7 Dec
2024
7 Dec
'24
10:12 p.m.
On 7 Dec 2024, at 14:45, Henry Bent <henry.r.bent(a)gmail.com> wrote:
Interesting, thank you for the explanation. How was
file locking handled for DOS programs? Did it have some sort of internal call to
"share" or was there a more elegant method?
Well, as the Unix filesystem was connected to MS-DOS as a “network drive” it had
rudimentary opportunistic locking via the SMB protocol which I am not entirely sure
actually translated to anything on the Unix side. There was often data corruption when
writing from multiple MS-DOS sessions to the same file so the customer, who was
particularly keen on the reading from multiple terminals more than the writing, simply
decided that only one person could write into the inventory at one time. “Sneaker lock”?
Anyway, the port to native Unix was achieved in a couple of months, this was the ‘80s,
code was simple and you didn’t have three rows of obscure buttons, a menu on top, another
one to the side, etc. to be able to write a letter… Once we moved to Unix C-ISAM
implemented proper record-level locking in the library itself and the problem went away
(except for the inevitable code changes to handle C-ISAM saying “can’t access the record
as it is locked, try again later”).
Arrigo