Odd error

[Kenneth Brody]

Quoting Doug Luurs (Tue, 18 Dec 2007 08:40:25 -0500):

> In my 25+ years of programming in filepro, I have never seen this one ..
> Anyone every see it, or have
> an idea what caused it ?
>
> User was going into IUA (dclerk) using a normal Index selection (Index A -
> One field, 6 characters-Nothing fancy)
> *
> Fatal error
> /appl/filepro/payables/index.A: Deadlock situation detected / avoided.
>
> screen ,1
>
> *Program worked fine once we hit ENTER and tried the same lookup again.
> *
> *I am thinking it the program was having one of those senior moments.
> (Similar to us old farts)*

A deadlock situation is one in which two (or more) processes would end up
waiting forever.  For example, process A has record 1 locked, and process
B has record 2 locked.  Then, process A attempts to lock record 2 (meaning
that it needs to wait for process B to unlock it).  Finally, process B
attempts to lock record 1, meaning that it needs to wait for process A to
unlock it.  If this were to be allowed, the lock request could never be
satisfied, as A will never release the lock, as it's waiting for B to
release its lock.  (The same can happen with more than two processes, as
long as there is a loop, with the result being that the processes would
all end up waiting forever.  For example, A has 1 locked, and is waiting
for 2, which is locked by B, which is waiting for 3, which is locked by C,
which is waiting for 4, which now wants to lock 1.)

My understanding is that there is another situation in which the O/S will
give this error code, and that's if the system-wide limit on locks has
been reached.  (ie: there is no "too many locks" error, and a deadlock
error is returned in its stead.)

-- 
KenBrody at BestWeb dot net        spamtrap: <g8ymh8uf001 at sneakemail.com>
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