[ruby-core:114528] [Ruby master Feature#17678] Ractors do not restart after fork

25 Aug 2023

      Issue #17678 has been updated by ivoanjo (Ivo Anjo).
...
The addition of Ractor#alive? and/or Ractor#status makes sense to me. Even in non-forked processes such methods could be useful. Note that you can get what you want already, by calling Ractor#inspect, so these methods would only need to expose information that Ractor is already storing.
Thanks for looking into this!

I don't think the info is there in #inspect... At least I don't get it on stable or latest ruby-head? 😅

Here's an updated example:

```ruby
puts RUBY_DESCRIPTION

r2 = Ractor.new { puts "[#{Process.pid}] Ractor started!"; sleep(1000) }

puts "[#{Process.pid}] In parent process, ractor status is #{r2.inspect}"

sleep(1)
puts "[#{Process.pid}] Forking..."

fork do
  puts "[#{Process.pid}] In child process, ractor status is #{r2.inspect}"
end

Process.wait
```

and here's what I get:

```
$ ruby ractor-test.rb
ruby 3.3.0dev (2023-08-24T12:12:51Z master 5ec1fc52c1) [x86_64-linux]
ractor-test.rb:3: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
[10] In parent process, ractor status is #<Ractor:#2 ractor-test.rb:3 blocking>
[10] Ractor started!
[10] Forking...
[12] In child process, ractor status is #<Ractor:#2 ractor-test.rb:3 blocking>
```

----------------------------------------
Feature #17678: Ractors do not restart after fork
https://bugs.ruby-lang.org/issues/17678#change-104327

* Author: ivoanjo (Ivo Anjo)
* Status: Assigned
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
----------------------------------------
Hello there! I'm working at Datadog on the `ddtrace` gem -- <https://github.com/DataDog/dd-trace-rb> and we're experimenting with using Ractors in our library but run into a few issues.

### Background

When running a Ractor as a background process, the Ractor stops & does not restart when the application forks.

### How to reproduce (Ruby version & script)

`ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-linux]`

```ruby
r2 = Ractor.new do
 loop { puts "[#{Process.pid}] Ractor"; sleep(1) }
end

sleep(1)
puts "[#{Process.pid}] Forking..."

fork do
 sleep(5)
 puts "[#{Process.pid}] End fork."
end

loop do
 sleep(1)
end
```

### Expectation and result

The application prints “Ractor” each second in the main process, but not in the fork.

Expected the Ractor (defined as `r2`) to run in the fork.

```
[29] Ractor
[29] Ractor
[29] Forking...
[29] Ractor
[29] Ractor
[29] Ractor
[29] Ractor
[29] Ractor
[32] End fork.
[29] Ractor
[29] Ractor
[29] Ractor
```

### Additional notes

Threads do not restart across forks either, so it might not be unreasonable to expect consistent behavior. However, it’s possible to detect a dead Thread and recreate it after a fork (e.g. with `#alive?`, `#status`), but there’s no such mechanism for Ractors.

### Suggested solutions

1. Auto-restart Ractors after fork
2. Add additional methods to Ractors that allow users to check & manage the status of the Ractor, similar to Thread.

-- 
https://bugs.ruby-lang.org/