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Does memory leak? (1995)

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Re: Does memory leak? (1995)

#121

Post by enriquto »

giu wrote: post #85
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.

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…

> 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?

The JPL coding guidelines for C [1] are an amusing, first-hand read about this stuff. Not sure if you would qualify them as "modern approaches".

[1] https://en.wikipedia.org/wiki/The_Power_of_10:_Rules_for_Dev...

Re: Does memory leak? (1995)

#122

Post by enriquto »

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.

Unless you are an extreme pacifist (which is a perfectly reasonable thing to be), you'll acknowledge the legitimate need for the existence of an army in your country. In that case, the army better be equipped by missiles than by youths carrying bayonets. Then, there's nothing wrong in providing these missiles with technologically advanced guiding systems.

On the other hand, if I worked in "algorithmic trading" or fancy "financial instruments" I would not be able to sleep at night without a fair dose of drugs.

Re: Does memory leak? (1995)

#123

Post by alerighi »

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…

Freeing memory (or running a garbage collector) has a cost associated with it, and if you are freeing memory (or closing files, sockets, etc) before exiting a program it's time wasted, since the OS will free all the resources associated with the program anyway.

And a lot of languages, and for sure newer version of the JVM, do exactly that, they don't free memory, and doesn't run the garbage collector since the available memory gets too low. And that is fine for most applications.

Re: Does memory leak? (1995)

#124

Post by alex_young »

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…

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 question about the moral culpability of working in this area.

Re: Does memory leak? (1995)

#125

Post by needusername »

derefr wrote: post #68

Erlang has a parameter called initial_heap_size. Each new actor-process in Erlang gets its own isolated heap, for which it does its own garbage-collection on its own execution thread. This initial_heap_size parameter determines how large each newly-spawned actor’s heap will be. Why would you tune it? Because, if you set it high enough, then for all your short-lived actors, memory allocation will become a no-op (= bum…

> memory allocation will become a no-op (= bump allocation)

No, that's a cache miss.

Re: Does memory leak? (1995)

#126

Post by BiteCode_dev »

GuB-42 wrote: post #92
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…

There are different kinds of killing machines. And accurate missiles are among the least bad. With the exception of nuclear weapons (that's another topic), missiles are designed to destroy one particular target of strategic importance and nothing more. They are too expensive as mass killing weapons, but they are particularly appropriate for defense. Without missiles, you may need to launch an assault, destroying ever…

On the other hand, making killing a target easier to do gives you the incentive to do just this instead of trying to find an alternative solution.

Case in point: currently the country with the best army in the world is also the one going the most at war.

Re: Does memory leak? (1995)

#127

Post by bdavis__ »

rowanG077 wrote: post #97
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…

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?

Ada is used a fair amount in high $ projects. Toolchains are expensive, and the C compiler is provided for free from the chip / board vendor.

Re: Does memory leak? (1995)

#128

Post by bdavis__ »

bootloop wrote: post #81
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.

I would imagine it might make sense if you offload some short, less frequent but memory intensive sub-routines (sensors, navigation) to run in parallel to the rest of the system. But I would still avoid having a system wide dynamic memory management and just implement one specifically for that part.

when you design the system, you make sure there is enough physical RAM to do the job. Period. the problem space is bounded.

Re: Does memory leak? (1995)

#129

Post by bdavis__ »

H8crilA wrote: post #26
ptero wrote: post #23

Earlier quoted context omitted.

In a perfect world, yes. But in a hard real time system (and much of missile control will likely be designed as such), timing may be the #1 focus. That is, making sure that events are handled in at most X microseconds or N CPU cycles. In such cases adding GC may open a new can of worms. I agree that in general leaking resources is bad, but sometimes it is good enough by a large margin. Just a guess.

It would be an acceptable solution if the memory supply would vastly outsize the demand, by over an order of magnitude. For example if the program never needed more than 100MiB and you'd install 1GiB or 10GiB. 10GiB is still nothing compared to the cost of the missile, and you get the benefit of truly never worrying about the memory management latency. My favorite trick to optimizing some systems is to see if I can m…

there are always constraints. other than the cost of the memory, which may appear minimal, there are many others. for a missile that bigger memory chip may require more current, more current means a bigger power supply, or a thicker wire. might add ounces to the weight. and in this environment, that may be significant (probably not in this specific example, but look at this perspective for every part selected...they sum up)

Re: Does memory leak? (1995)

#130

Post by GordonS »

enriquto wrote: post #122
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. Unless you are an extreme pacifist (which is a perfectly reasonable thing to be), you'll acknowledge the legitimate need for the existence of an army in your country. In that case, the army better be equipped by missiles than by youths carrying bayonets. Then, there's nothing wrong in providing these missiles with technolog…

It's not that I'm a pacifist, but more that I don't trust my government (UK, but I have the same issues with the US gov too) to do justifiable things with them.

If they were for defense only, I might be able to do it. But instead they are sold to any government with the means to pay, regardless of their human rights record or how they will be used (e.g. Saudi). Aside from selling them on, they are used in conflicts that are hard to justify, beyond filling the coffers of the rich and powerful. Take the latest Iraq war for example: started based on falsified evidence, hundreds of thousands dead, atrocities carried out by the west, schools bombed, incidents covered up...

Given these realities, I just couldn't do it.

My original musing was more thinking along the lines of an ideal world, where I trusted my government; I'm still not sure I could do it.

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