From: Joel VanderWerf <vjoel@...>
Date: 2003-08-26T14:17:03+09:00
Subject: Re: fxRuby and errors

Fredrik Jagenheim wrote:
> On Mon, Aug 25, 2003 at 05:28:00AM +0900, Joel VanderWerf wrote:
> 
>>See if this helps:
>>
>>Thread.abort_on_exception = true
>>
>>(assign this at the start of your code). Otherwise, threads other than 
>>the main thread die silently.
> 
> 
> Yes, that worked perfectly. Thanks.
> 
> But it brought me no closer to understanding what really happened to
> the thread that threw the exception.
> 
> Setting abort_on_exception to true indicates that it doesn't /abort/
> when you get an exception by default, and you say it 'dies silently'.
> 
> So, correct me if I'm wrong, the thread dies, and lies dormant until
> reaped by Tread.join? Actually, when I typed that I think I understand
> what really happened. When the thread died due to the exception, it
> was suspended. When join was called, the thread was 'promoted' to the
> main thread with an uncatched exception. And since the main thread
> always abort on uncatched exceptions, we get a 'verbose' abort.

I'm not really sure either, but your explanation makes sense, and here's 
what irb says:

irb(main):001:0> t = Thread.new { raise}
=> #<Thread:0x401f3e60 dead>
irb(main):002:0> Thread.list
=> [#<Thread:0x401d0d08 run>]
irb(main):003:0> t.join
RuntimeError:
         from (irb):1
         from (irb):3:in `join'
         from (irb):3
irb(main):004:0> begin; t.join; rescue Exception; puts "CAUGHT!"; end
CAUGHT!
=> nil

So apparently the thread is 'dead', which is probably not the same thing 
as suspended. But a dead thread can still be joined and you can catch 
its exception (more than once, it seems). Hm, that's good to know.