From: "mame (Yusuke Endoh) via ruby-core" <ruby-core@...>
Date: 2023-11-02T08:07:37+00:00
Subject: [ruby-core:115225] [Ruby master Feature#16476] Socket.getaddrinfo cannot be interrupted by Timeout.timeout

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

Status changed from Open to Closed

#19965 solved the problem, so I'll close it.

I completely forgot this ticket, but the concept (pthread_create on every call to getaddrinfo(3)) was the same as in #19965. Just for case, #19965 is a bit more elaborate:

* It works as before in environments where pthread is not available.
* It includes the same hack for not only `getaddrinfo(3)` but also `getnameinfo(3)`.
* `pthread_cancel` is not used because until recently [there was a bug in glibc](https://bugzilla.redhat.com/show_bug.cgi?id=1405071) where `pthread_cancel` of a pthread that is calling `getaddrinfo(3)` would cause subsequent name resolution to stick: 
* It attempts to use `pthread_setaffinity_np` to reduce speed degradation.

----------------------------------------
Feature #16476: Socket.getaddrinfo cannot be interrupted by Timeout.timeout
https://bugs.ruby-lang.org/issues/16476#change-105143

* Author: kirs (Kir Shatrov)
* Status: Closed
* 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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