actually, but good pointer.

Re: Does memory leak? (1995)

#210

Post by bargle0 »

0xffff2 wrote: post #91
giu wrote: post #85

Earlier quoted context omitted.

I'm always fascinated about software running on hardware-restricted systems like planes, space shuttles, and so on. Where can someone (i.e., in my case a software engineer who's working with Kotlin but has used C++ in his past) read more about modern approaches to writing embedded software for such systems? I'm asking for one because I'm curious by nature and additionally because I simply take the garbage collector f…

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?
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