[ruby-core:100221] [Ruby master Bug#17203] Logger::Formatter won't work with non main Ractor

Issue #17203 has been updated by Eregon (Benoit Daloze).

Assignee set to ko1 (Koichi Sasada)

Since `$$` returns a (read-only) Integer, it seems harmless to let Ractors read it.

Although I think `Process.pid` is nicer than `$$` :)

`$stdout` OTOH should not be possible to access from non-main Ractor, no matter the access path.
It's a mutable object, if it's shared between Ractors it can lead to segfaults.

----------------------------------------
Bug #17203: Logger::Formatter won't work with non main Ractor
https://bugs.ruby-lang.org/issues/17203#change-87810

* Author: maciej.mensfeld (Maciej Mensfeld)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: ruby 3.0.0preview1 (2020-09-25 master 0096d2b895) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
``` ruby
class Rogger < Ractor
  def self.new
    super do
      # STDOUT cannot be referenced but $stdout can
      logger = ::Logger.new($stdout)
 
      # Run the requested operations on our logger instance
      while data = recv
        logger.public_send(data[0], *data[1])
      end
    end
  end
  
  # Really cheap logger API :)
  def method_missing(m, *args, &_block)
    self << [m, *args]
  end
end
 
class Rails
  LOGGER = Rogger.new
 
  def self.logger
    LOGGER
  end
end
 
Ractor.new do
  Rails.logger.info "Hello"
end
```

running this ends up with:

```bash
terminated with exception (report_on_exception is true):
ruby/3.0.0/logger/formatter.rb:15:in `call': can not access global variables $$ from non-main Ractors (RuntimeError)
  from ruby/3.0.0/logger.rb:586:in `format_message'
  from ruby/3.0.0/logger.rb:476:in `add'
  from ruby/3.0.0/logger.rb:529:in `info'
  from test.rb:23:in `public_send'
  from test.rb:23:in `block in new'
```

however the same with fixed formatter works.

PR: https://github.com/ruby/ruby/pull/3600


All of the code examples are here: https://mensfeld.pl/2020/09/building-a-ractor-based-logger-that-will-work-with-non-ractor-compatible-code/



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