Async DNS
51 points
2 hours ago
| 6 comments
| flak.tedunangst.com
| HN
btown
52 seconds ago
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For those using it in Python, Gevent provides a pluggable set of DNS resolvers that monkey-patch the standard library's functions for async/cooperative use, including one built on c-ares: https://www.gevent.org/dns.html
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albertzeyer
1 hour ago
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The first linked article was recently discussed here: RIP pthread_cancel (https://news.ycombinator.com/item?id=45233713)

In that discussion, most of the same points as in this article were already discussed, specifically some async DNS alternatives.

See also here the discussion: https://github.com/crystal-lang/crystal/issues/13619

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frumplestlatz
52 minutes ago
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I am always amused when folks rediscover the bad idea that is `pthread_cancel()` — it’s amazing that it was ever part of the standard.

We knew it was a bad idea at the time it was standardized in the 1990s, but politics — and the inevitable allure of a very convenient sounding (but very bad) idea — meant that the bad idea won.

Funny enough, while Java has deprecated their version of thread cancellation for the same reasons, Haskell still has theirs. When you’re writing code in IO, you have to be prepared for async cancellation anywhere, at any time.

This leads to common bugs in the standard library that you really wouldn’t expect from a language like Haskell; e.g. https://github.com/haskell/process/issues/183 (withCreateProcess async exception safety)

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AndyKelley
5 minutes ago
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What's crazy is that it's almost good. All they had to do was make the next syscall return ECANCELED (already a defined error code!) rather than terminating the thread.

Musl has an undocumented extension that does exactly this: PTHREAD_CANCEL_MASKED passed to pthread_setcancelstate.

It's great and it should be standardized.

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brcmthrowaway
8 minutes ago
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Who can fix getaddrinfo?
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javantanna
1 hour ago
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Just curious how you approached performance bottlenecks — anything surprising you discovered while testing?
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01HNNWZ0MV43FF
1 hour ago
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It's weird to me that event-based DNS using epoll or similar doesn't have a battle-tested implementation. I know it's harder to do in C than in Rust but I'm pretty sure that's what Hickory does internally.
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frumplestlatz
48 minutes ago
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it’s a weird problem, in that (1) DNS is hard, and (2) you really need the upstream vendor to solve the problem, because correct applications want to use the system resolver.

If you don’t use the system resolver, you have to glue into the system’s configuration mechanism for resolvers somehow … which isn’t simple — for example, there’s a lot of complex logic on macOS around handling which resolver to use based on what connections, VPNs, etc, are present.

And the there’s nsswitch and other plugin systems that are meant to allow globally configured hooks plug into the name resolution path.

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benatkin
1 hour ago
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