Ironruby core - Jan 2009 - MRI 1.8.6 bug - exit is ignored if ensure clause throws exception which is caught by outer rescue

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?

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://rubyforge.org/pipermail/ironruby-core/attachments/20090112/b4ad4e0d/attachment.html>

I believe this is by design. Exit throws an exception (SystemExit). The
exception is not rescued by a default rescue clause because it doesn''t
derive from StandardError. Thus the raise in ensure gets called and it raises
RuntimeError which gets caught in the outer rescue because RuntimeError <:
StandardError.

Tomas

From: Shri Borde [mailto:Shri.Borde at microsoft.com]
Sent: Monday, January 12, 2009 12:32 PM
To: ironruby-core at rubyforge.org; ruby-core at ruby-lang.org
Subject: [ruby-core:21289] MRI 1.8.6 bug - exit is ignored if ensure clause
throws exception which is caught by outer rescue

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?

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://rubyforge.org/pipermail/ironruby-core/attachments/20090112/eec33e3d/attachment.html>

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


-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://rubyforge.org/pipermail/ironruby-core/attachments/20090112/0669a02f/attachment.html>

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


-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://rubyforge.org/pipermail/ironruby-core/attachments/20090112/8401b9c9/attachment.html>