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bug#23963: 25.0.95; Feature request: setup-unwind-protect, complementing
From: |
Markus Triska |
Subject: |
bug#23963: 25.0.95; Feature request: setup-unwind-protect, complementing unwind-protect |
Date: |
Wed, 13 Jul 2016 08:28:45 +0200 |
The manual entry of `unwind-protect' shows an example whose essence is:
(unwind-protect
(progn
(setq process (ftp-...))
;; use process
(delete-process process))
It adds the following important explanation:
This example has a small [sic] bug: if the user types `C-g' to quit,
and the quit happens immediately after the function `ftp-...'
returns but before the variable `process' is set, *the process will
not be killed*. There is no easy way to fix this bug, but at least
it is very unlikely.
Would it be good to make such resource leak *impossible* instead? This
seems quite desirable and could be done with a complementing primitive.
Please consider a new primitive `setup-unwind-protect' with 3 arguments:
1. SETUPFORM, called in such a way that it *cannot be interrupted*
2. BODYFORM, like in unwind-protect, called after SETUPFORM
3. UNWINDFORMS, like in unwind-protect
With this primitive, we could write the example above as:
(setup-unwind-protect
(setq process (ftp-...))
(progn
;; use process ...
(delete-process process))
Please consider adding such a construct to Emacs.
A precedence for such a construct is setup_call_cleanup/3 which appears
in the Prolog ISO draft standard and is already included in many systems:
https://www.complang.tuwien.ac.at/ulrich/iso-prolog/N215
Thank you and all the best!
Markus
In GNU Emacs 25.0.95.4 (x86_64-apple-darwin15.5.0, X toolkit, Xaw scroll bars)
of 2016-07-05 built on mt-imac
Repository revision: e3b039d1a0e611d6619ed3ce67d125160d644ebc
Windowing system distributor 'The X.Org Foundation', version 11.0.11502000
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LDFLAGS=-L/opt/local/lib'
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