[ruby-core:98507] [Ruby master Feature#15277] at_exec

Issue #15277 has been updated by vihai (Daniele Orlandi).


I would like to add a use-case that I'm encountering right now.

I would like to call prctl(PR_SET_PDEATHSIG, ...) in order to ensure that a spawned process is always killed regardless of how cleanly the parent process exits. I couldn't do this in the parent because fork(2) clears such setting so I must be able to invoke prctl between fork and exec.

An alternative solution would be to add a callback to spawn's options to be called before exec.

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Feature #15277: at_exec
https://bugs.ruby-lang.org/issues/15277#change-85784

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
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There's currently no easy way to have code executed before a subsequent call to `exec`. One has to monkey-patch the builtin method.

I'd like to propose a new method `at_exec` that would be very similar to `at_exit`, except that the callbacks are triggered before the current process is replaced by the external command.

```
# This would output "Hello", "Bye", and "Foo"
at_exec { puts "Bye!" }
puts "Hello"
exec "echo Foo"
```

Use case: we roll our own in `DeepCover`. Some test suites will call `exec`, and we need to store our counters before that happens.



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