From: "slyphon (Jonathan Simms)" <slyphon@...>
Date: 2012-05-16T05:36:40+09:00
Subject: [ruby-core:45065] [Ruby 1.8 - Bug #6438][Open] Ruby Queue in thread before fork causes segfault on GC


Issue #6438 has been reported by slyphon (Jonathan Simms).

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Bug #6438: Ruby Queue in thread before fork causes segfault on GC
https://bugs.ruby-lang.org/issues/6438

Author: slyphon (Jonathan Simms)
Status: Open
Priority: High
Assignee: 
Category: ext
Target version: Ruby 1.8.7
ruby -v: ruby 1.8.7 (2012-02-08 patchlevel 358) [i686-darwin11.3.0]


After many hours of debugging (with immeasurable help from Eric Lindvall), I've come across a pretty nasty bug in MRI 1.8.7 that affects p249-p358 on linux and OSX.

Eric came up with this reproduction:

require 'thread'
50.times { Thread.new { Queue.new.pop } }
Process.waitpid fork { GC.start; puts "In child: #{$$}" }

produces the output: 

/tmp/fork-crash.rb:3: [BUG] Segmentation fault
ruby 1.8.7 (2012-02-08 patchlevel 358) [i686-darwin11.3.0]

More specifically, this seems to be a problem with a Thread waiting on a ConditionVariable when you fork

require 'thread'
50.times { Thread.new { m = Mutex.new; c = ConditionVariable.new; m.synchronize { c.wait(m) } } }
Process.waitpid fork { GC.start; puts "In child: #{$$}" }

produces the output:

/tmp/mutex-crash.rb:3: [BUG] Segmentation fault
ruby 1.8.7 (2012-02-08 patchlevel 358) [i686-darwin11.3.0]




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