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Does memory leak? (1995)

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Re: Does memory leak? (1995)

#141

Post by dahart »

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…

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 thing. https://en.wikipedia.org/wiki/Memory_pool I’ve mostly heard this discussed in terms of pools, but I wonder if there’s a subtle difference, or if there’s a historical reason arena is popular in some circles and pool in others...?

I haven’t personally see a per-frame heap while working in console games, even though games I’ve worked on probably had one, or something like it. Techniques that I did see and are super-common are fixed maximum-size allocations: just pre-allocate all the memory you’ll ever need for some feature and never let it go; stack allocations sometimes with alloca(); and helper functions/classes that put something on the stack for the lifetime of a particular scope.

Re: Does memory leak? (1995)

#142

Post by dahart »

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.

Note the story isn’t detailed enough to know whether they were using what we’d normally call dynamic memory allocation. The embedded system might not have had a memory manager. Or they might have been, like you, fully statically allocating the memory. Kent could be noting that they’ll run off the end of their statically allocated memory, or run out of address space, because the code isn’t checking the bounds and may be doing something like appending history or sensor data to an array. I have no idea obviously, just imagining multiple ways Kent’s very brief description could be interpreted, it maybe shouldn’t be assumed that the engineering was doing something stupid or even very different from what we’d do today.

Re: Does memory leak? (1995)

#143

Post by asveikau »

LucaSas wrote: post #138

This pops up again from time to time, I think what people should take away from this is that garbage collection is not just what you see in Java and other high level languages. There are a lot of strategies to apply garbage collection and they are often used in low level systems too like per-frame temporary arenas in games or in short lived programs that just allocate and never free.

Once you set a limit like this, though, it's brittle, and your code becomes less maintainable or flexible in the face of change. That is why a general purpose strategy is good to use.

Re: Does memory leak? (1995)

#144

Post by TedDoesntTalk »

saagarjha wrote: post #84
mopsi wrote: post #63

Earlier quoted context omitted.

> 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. Why? The more precise missiles are, the better. If no-one agreed to build missile guidance systems, we'd still have carpet bombing and artillery with 100m accuracy.

People might use them less, though.

How naive. More likely they’d be used just as often, but more civilians would die. See the v1 and v2 nazi rockets, for example, which didn’t have any software.

Re: Does memory leak? (1995)

#145

Post by AtlasBarfed »

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’…

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 CIO-level of potential ignorance.

Re: Does memory leak? (1995)

#146

Post by TedDoesntTalk »

cushychicken wrote: post #57
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 recently interviewed, and was offered a job at, Draper Labs in Cambridge MA. The technical work was super interesting. Everyone I spoke to was plainly super sharp, and not morally bankrupt. I fielded similar moral concerns as you, but truthfully, I don't really have much of a personal ethical problem with it. I was a little more concerned at having to explain it to all of my friends, many of whom are substantially…

First time I’ve heard of someone accepting or not accepting a job based on peer perception. Maybe you should re-evaluate who your peers are if they can’t accept you for your career choices?

Re: Does memory leak? (1995)

#147

Post by AtlasBarfed »

jmpman wrote: post #71
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…

Straight out of college, I was offered a job writing software for missiles. Extremely interesting area, working for my adjunct professor’s team, who I highly admired and whose class was the best of my college career. The pay was on par with all my other offers. I didn’t accept for two reasons. First, I logically agreed that the missiles were supporting our armed services and I believed that our government was general…

> our government was generally on the right side of history

Well, we are the victors, so far. But the war against ourselves is going quite well.

Re: Does memory leak? (1995)

#148

Post by ufo »

blattimwind wrote: post #48
Out_of_Characte wrote: post #37

What an interesting concept. Good programmers always consider certain behaviours to be wrong. Memory 'leaks' being one of them. But this real application of purposefully not managing memory is also an interesting thought exercise. However counter intuitive, a memory leak in this case might be the most optimal solution in this problem space. I just never thought I would have to think of an object's lifetime in such a…

Cleaning up memory is an antipattern for many tools , especially of the EVA/IPO model (input-process-output). For example, cp(1) in preserve hard links mode has to keep track of things in a table; cleaning it up at the end of the operation is a waste of time. Someone "fixed" the leak to make valgrind happy and by doing so introduced a performance regression. Another example might be a compiler; it's pointless to deal…

Is there is a way to tell Valgrind that a certain memory allocation is intentionally being "leaked", and should not produce a warning?

Re: Does memory leak? (1995)

#149

Post by TedDoesntTalk »

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…

To offer a contrarian point of view: I’d jump at such an opportunity... to work in such a technically interesting area AND help keep my country technologically relevant. It’s a no-brainer.

Re: Does memory leak? (1995)

#150

Post by ibrault »

enriquto wrote: post #121
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…

> 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...

I can testify first-hand that the "functions in a single page" and "avoid the pre-processor" rules are not followed very closely haha
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