From: Sonny Chee <sonny.chee@...>
Date: 2007-03-30T14:06:52+09:00
Subject: Exceptions occassionally lost by child threads

Hey Guys,

As I understand it, the correct way to pass exceptions between threads
is to explicitly raise them in the target thread... so something like
this works:

a = Thread.new(Thread.current) { |parent|
  ....
    parent.raise err

}

What I'm curious about is that the following code also seems to work:

a = Thread.new {
  begin
    puts 'blue'
    sleep 2;
    raise ArgumentError.new('green')
  rescue Exception => err
    puts "Caught: #{err.message}"
    raise err
  end
}

begin
  while a
    sleep 1
    a = a.join(1)
  end
  puts 'yellow'
rescue Exception => err
  puts "Caught it again: #{err.message}"
end

#blue
#Caught: green
#Caught it again: green

However, if i move the sleep 1 statement to after a = a.join(1), the
exception seems to get lost and the output is:

#blue
#Caught: green
#yellow


Should exceptions automatically propagate from children up to the
parent?  And if so, why should the positioning of something as innocuous
as sleep 1 matter?

Sonny.

-- 
Posted via http://www.ruby-forum.com/.