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Bug #17203

Logger::Formatter won't work with non main Ractor

Added by maciej.mensfeld (Maciej Mensfeld) 2 months ago. Updated about 1 month ago.

Status:
Closed
Priority:
Normal
Target version:
-
ruby -v:
ruby 3.0.0preview1 (2020-09-25 master 0096d2b895) [x86_64-linux]
[ruby-core:100216]

Description

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:

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/

Updated by Eregon (Benoit Daloze) 2 months ago

  • 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.

Updated by Eregon (Benoit Daloze) 2 months ago

I tried to make an example why sharing a mutable object is problematic, but I think I just got more confused :D

ruby -e '$stdout.instance_variable_set(:@private, Object.new); p $stdout.object_id; p $stdout.instance_variables; Ractor.new { p $stdout.object_id; p $stdout.instance_variables; p $ $stdout.instance_variable_get(:@private) }.take'
60
[:@private]
<internal:ractor>:38: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
80
[]
nil

So $stdout in each Ractor is a different object?
Might be a good way to still let p/print/puts work in Ractors.
The $stdout variable is Ractor-local, so that might make sense.

This sometimes trigger a [BUG]:

$ ruby -e 'p $stdout.object_id; 10.times.map { Ractor.new { p $stdout.object_id } }; sleep 1'
60
<internal:ractor>:38: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
80
100
120
140
160
180220200


240
260
-e: [BUG] Object ID seen, but not in mapping table: 0x000055a75f933080 [0    U] T_ZOMBIE 

ruby 3.0.0dev (2020-09-29T15:32:22Z master c38605de6b) [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0001 p:0000 s:0003 E:000b10 (none) [FINISH]


-- C level backtrace information -------------------------------------------
[0x55a75e3b5c6e]
/home/eregon/prefix/ruby-master/bin/ruby(rb_bug+0xe5) [0x55a75e1be426] error.c:723
/home/eregon/prefix/ruby-master/bin/ruby(obj_free_object_id+0x19) [0x55a75e1e9fe8] gc.c:2691
/home/eregon/prefix/ruby-master/bin/ruby(finalize_list) gc.c:2679
[0x55a75e1ee213]
/home/eregon/prefix/ruby-master/bin/ruby(rb_ec_cleanup+0x2e8) [0x55a75e1cf558] eval.c:173
[0x55a75e1cfcc1]
/home/eregon/prefix/ruby-master/bin/ruby(main+0x6f) [0x55a75e1c32ef] ./main.c:50

Updated by ko1 (Koichi Sasada) 2 months ago

Eregon (Benoit Daloze) wrote in #note-1:

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

I agree. it should be read from any ractors.

Updated by Eregon (Benoit Daloze) about 1 month ago

  • Status changed from Open to Closed

The PR was merged, and $$ can be accessed from Ractors in #17268, I think we can close this.

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