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Does memory leak? (1995)

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Re: Does memory leak? (1995)

#211

Post by int_19h »

tomcam wrote: post #182
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 mean all due respect with this question. Not an attack. Do you think your country should have such missiles? If not, how would you handle the defense case in which your country is attacked but does not have them? Also note that most of Europe is defended by these missiles made in the USA.

In the real world, the dilemma is more often, "do you think your country, and all other countries it considers allies, should have such missiles"?

Right now, for example, Saudi Arabia is bombing Yemen with American-made bombs, and Turkey is using German tanks and Italian drones to grind Kurdish towns and villages into rubble in Syria.

Re: Does memory leak? (1995)

#212

Post by diego »

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…

If you want a "toy" example of this type of code, look at flight control software for drones such as Betaflight. You can modify this code and test it in real life. I did this, as I contributed the GPS Rescue feature. I have a blooper reel of failures during testing.

https://github.com/betaflight/betaflight/

Re: Does memory leak? (1995)

#213

Post by [deleted] »

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?

[deleted]

Re: Does memory leak? (1995)

#214

Post by asdfasgasdgasdg »

saagarjha wrote: post #112
asdfasgasdgasdg wrote: post #107

Earlier quoted context omitted.

I've never heard that use of the term "arena". Are you thinking of slabs? Arenas are typically allocated and deallocated at once. That's their main feature.

https://sourceware.org/glibc/wiki/MallocInternals#Arenas_and...

Seems like a bit of an ideosyncratic use of the word. In tcmalloc these per thread zones are just called the thread cache (hence the name "thread caching malloc").

Re: Does memory leak? (1995)

#215

Post by Baeocystin »

AlotOfReading wrote: post #193
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…

Having worked on embedded systems for a decade at this point, the fact that we allow vendors to get away with providing ancient compilers and runtimes is shameful. We know that these old toolchains have thousands of documented bugs, many critical. We know how to produce code with better verification, but just don't push for the tools to do it.

Isn't the key part that these older systems have documented bugs?

Or, to put it another way, if there's a wasp in the room (and there always is), I'd want to know where it is.

Re: Does memory leak? (1995)

#216

Post by AlotOfReading »

Baeocystin wrote: post #215
AlotOfReading wrote: post #193

Earlier quoted context omitted.

Having worked on embedded systems for a decade at this point, the fact that we allow vendors to get away with providing ancient compilers and runtimes is shameful. We know that these old toolchains have thousands of documented bugs, many critical. We know how to produce code with better verification, but just don't push for the tools to do it.

Isn't the key part that these older systems have documented bugs? Or, to put it another way, if there's a wasp in the room (and there always is), I'd want to know where it is.

That doesn't end up being the case for a number of reasons. Firstly, no one is actually able to account of all of these known issues a priori. I don't like calling things impossible, but writing safe C that avoids any compiler bugs is probably best labeled as that.

Secondly, vendors make modifications during their release process, which introduces new (and fun!) bugs. You're not really avoiding hidden wasps, just labeling some of them. If you simply moved to a newer compiler, you wouldn't have to avoid them, they'd mostly be gone (or at worst, labeled).

Re: Does memory leak? (1995)

#217

Post by DavidVoid »

TedDoesntTalk wrote: post #146
cushychicken wrote: post #57

Earlier quoted context omitted.

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?

Or maybe they trust/value their peer's judgement despite the fact that they themselves don't have any strong views on the subject?

Re: Does memory leak? (1995)

#218

Post by ficklepickle »

lonelappde wrote: post #173
bathtub365 wrote: post #56

Earlier quoted context omitted.

What’s your rationale for picking an order of magnitude instead of, say, double?

Double is an order of magnitude.

I suppose it is, in binary. Although humans generally use base 10.

I might have to start saying "a binary order of magnitude" instead of "double" when circumstances call for gobbledygook.

Re: Does memory leak? (1995)

#219

Post by Baeocystin »

AlotOfReading wrote: post #216
Baeocystin wrote: post #215

Earlier quoted context omitted.

Isn't the key part that these older systems have documented bugs? Or, to put it another way, if there's a wasp in the room (and there always is), I'd want to know where it is.

That doesn't end up being the case for a number of reasons. Firstly, no one is actually able to account of all of these known issues a priori. I don't like calling things impossible, but writing safe C that avoids any compiler bugs is probably best labeled as that. Secondly, vendors make modifications during their release process, which introduces new (and fun!) bugs. You're not really avoiding hidden wasps, just lab…

Are the newer compilers truly that much better? I've been working in tech since the 90's, and I can't say that for the tools I've used I've noticed any great improvement in overall quality- bugs get swatted, new ones created in what feels like a constant measure. I am assuming that many optimizations are turned off regardless, due to wanting to keep the resulting assembly as predictable as possible, but I do not work in the embedded space, so this is perhaps a naive question.

Re: Does memory leak? (1995)

#220

Post by acqq »

GordonS wrote: post #192
acqq wrote: post #168

Earlier quoted context omitted.

> I wish deleting lots of files would be much, much faster. You've got time to make a cup of coffee if you need to delete a node_modules folder The example I gave was for the old times when people had much less RAM and the disks had to move physical heads to access different areas. Now with the SSDs you shouldn't be able to experience it that bad (at least when using lower level approaches). How do you start that act…

Even with an SSD, it's still bad. Much better than the several minutes it used to take with an HDD, but still annoying. I just tried deleting a node_modules folder with 18,500 files in it, hosted on an NVMe drive. Deleting from Windows Explorer, it took 20s. But then I tried `rmdir /s /q` from your SU link - 4s! I remember trying tricks like this back with an HDD, but don't remember it having such a dramatic impact.

>>> You've got time to make a cup of coffee if you need to delete a node_modules folder...

> Deleting from Windows Explorer, it took 20s.

> `rmdir /s /q` from your SU link - 4s

OK, so you saw that your scenarios could run much better, especially if Windows Explorer is avoided. But in Explorer, is that time you measured with deleting to the Recycle Bin or with the Shift Delete (which deletes irreversibly but can be faster)?

Additionally, I'd guess you don't have to wait at all (i.e. you can reduce it to 0 seconds) if you first rename the folder and than start deleting that renamed one and let it doing that in the background while continuing with your work -- e.g. if you want to create the new content in the original location it's immediately free after the rename, and the rename is practically immediate.

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