[ruby-core:117321] [Ruby master Bug#20393] `after_fork_ruby` clears all pending interrupts for both parent and child process.

["ioquatix (Samuel Williams) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20393 has been reported by ioquatix (Samuel Williams).

----------------------------------------
Bug #20393: `after_fork_ruby` clears all pending interrupts for both parent and child process.
https://bugs.ruby-lang.org/issues/20393

* Author: ioquatix (Samuel Williams)
* Status: Open
* Assignee: ioquatix (Samuel Williams)
* Backport: 3.0: REQUIRED, 3.1: REQUIRED, 3.2: REQUIRED, 3.3: REQUIRED
----------------------------------------
In the following program, the behaviour of the parent process is affected by whether `Process.fork` is invoked or not.

```ruby
Thread.handle_interrupt(RuntimeError => :never) do
  Thread.current.raise(RuntimeError, "Queued error")
  
  puts "Pending interrupt: #{Thread.pending_interrupt?}" # true
  
  pid = Process.fork do
    puts "Pending interrupt (child process): #{Thread.pending_interrupt?}"
    Thread.handle_interrupt(RuntimeError => :immediate){}
  end
  
  _, status = Process.waitpid2(pid)
  puts "Child process status: #{status.inspect}"
  
  puts "Pending interrupt: #{Thread.pending_interrupt?}" # false
end

puts "Exiting..."
```

I don't think the parent process pending interrupts should be cleared by `after_fork_ruby`:

```c
static void
after_fork_ruby(rb_pid_t pid)
{
    rb_threadptr_pending_interrupt_clear(GET_THREAD());
    if (pid == 0) {
        // child
        clear_pid_cache();
        rb_thread_atfork();
    }
    else {
        // parent
        after_exec();
    }
}
```

How about this implementation:

```c
static void
after_fork_ruby(rb_pid_t pid)
{
    if (pid == 0) {
        // child
        rb_threadptr_pending_interrupt_clear(GET_THREAD());
        clear_pid_cache();
        rb_thread_atfork();
    }
    else {
        // parent
        after_exec();
    }
}
```

cc @ko1



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