serve() fails when run from an :interactive thread (Julia >=1.9)

[robsmith11]

The minimal example fails to return a valid response (but doesn't throw any errors) when run from an :interactive thread, but works fine if :interactive is removed. Julia should be started with -t2,1.

import HTTP

function run()
  HTTP.serve() do request::HTTP.Request
    return HTTP.Response(200, "hello")
  end
end

t = Threads.@spawn :interactive run()
wait(t)

$ curl -v 127.0.0.1:8081
*   Trying 127.0.0.1:8081...
* Connected to 127.0.0.1 (127.0.0.1) port 8081 (#0)
> GET / HTTP/1.1
> Host: 127.0.0.1:8081
> User-Agent: curl/7.85.0
> Accept: */*
>
* Empty reply from server
* Closing connection 0
curl: (52) Empty reply from server

(foo) pkg> st
Status `/tmp/foo/Project.toml`
  [cd3eb016] HTTP v1.5.5

julia> versioninfo()
Julia Version 1.10.0-DEV.46
Commit d0a211a9209 (2022-11-24 15:42 UTC)
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 8 × AMD Ryzen 7 4700U with Radeon Graphics
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-14.0.6 (ORCJIT, znver2)
  Threads: 3 on 8 virtual cores
Environment:
  JULIA_DEPOT_PATH = /me/.julia

I also tested and got the same results with 1.9.0-alpha1.

[fonsp]

(This issue is about the new :interactive thread feature in Julia. See the PR and new docs.)

[quinnj]

Thanks for the report; this is somewhat due to my own naivety with how the new threadpools work in Julia, so it was a good learning experience for me. It's actually not really related to the server code really, but due to our utilities we have around global objects that we try to make threadsafe via resize!ing them during __init__ and then using the current Threads.threadid() to access the appropriate element. The problem is we're sizing those arrays with only Threads.nthreads(), which isn't accurate in the the threadpool world. Luckily, there's a new Threads.maxthreadid() function that is more appropriate for how we're using these global arrays. Fix is up: #972