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| From: | Paul Eggert |
| Subject: | Re: single-threaded optimizations |
| Date: | Sat, 6 Mar 2021 08:56:40 -0800 |
| User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 |
On 3/2/21 7:27 PM, Bruno Haible wrote:
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.
Good point. How about this idea?* We establish a new macro GNULIB_MBTOWC_SINGLE which means "assume that at most one thread invokes mbtowc-like functions". The mbtowc replacement uses this instead of using USE_UNLOCKED_IO. Tar can #define this new macro.
* If macros like GNLIB_MBTOWC_SINGLE proliferate, we can have a single macro GNULIB_SINGLE_THREADED that implies all the other macros. For now I'm not sure it's worth the bother to do this.
* If someone has the time, fix the underlying problem that the Gnulib mbrtowc replacement doesn't link under AIX in some circumstances, unless you #define GNULIB_MBTOWC_SINGLE. I'm not sure exactly what these circumstances are, and anyway if I were to delve into that, I think I might want to investigate the possibility of having the mbrtowc replacement use AIX mbrtowc instead of a lock around AIX mbtowc, as that should perform better anyway. But I'm not sure AIX is worth the time for this sort of thing.
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