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From: dkeisen@Gang-of-Four.Stanford.EDU (Dave Eisen)
Newsgroups: comp.unix.xenix.sco
Subject: Re: Shared Memory on SCO Xenix
Keywords: shmem Xenix
Message-ID: <1990Oct7.010652.29884@Neon.Stanford.EDU>
Date: 7 Oct 90 01:06:52 GMT
References: <1589@pscnet.UUCP>
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In article <1589@pscnet.UUCP> kean@pscnet.UUCP (Kean Johnston) writes:
>Please could someone clarify a point for me relating to shared memory under
>SCO Xenix, specifically Xenix/386 release 2.3.2 or 2.3.3.
>In his excelent book "Advanced Unix Programming" by Marc J. Rochkind,
>in the chapter on IPC's and shared memory he states that under Xenix, after
>having mapped a segment as shared, you have to unmap it before you can
>issue any system calls. This means that you have to keep on mapping and
>unmapping the shared data segment each time you need to make a system call.
>Is this still true of Xenix, or is the book just outdated. It WAS written
>6 years ago after all.

It's outdated. We attach a couple of segments of shared memory at the
start of essentially all of our programs and use it as ordinary memory.

if you do use it, I should mention one difficulty we've had with it.
There is a bug in the implementation of shared memory in 2.2.3 (it may 
have disppeared in 2.3.2, we've never tested) forced us to allocate a few 
extra bytes at the end of a shared memory segment or else accessing the
last byte caused a program crash.



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