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Date: Wed, 10 Mar 2004 02:49:31 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Alexander Kabaev <ak03@gte.com>
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cc: John Birrell <jb@freebsd.org>
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cc: John Birrell <jb@cimlogic.com.au>
Subject: Re: cvs commit: src/lib/libc/stdio _flock_stub.c local.h
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On Mon, 8 Mar 2004, Alexander Kabaev wrote:

> On Tue, Mar 09, 2004 at 03:05:36PM +1100, John Birrell wrote:
> >
> > I'm not sure that I agree that applications are 'broken' when they
> > use things that are defined in the header file along with the FILE
> > structure itself.

It's a historical mistake that FILE is not opaque.

> I would like to see FILE to become transparent to applications and its
> definition moved to the libc-private header file with the specific
> purpose of making the hack you mentioned impossible.

This would pessimize even getc_unlocked() and putc_unlocked().  getc()
and putc() are now extern functions, but the old macro/inline versions
are still available as getc_unlocked() and putc_unlocked().  Simple
benchmarks for reading a 100MB file on an Athlon XP1600 overclocked
show that the function versions are up to 9 times slower:

Time to read the file from a disk cache using read(): 0.17 seconds (sys)
getc_unlocked() overhead: 0.41 seconds (user)
getc() overhead: 1.64 seconds (user)

This is with static linkage.  Dynamic linkage increases the getc()
pessimization significantly:

read() time: no significant change
getc_unlocked() overhead: 0.44 seconds (user)
getc() overhead: 3.62 seconds (user)

Bruce

Bruce