threads/141198: src/lib/libc/stdio does not properly initialize
mutexes
Jeremy Huddleston
jeremyhu at apple.com
Thu Jan 7 15:50:05 UTC 2010
The following reply was made to PR threads/141198; it has been noted by GNATS.
From: Jeremy Huddleston <jeremyhu at apple.com>
To: John Baldwin <jhb at freebsd.org>
Cc: freebsd-threads at freebsd.org,
freebsd-gnats-submit at freebsd.org
Subject: Re: threads/141198: src/lib/libc/stdio does not properly initialize mutexes
Date: Thu, 7 Jan 2010 10:44:54 -0500
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On Jan 7, 2010, at 09:56, John Baldwin wrote:
>> vasprintf.c.patch:+ INITEXTRA(&f);
>> vdprintf.c.patch:+ INITEXTRA(&f);
>> vfprintf.c.patch:+ INITEXTRA(&fake);
>> vfwprintf.c.patch:+ INITEXTRA(&fake);
>> vsnprintf.c.patch:+ INITEXTRA(&f);
>> vsprintf.c.patch:+ INITEXTRA(&f);
>> vsscanf.c.patch:+ INITEXTRA(&f);
>> vswprintf.c.patch:+ INITEXTRA(&f);
>> vswscanf.c.patch:+ INITEXTRA(&f);
>=20
> Ah, ok. In our stdio at least these are all dummy files that are =
passed to
> internal stdio routines that never do any locking (e.g. __vfprintf() =
which
> does no locking vs vfprintf() which does use the mutex locks). I'm =
not sure
> if that is also true for Darwin, but in theory it should be as these =
file
> objects are all private stack variables that no other threads can gain =
a
> reference to, so no locking is needed.
Yeah, we're just being cautious with these changes. It takes one clock =
cycle and maintains the old (FBSD 7?) state of initializing the mutex =
during INITEXTRA in those dumies... just in case something gets added =
down the line which needs it.
If you're confident that won't be the case for FBSD, then I believe your =
initial patch is sufficient.
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