From: KOSAKI Motohiro <kosaki.motohiro@...>
Date: 2011-02-15T19:38:03+09:00
Subject: [ruby-core:35248] Re: [Ruby 1.9-Bug#4400][Open] nested at_exit hooks run in strange order

2011/2/15 Suraj Kurapati <redmine@ruby-lang.org>:
> Bug #4400: nested at_exit hooks run in strange order
> http://redmine.ruby-lang.org/issues/show/4400
>
> Author: Suraj Kurapati
> Status: Open, Priority: Normal
> Category: core
> ruby -v: ruby 1.9.2p136 (2010-12-25 revision 30365) [x86_64-linux]
>
> Hello,
>
> The documentation for Kernel#at_exit says "If multiple [at_exit] handlers are
> registered, they are executed in reverse order of registration". �However, does
> not seem to be true for nested at_exit hooks (registering an at_exit hook inside
> another at_exit hook). �For example consider this code:
>
> at_exit { puts :outer0 }
> at_exit { puts :outer1_begin; at_exit { puts :inner1 }; puts :outer1_end }
> at_exit { puts :outer2_begin; at_exit { puts :inner2 }; puts :outer2_end }
> at_exit { puts :outer3 }
>
> Here is the output of running this code with two Rubies:
>
> ruby 1.9.2p136 (2010-12-25 revision 30365) [x86_64-linux]
> outer3
> outer2_begin
> outer2_end
> outer1_begin
> outer1_end
> outer0
> inner1
> inner2
>
> ruby 1.8.7 (2010-08-16 patchlevel 302) [x86_64-linux]
> outer3
> outer2_begin
> outer2_end
> outer1_begin
> outer1_end
> outer0
> inner1
> inner2
>
> Observe how inner1 and inner2 are executed in registration order after all
> non-nested hooks are executed in reverse registration order. �This seems very
> strange to me; I would expect nested at_exit hooks to be executed immediately
> (as follows) because we are already inside the at_exit phase of the program:
>
> outer3
> outer2_begin
> inner2
> outer2_end
> outer1_begin
> inner1
> outer1_end
> outer0
>
> What do you think? �Thanks for your consideration.

btw, C's atexit() has different behavior.

at_exit.c
------------------------------------------------------------------
#include <stdlib.h>
#include <stdio.h>

static void func0(void) { printf("outer0\n"); }

static void func1_inner(void) { printf("inner1\n"); }

static void func1(void)
{
        printf("outer1_begin\n");
        atexit(func1_inner);
        printf("outer1_end\n");
}

static void func2_inner(void) { printf("inner2\n"); }

static void func2(void)
{
        printf("outer2_begin\n");
        atexit(func2_inner);
        printf("outer2_end\n");
}

static void func3(void) { printf("outer3\n"); }

main()
{
        atexit(func0);
        atexit(func1);
        atexit(func2);
        atexit(func3);
}
------------------------------------------------------------------

% gcc at_exit.c; ./a.out
outer3
outer2_begin
outer2_end
inner2
outer1_begin
outer1_end
inner1
outer0