From: Yura Sokolov <funny.falcon@...>
Date: 2011-12-15T21:19:39+09:00
Subject: [ruby-core:41678] [ruby-trunk - Bug #5754] Double require bug in 1.9.3


Issue #5754 has been updated by Yura Sokolov.


> it doesn't see an entry in the loading table even though t2 is currently loading the file

Has it something common with #5727 ?
----------------------------------------
Bug #5754: Double require bug in 1.9.3
http://redmine.ruby-lang.org/issues/5754

Author: Evan Phoenix
Status: Assigned
Priority: Normal
Assignee: Nobuyoshi Nakada
Category: 
Target version: 
ruby -v: -


There appears a bug in the handling of concurrent requires of the same file. If a thread (t2) is waiting for another thread (t1) to finish requiring the file, but requiring the file raises an exception, t1 signals t2 and t2 tries to require the file itself. But due to how the loading table is managed, if t1 attempts to require the file again right away (or if another thread were to), it doesn't see an entry in the loading table even though t2 is currently loading the file. This causes t1 to begin requiring the file again or sometimes it raises a ThreadError instead. Here is the code I write for rubyspec to show the bug:

        start = false
        fin = false

        $scratch = []
        $con1_ready = false
        $con1_raise = true
        path = "path/to/content/below.rb"

        t1_res = nil
        t2_res = nil

        t1 = Thread.new do
          lambda {
            require(path)
          }.should raise_error(RuntimeError)

          # This hits the bug. Because MRI removes it's internal lock from a table
          # when the exception is raised, this #require doesn't see that t2 is
          # in the middle of requiring the file, so this #require runs when it should
          # not.
          #
          # Sometimes this raises a ThreadError also, but I'm not sure why.
          t1_res = require(path)

          Thread.pass until fin
          $scratch << :t1_post
        end

        t2 = Thread.new do
          Thread.pass until $con1_ready
          begin
            t2_res = require(path)
            $scratch << :t2_post
          ensure
            fin = true
          end
        end

        t1.join
        t2.join

        raise "bug" unless t1_res == false
        raise "bug" unless t2_res == true

        $scratch == [:con_pre, :con_pre, :con_post, :t2_post, :t1_post]

Here is the file being required:

$scratch << :con_pre
$con1_ready = true
sleep 0.5
if $con1_raise
  $con1_raise = false
  raise "con1"
end
sleep 0.5
$scratch << :con_post





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