sass-embedded `Resource temporarily unavailable` under JRuby with Java 21 about sass-embedded-host-ruby HOT 10 CLOSED

It's the child_io who needs to be patched, rather than the parent_io. The return value of popen3 is parent_io. Therefore, popen3 has to be patched internally.

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I have to take a more detailed look but most likely JDK21 + JRuby issue with stdio handling in the open3 gem.

The code path that Dart VM ran into issue is where it’s trying to write its stdout to send response back to Ruby side. - This means at least the Dart VM received the request properly, so that sprockets, sassc-embedded, sass-embedded, and protobuf are all likely working.

The stdout of a child process can get stuck if the polling thread from the parent process is not working properly. If the stdout pipe buffer is completely full, and the parent process is not consuming the buffer at all, the whole child process can get stuck.

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@chadlwilson Also, was it on windows or unix-like, or both? JRuby has different I/O implementation for open3 on windows and unix-like.

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This was on MacOS Sonoma 14.5 (sorry, updated description) but I can give it a go on Linux if that helps (sounds like probably roughly the same behaviour expected though?).

I haven't yet attempted on Windows; usually that's the "final frontier" :D

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Hmm, could it be jruby/jruby#8235 or jruby/jruby#8069 or jruby/jruby#8234 ?

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I can reproduce this in CI with the following code:

    10000.times do |i|
      Sass.compile_string('a{b:c}' * i).css
      puts i
    end

On windows it works to the end. However on unix-like, this works until the 4368th iteration but fails at the 4369th iteration.

On the 4368th iteration, the size of protobuf reply message is 65530 bytes, and on the 4369th iteration the size of reply message is 65545 bytes.

require 'sass-embedded'

Sass.compile_string('a{b:c}' * 4368).css # works, stdout reply size is 65530 bytes
Sass.compile_string('a{b:c}' * 4369).css # fails, stdout reply size is 65545 bytes.

It must be jruby/jruby#8235.

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OK, will close this for now and track there. Thanks for the effort, as always!

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I tried to monkey patch the Connection class and streams as in jruby/jruby#8235 (comment) but my Ruby and monkey-patching abilities are probably a bit too limited for that one :)

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# frozen_string_literal: true

require 'fcntl'

module Open3
  _popen_run = instance_method(:popen_run)
  define_method(:popen_run) do |cmd, opts, child_io, parent_io, &block|
    child_io.each do |io|
      flags = io.fcntl(Fcntl::F_GETFL)
      io.fcntl(Fcntl::F_SETFL, flags | (Fcntl::O_NONBLOCK))
      io.fcntl(Fcntl::F_SETFL, flags & (~Fcntl::O_NONBLOCK))
    end
    _popen_run.bind(self).call(cmd, opts, child_io, parent_io, &block)
  end
  module_function :popen_run
  class << self
    private :popen_run
  end
end

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Works like a dream! Didn't think of trying to monkey patch popen directly.

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