Re: [9fans] new system calls - semacquire, semrelease

[Charles Forsyth <forsyth@terzarima.net>]

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here's a different little hack that's more unix-specific,
which i borrowed from unix libthread (i think that's where i saw it,
although it might be well-known in fcntl land).

a parent process needs to know whether a child has successfully done an exec
of an arbitrary program (so it's hard to have that program tell the parent).
the parent makes a pipe, marks the child's end as close-on-exec, forks, and then
reads its end of the pipe.  if the exec succeeds, the read returns 0; if the
exec fails, the child writes the diagnostic on the pipe, so again the read returns something.

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From: "Bruce Ellis" <bruce.ellis@gmail.com>
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu>
Subject: Re: [9fans] new system calls - semacquire, semrelease
Date: Mon, 27 Mar 2006 03:11:45 +1000
Message-ID: <775b8d190603260911h73f5b3ceqb03c5724ab95f6fb@mail.gmail.com>

boyd would put keys in pipes so core dumps (incidental or nasty)
wouldn't give them away.  interesting to think about, given my
current plumbing problems (water not bytes).

brucee

On 3/26/06, Lyndon Nerenberg <lyndon@orthanc.ca> wrote:
>
> On Mar 25, 2006, at 8:12 AM, Russ Cox wrote:
>
> > much like the old trick of storing a byte in a pipe
> > and using it as an interprocess lock.
>
> It's a brilliant trick. It let us write some very portable code (to
> windows, too, no less) with almost no effort.  Don't knock
> inginuity.  (Or insanity.  But that's just labels ...)
>
> --lyndon
>