[ruby-core:97280] [Ruby master Feature#16476] Socket.getaddrinfo cannot be interrupted by Timeout.timeout

Issue #16476 has been updated by mame (Yusuke Endoh).

Backport deleted (2.5: UNKNOWN, 2.6: UNKNOWN)
ruby -v deleted (ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux])
Assignee set to Glass_saga (Masaki Matsushita)
Status changed from Open to Assigned
Tracker changed from Bug to Feature

We discussed this issue at the dev-meeting, and it requires @Glass_saga's review.

Note:

* It is uninterruptable under a platform that getaddrinfo_a is unavailable, but this problem is not only this proposal but also `timeout:` option of `Addrinfo.getaddrinfo()`. 
* Interruptable version can be implemented without getaddrinfo_a: Creating pthread for getaddrinfo function and pthread_cancel when interrupted.  Contribution is welcome.

----------------------------------------
Feature #16476: Socket.getaddrinfo cannot be interrupted by Timeout.timeout
https://bugs.ruby-lang.org/issues/16476#change-84397

* Author: kirs (Kir Shatrov)
* Status: Assigned
* Priority: Normal
* Assignee: Glass_saga (Masaki Matsushita)
----------------------------------------
It seems like the blocking syscall done by `Socket.getaddrinfo` blocks Ruby VM in a way that Timeout.timeout has no effect.
See reproduction steps in getaddrinfo_interrupt.rb (https://gist.github.com/kirs/00c02ef92e0418578135fe0a6cbd3d7d). This affects all modern Ruby versions, including the latest 2.7.0.

Combined with default 10s resolv timeout on many Linux systems, this can have a very noticeable effect on production Ruby apps being not resilient to slow DNS resolutions, and being unable to fail fast even with `Timeout.timeout`.

While https://bugs.ruby-lang.org/issues/15553 improves the situation for `Addrinfo.getaddrinfo`, `Socket.getaddrinfo` is still blocking the VM and Timeout has no effect.

I'd like to discuss what could be done to make that call non-blocking for threads in Ruby VM.

**UPD:** looking closer, I can see that `Socket.getaddrinfo("www.ruby-lang.org", "http")` and `Addrinfo.getaddrinfo("www.ruby-lang.org", "http")` call non-interruptible `getaddrinfo`, while `Addrinfo.getaddrinfo("www.ruby-lang.org", "http", timeout: 10)` calls `getaddrinfo_a`, which is interruptible:

``` ruby
# interrupts as expected
Timeout.timeout(1) do
  Addrinfo.getaddrinfo("www.ruby-lang.org", "http", timeout: 10)
end
```

I'd maybe suggest that we try to *always* use `getaddrinfo_a` when it's available, including in `Socket.getaddrinfo`. What downsides that would have?
I'd be happy to work on a patch.



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