Re: [PHP-DEV] Bug #2167: configure incorrectly identifies flock() as available From: Lyndon Nerenberg (lyndon <email protected>)
Date: 08/26/99

>>>>> "Sascha" == Sascha Schumann <sascha <email protected>> writes:

    Sascha> I don't see any advantage in using our flock()
    Sascha> emulation over Solaris' fcntl() wrapper. Our wrapper
    Sascha> depends as well on fcntl().

If you're going to encapsulate the lock routines you should write a
single lock function, and use it. The problem with providing an
emulated flock is that people will often just call flock and assume
they are getting the real thing. Specifically, they may be assuming
that flock will work over NFS. This may not be the case if flock
actually wraps lockf or fcntl. And nobody is going to be expecting
the fcntl behaviour of releasing all locks on a file if *any*
descriptor pointing at that file goes away. When dealing with locks,
you must code to the actual interface being used. Doing otherwise
introduces incorrect behaviour that can be very difficult to
debug.

I didn't spot the flock wrapper in php_compat.c the first time around.
My intention for the patch was to make the code not use flock at all
on Solaris.

I realize this is a pain in the butt. The only really portable
solution (for UNIX), is to just write to the lowest common denominator
and use fcntl. It's braindead, but at least you don't get any surprises
(you have to code to the brokenness inherent in fcntl). In the long
term this has eliminated quite a few "side effect" bugs caused by
assuming true flock semantics in what turned out to be a fcntl-wrappered
environment.

If nothing else, if PHP *does* fall back to emulating flock over fcntl
(specifically), it would be useful to have a #warning in the compile
stating that using flock might not work as expected.

--lyndon 

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