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Subject: Re: Ruby Tempfile can cause unexpected infinite loop in REE 1.8.7
From: WU Chehai <wuche...@gmail.com>
To: Ruby Enterprise Edition <emm-ruby@googlegroups.com>
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Actually, regular Ruby 1.8.7-p330 does not has this issue.

The regular Ruby 1.8.7 finalizes objects every time a node is evaled
if some conditions are met, so the temp file object (temp) is
finalized before the thread exists. Everything should be fine.

Therefore, this is a bug in current REE 1.8.7

On Jan 17, 4:34=A0pm, WU Chehai <wuche...@gmail.com> wrote:
> Hi, all
>
> The following code ends up an infinite loop
>
> require "tempfile"
> GC.stress =3D true
> t =3D Thread.new do
> =A0 temp =3D Tempfile.new("tmp")
> =A0 temp << "something"
> =A0 temp =3D nil
> =A0 h =3D Hash.new
> end
> t.join
>
> Our analysis shows that there is a race condition in REE 1.8.7:
>
> - When a thread finishes running, REE/Ruby dequeues it
> (rb_thread_remove) =A0from the global thread list and calls
> rb_thread_schedule in order to schedule another thread to run.
>
> - rb_thread_schedule invokes =A0rb_gc_finalize_deferred before
> scheduling another thread.
>
> - rb_gc_finalize calls finalizer on Ruby Tempfile object. The
> finalizer closes a file descriptor by calling rb_thread_fd_close
>
> - rb_thread_fd_close has a loop to iterate over all threads.
>
> - However, the current thread is already dequeued (it points to other
> threads, but no threads point back to it), so the loop is actually an
> infinite loop.
>
> We believe this issue also exists in regular Ruby 1.8.7, but we cannot
> reproduce it. Is this a bug in REE 1.8.7?
>