From: "luke-gru (Luke Gruber) via ruby-core" <ruby-core@...>
Date: 2023-02-01T22:21:36+00:00
Subject: [ruby-core:112175] [Ruby master Bug#19395] Process forking within non-main Ractor hits rb_bug()

Issue #19395 has been updated by luke-gru (Luke Gruber).


This fixes it:

https://github.com/luke-gru/ruby/commit/0cb53d4458eb09d8a3f70caaa44c688b48bacaaf

The issue is that when there's multiple ractors and you call fork, the other ractor(s) that are in the child process that aren't the new main ractor need to be GC'd, and their mutexes could be in a weird state, so either skip destruction of them or reinitialize them in the child process. Re-init works on my machine but I don't know if it works across platforms.

----------------------------------------
Bug #19395: Process forking within non-main Ractor hits rb_bug()
https://bugs.ruby-lang.org/issues/19395#change-101612

* Author: luke-gru (Luke Gruber)
* Status: Feedback
* Priority: Normal
* ruby -v: 3.2.0
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
```ruby
def test_fork_in_ractor
  r2 = Ractor.new do
    pid = fork do
      exit Ractor.count
    end
    pid
  end
  pid = r2.take
  puts "Process #{Process.pid} waiting for #{pid}"
  _pid, status = Process.waitpid2(pid) # stuck forever
  if status.exitstatus != 1
    raise "status is #{status.exitstatus}"
  end
end
test_fork_in_ractor()
 ```

$ top # shows CPU usage is high for child process



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