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Date:      Wed, 17 Feb 1999 21:36:22 -0700
From:      Warner Losh <imp@village.org>
To:        Matthew Dillon <dillon@apollo.backplane.com>
Cc:        hackers@FreeBSD.ORG
Subject:   Re: portability of shm, mmap, pipes and socket IPC 
Message-ID:  <199902180436.VAA64812@harmony.village.org>
In-Reply-To: Your message of "Wed, 10 Feb 1999 01:07:44 PST." <199902100907.BAA79553@apollo.backplane.com> 
References:  <199902100907.BAA79553@apollo.backplane.com>  <199902092246.PAA10658@usr02.primenet.com> <199902100403.MAA55849@spinner.netplex.com.au> <19990210085847.A11710@gil.physik.rwth-aachen.de> 

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In message <199902100907.BAA79553@apollo.backplane.com> Matthew Dillon writes:
:     The problem is that linux updates the timeval structure on return,
:     telling you how much time is left.

Linux is the only system to do this.  And it was flawed because if
there is an interrupt that causes a higher priority process to run,
the value is too small.  The value is only an approximation.

:     Many programs assumed that tv was const... i.e. not modified by
:     the call, and so would initialize the structure once then use it
:     multiple times.

It was before Linux.

:     I don't know what linux does now, but most programs these days 
:     reinitialize tv on each select() call in order to work around
:     any potential problem.

Linux's system call still modifies things.  However, there is a
bsd_select in most libraries that does the right thing, at least the
thing that all other oses do.

Warner


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