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Date: Fri, 12 May 2006 12:49:36 -0700
From: Brian Dessent <brian AT dessent DOT net>
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Subject: Re: Fwd: Got any 'fileno_unlocked'?
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Rick Hanson wrote:

> Thanks for the tip.  I already tried knocking off the '_unlocked'
> suffix.  Although it does compile, I wonder what kind of runtime
> trouble I'm going to get into, since I did notice, by scanning the
> code, that the programmer locks his own file, then appeals to
> 'fileno_unlocked'.  Also, there is no configure script to help.

I think you are misunderstanding the purpose of these functions.

It has nothing to do with file locking, but rather locking in the sense
of thread-safety.  A programmer can call the _unlocked version of a
number of functions when he is sure that the application only has one
thread, and avoid a very slight penalty of having to set a mutex before
modifying the data structures.

Therefore, calling the standard version instead of the _unlocked version
is just skipping this optimization and should work in all cases.  In
fact, if anything should be considered unsafe it is the _unlocked
function, which if used improperly will certainly cause harm, unlike the
standard functions.

Furthermore, these _unlocked functions are *not* standardized functions,
they are GNU extensions, and this means the programmer has made his code
unportable by assuming they exist without the aid of a configure test. 
This is a bad thing to do.

Brian

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