DeVault: Announcing the Hare programming language [LWN.net]

DeVault: Announcing the Hare programming language

Posted May 2, 2022 13:14 UTC (Mon) by HelloWorld (guest, #56129)
In reply to: DeVault: Announcing the Hare programming language by ddevault
Parent article: DeVault: Announcing the Hare programming language

So what trade-off is that? What does it buy you not to prevent resource leaks and use-after-free bugs statically? Really the only answer I can think of is that it makes the language easier to learn. So you save perhaps a couple of weeks of fighting with the borrow checker in order to later spend months debugging leaks and use-after-free issues – assuming you even find them before they cause a production outage and cost you millions of dollars. That doesn't seem like a good trade-off to me.

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DeVault: Announcing the Hare programming language

Posted May 2, 2022 13:20 UTC (Mon) by ddevault (subscriber, #99589) [Link] (9 responses)

The trade-offs come in the form of the complexity of the language and its implementation, which in Rust's case is utterly out of control. I'm not convinced that borrow checking cannot be done more simply - we intend to research this for Hare - but it's not the holy grail of programming which creates a moral lower class among other language, as the Rust adherents in this thread seem to believe.

DeVault: Announcing the Hare programming language

Posted May 2, 2022 18:17 UTC (Mon) by linuxrocks123 (subscriber, #34648) [Link] (5 responses)

How about this: keep track of all the pointers in the runtime, and, when a memory region is freed, replace all the pointers that refer to it with NULL. Then, if anyone tries to do a use after free, they'll get an immediate crash. This wouldn't be a feature you'd want to have turned on for production code, but it could help a lot during development and testing, and it would avoid burdening the programmer with additional borrow-checking rules. I hope, also, that you'll allow bounds checking and similar features to be turned off after debugging and testing are done: I'd rather not pay the cost of those debugging aids in production.

The reception you've gotten from others in this comment section is very unfortunate, although, given the people involved, I'm also not terribly surprised they're acting this way. A good philosophy for handling negativity from ignorant, opinionated blowhards is to just ignore them and keep doing what you love. I'm sure you'll make something great with Hare.

DeVault: Announcing the Hare programming language

Posted May 2, 2022 18:19 UTC (Mon) by ddevault (subscriber, #99589) [Link] (4 responses)

>How about this: keep track of all the pointers in the runtime

This is a non-starter, it's too expensive. Interesting idea, though. We are planning on writing an optional debug allocator which will address many memory-related bugs, such as use-after-free, in a similar manner to valgrind.

> The reception you've gotten from others in this comment section is very unfortunate, although, given the people involved, I'm also not terribly surprised they're acting this way. A good philosophy for handling negativity from ignorant, opinionated blowhards is to just ignore them and keep doing what you love. I'm sure you'll make something great with Hare.

Thanks :)

DeVault: Announcing the Hare programming language

Posted May 2, 2022 18:53 UTC (Mon) by linuxrocks123 (subscriber, #34648) [Link] (3 responses)

> This is a non-starter, it's too expensive.

What if you used a pool allocator to separate the pointers from the non-pointers? That would add a level of indirection to structs that had pointers, since they'd have to be converted to pointers to pointers, and also to pointers on the stack, since ditto. But then you'd have a nice contiguous array of all your pointers that you'd just have to scan upon calls to free, and you might be able to use SIMD for that.

If you've thought of that and it's too expensive, I'll stop now, but I just thought I'd mention it in case you hadn't thought of it :)

DeVault: Announcing the Hare programming language

Posted May 2, 2022 18:55 UTC (Mon) by ddevault (subscriber, #99589) [Link]

I don't have time to give this idea the thought it deserves right now, but thanks for sharing. Added it to my notes for improvements to allocator insights.

Use-after-free checking at low runtime cost

Posted May 4, 2022 1:12 UTC (Wed) by akkartik (guest, #158307) [Link] (1 responses)

Since you seem interested in this space, I'll throw out one idea I particularly like and have used in a project [1]: manage heap allocations using a fat pointer that includes an allocation id. The pointer contains the allocation id and so does the payload. Every dereference of the fat pointer compares the allocation id in the pointer and payload. Freeing an allocation resets its allocation id. Future allocations that reuse the allocation will never generate the same allocation id. A use-after-free dereference then leads to an immediate abort, which is easier to debug and more secure.

The overhead of this scheme is too great for most C/Rust programmers, but I think it's much lower than tracking all pointers or indirections in structs containing pointers.

[1] https://github.com/akkartik/mu

Use-after-free checking at low runtime cost

Posted May 4, 2022 13:22 UTC (Wed) by HelloWorld (guest, #56129) [Link]

The best that a run-time check for this sort of thing can do is turn one bug into a different kind of bug, at a considerable performance cost. While that can be useful for legacy programming languages like C (primarily as a debugging tool), it's simply the wrong approach for new languages. Modern programming language design should be focused on statically preventing bugs, and messing around with run-time checks is simply a waste of time.

DeVault: Announcing the Hare programming language

Posted May 2, 2022 19:54 UTC (Mon) by HelloWorld (guest, #56129) [Link] (1 responses)

> I'm not convinced that borrow checking cannot be done more simply - we intend to research this for Hare
I don't think something this fundamental can be retrofitted. It specifically says on the Hare website that you intend to place a strong emphasis on backward compatibility, which means that once programs with lifetime issues (leaks/use-after-free) are out there, the compiler needs to be able to compile them, and thus the same bugs can occur in new code as well.

I wish you well with your efforts regarding a simpler borrow checker.

DeVault: Announcing the Hare programming language

Posted May 2, 2022 19:57 UTC (Mon) by ddevault (subscriber, #99589) [Link]

To be clear, we're only committed to backwards compatibility following 1.0. Borrow checker research will be done prior to 1.0.

DeVault: Announcing the Hare programming language

Posted May 2, 2022 23:57 UTC (Mon) by roc (subscriber, #30627) [Link]

Optimizing for a simpler language and implementation makes sense when your audience is mostly the people working on the language and implementation. It makes less sense when your audience is mainly people developing in the language, and even less sense when you also consider users of software developed in the language.

Language simplicity is good for developers, of course, but absence of memory corruption and data races provides another kind of simplicity. (And I think Rust is relatively free of the kind of "accidental" complexity that C and C++ are full of.)