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From: Bruno Haible <bruno@clisp.org>
To: bug-gnulib@gnu.org
Cc: Paul Eggert <eggert@cs.ucla.edu>
Subject: single-threaded optimizations
Date: Wed, 03 Mar 2021 04:27:56 +0100	[thread overview]
Message-ID: <14551115.F8Qjx3YMge@omega> (raw)
In-Reply-To: <20210303002855.5819-1-eggert@cs.ucla.edu>

Hi Paul,

Paul Eggert wrote:
> +       * lib/mbtowc-lock.h (mbtowc_with_lock) [USE_UNLOCKED_IO]:
> +       Don’t bother with locks, since this app is single-threaded.

We now have two C macros which indicate a single-threaded application:

* USE_UNLOCKED_IO, used
    - for unlocked <stdio.h>
    - in regex
    - in mbrtowc
* GNULIB_WCHAR_SINGLE, used in wcwidth.

This gets weirder over time.

Should we have one macro for each of gnulib's facilities (stdio, regex,
multibyte/wchar)?

Or should we have one macro in general? In this case I would suggest
to choose a more generic name, instead of USE_UNLOCKED_IO.

Recall that a general macro won't cut it e.g. for coreutils. coreutils
has multithreaded programs ('sort') next to single-threaded programs.
But coreutils wants to optimize wcwidth. GNULIB_WCHAR_SINGLE actually
means "assume that the locale has been set before the program becomes
multithreaded, and won't change afterwards". Similarly,
'#include "unlocked-io.h"' does not mean that the program is single-
threaded; it means that no FILE object is being accessed in more than
one thread.

What do you think?

Bruno



  reply	other threads:[~2021-03-03  3:28 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-03  0:28 [PATCH] mbrtowc: port to AIX 7.1 with xlc 12.1 Paul Eggert
2021-03-03  3:27 ` Bruno Haible [this message]
2021-03-06 16:56   ` single-threaded optimizations Paul Eggert
2021-03-07  9:58     ` Bruno Haible
2021-03-07 10:03       ` Bruno Haible
2021-03-08  2:46       ` Paul Eggert

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