Useful at_exit idiom

i’m constantly struggling with the fact that children need to use exit!
to
prevent exit handlers registered in the parent being called twice, for
example:

harp:~ > cat a.rb
at_exit{ puts ‘parent’ }

fork{
at_exit{ puts ‘child’ }
} and Process.wait

harp:~ > ruby a.rb
child
parent
parent

arggh. this is a neat work-around:

harp:~ > cat a.rb
at_exit{ puts ‘parent’ }

fork{
at_exit{ exit! }
at_exit{ puts ‘child’ }
} and Process.wait

harp:~ > ruby a.rb
child
parent

i’m sure i’m not the first one to think of this, but it sure is handy to
separate the parent’s handlers from the child’s… anyone see issues
with
this?

-a

Hi,

In message “Re: useful at_exit idiom”
on Tue, 10 Oct 2006 13:21:21 +0900, [email protected] writes:
|

|i’m constantly struggling with the fact that children need to use exit! to
|prevent exit handlers registered in the parent being called twice,

|i’m sure i’m not the first one to think of this, but it sure is handy to
|separate the parent’s handlers from the child’s… anyone see issues with
|this?

linux man atexit(3) says:

  When a child process is created via fork(), it inherits copies
  of the its parents registrations.  Upon a successful call to one
  of the exec() functions, all registrations are removed.

so I think this is expected behavior for most of the cases, since Ruby
inherits many behaviors from C libraries.

						matz.

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