A rename operation can be used instead of O_EXCL|O_CREAT to serve an a file
semaphore, i.e.:

1) Create a permanent file with a process-unique name, i.e. foobar.[mypin] or
somesuch.

2) Attempt to rename the above file to "foobar".

3) If the rename fails, foobar must already exist, and so somebody else has
control of the semaphore.

4) If the rename succeeded, you now have control of the semaphore.

Of course, you must also add in code to handle the case of what happens when
the process holding the semaphore file aborts and leaves the file laying around.

- Mark B. (catching up on HP3000-L backlog)

Jeff Woods wrote:

> Mark Bixby wrote:
>
>>Are you linking with MPE libc or POSIX libc?
>>
>>I definitely know this works with POSIX libc because I have
>>seen it in various ports of mine.  I have never tried to do
>>it with MPE libc though.
>>
>
> I'm using LIBCSHR.LIB.SYS, LIBCANSI.LIB.SYS (plus a few others including
> SOCKETRL.NET.SYS) all on MPE 7.0(Exp1).  It's my understanding that the
> POSIX routines only support bytestream files and this program needs to
> access (and create) non-bytestream (actually Variable-ASCII "VA") files
> and work smoothly from the CI in a jobstream.
>
> P.S.  I've already recoded the I/O to use sprintf() for formatting and
> HPFOPEN(), FWRITE() and FCLOSE() intrinsics for accessing the file, so I
> don't actually need an answer for this situation anymore.  (But if
> something comes along that lets me convert the couple of dozen printf()
> calls from something like this:
>
>         sprintf(log_buff, "Send(%s) errno=%d", buff, errno);
>         mpe_FWRITE(log_fnum, log_buff, -strlen(log_buff), 0);
>
> .... back to something like this:
>
>         printf(log_file, "Send(%s) errno=%d\n", buff, errno);
>
> .... I'd be inclined to spend the time.)
>
> Thanks.
> --
> Jeff Woods
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> Quintessential School Systems
>
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>


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