From: "ara.t.howard" <ara.t.howard@...>
Date: 2008-07-16T01:18:45+09:00
Subject: Re: Handling exceptions in Threads


On Jul 15, 2008, at 6:35 AM, Guillermo.Acilu@koiaka.com wrote:

>
> If I leave the Thread.abort_on_exception = false, the algorithm ends  
> after
> triggering about 10 threads. If I set it to  
> Thread.abort_on_exception =
> true, the algorithm end abnormally, but without printing any error
> message.
>
> I have added the following code at the end of the method called by the
> thread:
>
> rescue Exception => error
>    puts "#{error.class}: #{error.message}"
>
> But I cannot get any error message in the console. I am sure that the
> problem is something related with the database, but I do not know  
> how to
> solve the problem if I do not see the error message.
>
> Any ideas?


1) STDERR.puts message

stdout bufferes and can get lost


2) it's *highly* unlikely the db handle is thread safe and, if it is,  
it'll be native thread safe not green thread safe.  aka - you will not  
get anything from using MT to execute your queries.


so, just use producer/consumer to both simplify and speed up your  
application.  for example


q = Queue.new

queries = list_of_queries

done = Object.new.freeze

producer = Thread.new do
   Thread.current.abort_on_exception

   queries.each do |query|
     q.push db.execute(query)
   end

   q.push done
end

while( ( result = q.pop) != done )
   handle_result result
end


you could handle the results in threads too using the same pattern.   
the key is here is simply to eliminate the MT aspect of the db handle  
usage - for sanity and correctness.

cheers.

a @ http://codeforpeople.com/
--
we can deny everything, except that we have the possibility of being  
better. simply reflect on that.
h.h. the 14th dalai lama