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From: "Elliot Mednick" <elliot AT lexra DOT com>
To: "Cygwin AT Sourceware. Cygnus. Com" <cygwin AT sourceware DOT cygnus DOT com>
Subject: Re: mmap() for shared memory? 
Date: Wed, 7 Jun 2000 21:53:13 -0400
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> Where are you getting the memory from?  mmap has to be given something
> to map - it doesn't create memory out of thin air.  Normally you give
> it an open file to map; the only "empty" file is /dev/zero and that's
> not shared anyway.

Thanks for your response.  I'm pretty sure I'm calling mmap correctly.  I'm
mapping a file and I can see the file being modified afterwards.  The
problem is that the client side never sees the change.  It's almost like
there is some disconnect, like the MAP_SHARED parameter didn't "take".

There was a posting in January with a similar problem which included an
example that worked under real Unix but not under Cygnus; I tried it and
couldn't get it to work either with the latest stuff (1.1.2 dll).

>> Perhaps someone can suggest the optimal IPC mechanism under Cygwin.

> The optimal IPC is, well, IPCs, stuff like shmget().  Unfortunately,
> cygwin doesn't support those.

I looked at Ludovic Lang's Cygwin IPC package, but it uses mmap, so it
doesn't buy me anything (except compatibility with shm).  And it uses a
daemon, which gets in the way for what I need this for.


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