[Ironruby-core] [ruby-core:21290] Re: MRI 1.8.6 bug - exit is ignored if ensure clause throws exception which is caught by outer rescue

Shri Borde Shri.Borde at microsoft.com
Mon Jan 12 18:02:17 EST 2009


I was assuming that exit and Thread.current.kill do the same thing, but Tomas pointed out that they are different. Would you expect that "after foo" would get printed even if you replace exit with Thread.current.kill?

Thanks,
Shri

From: ironruby-core-bounces at rubyforge.org [mailto:ironruby-core-bounces at rubyforge.org] On Behalf Of Shri Borde
Sent: Monday, January 12, 2009 2:10 PM
To: ruby-core at ruby-lang.org; ironruby-core at rubyforge.org
Subject: Re: [Ironruby-core] [ruby-core:21290] Re: MRI 1.8.6 bug - exit is ignored if ensure clause throws exception which is caught by outer rescue

OK, I have added a RSpec test, and  have already tagged it as an IronRuby bug.

For reference, .NET allows the equivalent ThreadAbortException to be caught, but automatically rethrows it at the end of the catch/rescue block. The programmer is required to take a separate action (calling Thread.ResetAbort<http://msdn.microsoft.com/en-us/library/system.threading.thread.resetabort.aspx>) to complete cancel the abort operation. This prevents situations where one component triggers the abort, and another cancels it unintentially. In theory, you should always do "rescue SomeSpecificExceptionType", but a lot of people do use just "rescue".

From: Evan Phoenix [mailto:evan at fallingsnow.net]
Sent: Monday, January 12, 2009 1:01 PM
To: ruby-core at ruby-lang.org
Subject: [ruby-core:21290] Re: MRI 1.8.6 bug - exit is ignored if ensure clause throws exception which is caught by outer rescue


On Jan 12, 2009, at 12:31 PM, Shri Borde wrote:

The following code snippet does print "after foo" when using MRI 1.8.6 on Windows Vista, showing that exit is ignored. Any thoughts on whether this is by design, a known bug, or a new issue? If it's the latter, should I open a bug for it?

No, this is by design. Kernel#exit raises SystemExit, which the toplevel rescues and performs the actual exit. If you raise a new exception in the ensure. the SystemExit exception is never seen by the toplevel, and thus you don't get the exit.

This is used in a few places to cause exit to be ignored, or to allow a library to convert a SystemExit exception into something else (perhaps an IllegalOperation or something).

 - Evan Phoenix


def foo
  begin
    begin
      begin
        exit
      rescue
        puts "We never reach here"
      end
    ensure
      raise "exception from ensure"
    end
  rescue
    puts "We do reach here, which is unexpected"
  end
end

foo
print "after foo"

Thanks,
Shri


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