From: Michael Malone <michael.malone@...>
Date: 2009-03-09T12:15:11+09:00
Subject: Re: 1.9.x Thread problem

>
>>> If I run this using either ruby 1.9.1p0 (2009-01-30 revision 21907) 
>>> [i686-linux] or ruby 1.9.2dev (2009-03-05 trunk 22769) [i686-linux] 
>>> I get results I would not expect:
>>> Joining thread , n=
>>>     
>>
>> It hasn't been defined which thread, the created child thread
>> or the creating parent thread, runs first at thread creation.
>> In 1.8, the child runs first by chance.
>>
>>  

I have read and re-read this about 10 times now and this comment makes 
it appear that the contract for Thread.new {block}, where the block is 
run exclusively in the newly created thread, is violated.
> Can you then explain why it runs consistently like this or a way in 
> which I can guarantee I am running in the first created child thread?  
> I would have expected to be inside of the child thread because the 
> code setting up the :index is inside the block passed to 
> Thread.new().  And I only  put the created child Thread instances in 
> the Queue, so I should _only_ get child Thread instances when I call 
> Queue#pop.
 require 'thread'
 THREADS = 10

 parent_id = Thread.current.object_id

 queue = Queue.new
 THREADS.times do |i|
    queue << Thread.new do
       th = Thread.current
       th[:index] = i
       raise "Running inside parent" if th.object_id == parent_id
       sleep(2)
    end
 end

 THREADS.times do
    th = queue.pop
    raise "Running inside parent" if th.object_id == parent_id
    puts "Joining thread #{th[:index]}"
    th.join()
 end

I have simplified and changed things.  I am quite certain that the 
parent thread is not being joined or indeed added to the queue as no 
exceptions are raised (unless this is a bad test) and I still get the 
same (strange) output.  Any other ideas?


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