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Debugging in the Multiverse

antithesis.com

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Re: Debugging in the Multiverse

#31

Post by casept »

dzaima wrote: post #25
spencerflem wrote: post #20

Earlier quoted context omitted.

There's languages that support time travel debugging, like RR for GDB, or smalltalk, but no open source system wide thing like Antithesis that I know of yet.

rr can record process trees; i.e. basically any part/descendant of a process you spawn will be recorded and can be replayed (userspace CPU & memory, that is); won't record the entire OS though.

My experience with RR is that the chance of it working without hitting a missing syscall or desync is only about 50%, which is why I want a different solution that doesn't rely on the fragile syscall recording approach.

Re: Debugging in the Multiverse

#32

Post by dzaima »

casept wrote: post #31
dzaima wrote: post #25

Earlier quoted context omitted.

rr can record process trees; i.e. basically any part/descendant of a process you spawn will be recorded and can be replayed (userspace CPU & memory, that is); won't record the entire OS though.

My experience with RR is that the chance of it working without hitting a missing syscall or desync is only about 50%, which is why I want a different solution that doesn't rely on the fragile syscall recording approach.

Huh. In my experience it works nearly flawlessly, certainly far above 50%. And even when there are spurious failures in replaying it's easy enough to just re-replay (though I do wish there was some way to export the current position & checkpoints with instruction-level precision to import in a fresh replay). I suppose it depends massively on the recorded program (most of mine are simple C programs, but also a decent bit of Java for JIT inspection or FFI, and I've also recorded an Electron app a couple times, and for fun Factorio)

Re: Debugging in the Multiverse

#33

Post by the_sleaze_ »

barumrho wrote: post #15
mattgreenrocks wrote: post #14

It is really interesting to me that this sort of thing didn’t come from programming language folks like I’d expect. You’d think PLs are in the absolute perfect spot to implement things, because they define the semantics and runtime. And there are a few PLs who have time-travel demos, but they’ve never really been seen as more than a cool tech demo. Perhaps the language is too small a vantage point to really get into…

Elm debugger did something like this, but it's much more limited in scope.

As does Vue - in 5+ years I've never used it

Re: Debugging in the Multiverse

#34

Post by munificent »

mattgreenrocks wrote: post #14

It is really interesting to me that this sort of thing didn’t come from programming language folks like I’d expect. You’d think PLs are in the absolute perfect spot to implement things, because they define the semantics and runtime. And there are a few PLs who have time-travel demos, but they’ve never really been seen as more than a cool tech demo. Perhaps the language is too small a vantage point to really get into…

I know time-travel debugging is very very close to Gilad Bracha's heart and something he was really hoping would make its way into Dart.

I don't know to what degree this is true for other language teams but one thing I've observed is that language designers, compiler people, VM people, and IDE/debugger people have more distinct cultures than you might expect. That can make it hard to ship features that cut across those domains. I think we've gotten a lot better at doing that kind of holistic design on the Dart team, but it took years of team-building to get there.

Re: Debugging in the Multiverse

#36

Post by Veserv »

gguergabo wrote: post #2

Antithesis employee here. Happy to jump in and answer any burning questions people might have about multiverse debugging.

Is the hypervisor multicore? How do you handle shared memory non-determinism? What is the runtime slowdown for shared memory multicore (lets say 16 cores if you need a concrete example) execution?

Re: Debugging in the Multiverse

#40

Post by GuB-42 »

mattgreenrocks wrote: post #14

It is really interesting to me that this sort of thing didn’t come from programming language folks like I’d expect. You’d think PLs are in the absolute perfect spot to implement things, because they define the semantics and runtime. And there are a few PLs who have time-travel demos, but they’ve never really been seen as more than a cool tech demo. Perhaps the language is too small a vantage point to really get into…

From the little I have seen, most programming language folks don't seem to care much about debugging. They care a lot about bugs not happening in the first place, which is good, testability is sometimes taken in consideration, but not much about what to do after a bug happened.

No language will prevent you from misimplementing the specs, but languages can be designed in such a way that it easy to trace back why the button is green and not red.

It seems like those who are the most serious about debugging are from the video game industry. They get all the cool stuff with time travel, hot reload, etc... So much that I expected to see something about video games, and was surprised it wasn't.

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