>> >> You can't open a file both long-mapped
>> >>and short-mapped: if one process opens a file long-mapped, all other
>Well, you can ... (see Beyond RISC! for the full table), but the
>bottom line is:
>   if the first accessor opens it short-mapped, then a subsequent long-mapped
>   open will work ... you'll get a 64-bit address (and, if you look, the
>   upper 32 bits will be either hex $a or hex $b, and the bottom 32 bits
>   will be a large number ($80000000..$ffffffff)).
 
We did an interesting experiment once to see how MPE comes up with the
address for mapped files. Apparently, the memory address for mapped files
comes from the physical location of the file on disk.
 
We had a program open a file mapped, and report the returned address. We
noticed that when several different programs opened the file they all got
the same address!
 
Reboot the HP, and the returned address on the file is still the same.
 
If I remember, even renames didn't change the address -- even across
accounts. The only thing that would change the returned address of the
mapped file was a file copy, or a purge and rebuild of the file. (Makes sense)
 
Pretty revealing into how MPE handles mapped files internally, no?
 
-Dan
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|Dan Hollis -- Pharmacy Computer Services, Inc.|
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