[ruby-core:102776] [Ruby master Bug#17678] Ractors do not restart after fork

[ruby-core:102776] [Ruby master Bug#17678] Ractors do not restart after fork

[knuckles]

Issue #17678 has been reported by ivoanjo (Ivo Anjo).

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

* Author: ivoanjo (Ivo Anjo)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
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/

[ruby-core:102784] [Ruby master Bug#17678] Ractors do not restart after fork

[hsbt]

Issue #17678 has been updated by hsbt (Hiroshi SHIBATA).

Assignee set to ko1 (Koichi Sasada)
Status changed from Open to Assigned

----------------------------------------
Bug #17678: Ractors do not restart after fork
https://bugs.ruby-lang.org/issues/17678#change-90801

* Author: ivoanjo (Ivo Anjo)
* Status: Assigned
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
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/

[ruby-core:114513] [Ruby master Feature#17678] Ractors do not restart after fork

[jeremyevans0 (Jeremy Evans) via ruby-core]

Issue #17678 has been updated by jeremyevans0 (Jeremy Evans).

Tracker changed from Bug to Feature
ruby -v deleted (ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-linux])
Backport deleted (2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN)

As Ractors always use separate OS threads, and fork only runs the current thread in the forked process, I don't see a way for Ractors to continue where they left off after fork.  I think auto-starting would likely be a bad idea, because auto-starting would not return them to the state they were at fork.

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.

----------------------------------------
Feature #17678: Ractors do not restart after fork
https://bugs.ruby-lang.org/issues/17678#change-104304

* 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.



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

[ivoanjo (Ivo Anjo) via ruby-core]

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.



-- 
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[ruby-core:114538] [Ruby master Bug#17678] Ractors do not restart after fork

[jeremyevans0 (Jeremy Evans) via ruby-core]

Issue #17678 has been updated by jeremyevans0 (Jeremy Evans).

Tracker changed from Feature to Bug
Backport set to 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN

Thanks for that information.  It looks like ractors contain information about their state (shown in `inspect`), but that state is not updated on fork, unlike threads.  So I think there is a bug, and it's that non-main ractors do not have their state to `terminated` upon fork (forking from non-main ractors is going to be prohibited, see #17516).

----------------------------------------
Bug #17678: Ractors do not restart after fork
https://bugs.ruby-lang.org/issues/17678#change-104340

* Author: ivoanjo (Ivo Anjo)
* Status: Assigned
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
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.



-- 
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[ruby-core:114540] [Ruby master Bug#17678] Ractors do not restart after fork

[ivoanjo (Ivo Anjo) via ruby-core]

Issue #17678 has been updated by ivoanjo (Ivo Anjo).


Ack, that seems a reasonable way of looking at this, having a way to detect that the ractor is dead would be enough to write some auto-restart code after fork (Erlang supervisor trees here we go :D).

----------------------------------------
Bug #17678: Ractors do not restart after fork
https://bugs.ruby-lang.org/issues/17678#change-104341

* Author: ivoanjo (Ivo Anjo)
* Status: Assigned
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
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.



-- 
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[ruby-core:114543] [Ruby master Bug#17678] Ractors do not restart after fork

[jeremyevans0 (Jeremy Evans) via ruby-core]

Issue #17678 has been updated by jeremyevans0 (Jeremy Evans).


I updated https://github.com/ruby/ruby/pull/8283 to mark non-main ractors as terminated after fork.

----------------------------------------
Bug #17678: Ractors do not restart after fork
https://bugs.ruby-lang.org/issues/17678#change-104345

* Author: ivoanjo (Ivo Anjo)
* Status: Assigned
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
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.



-- 
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[ruby-core:121919] [Ruby Bug#17678] Ractors do not restart after fork

[jhawthorn (John Hawthorn) via ruby-core]

Issue #17678 has been updated by jhawthorn (John Hawthorn).

Status changed from Assigned to Closed

Sorry @jeremyevans0 I think Aaron and I missed that PR, but we did the same thing in https://github.com/ruby/ruby/pull/12982 which should fix this.

One thing we didn't do that's in your PR is forbid forking from within a Ractor, but that does seem like a prudent restriction (though it could be limiting for those wanting to fork, make some adjustments, exec)

----------------------------------------
Bug #17678: Ractors do not restart after fork
https://bugs.ruby-lang.org/issues/17678#change-113027

* Author: ivoanjo (Ivo Anjo)
* Status: Closed
* Assignee: ractor
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
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/
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