At 12:22 -0400 on 08/01/2006, Wayne Driscoll wrote about Re: Data set
ENQueues and DEQueues in Jobs:
I could see how a downgrade would be useful. For instance: I have a
resource shared. Now I need to update the resource, so I perform an
S->E. Now, I want to allow others to see the update, but I don't want
to allow an exclusive user to lock me out of the resource, so a E->S
change would allow this to happen.
This is, of course, assuming that you can get the exclusive lock (via
a S->E change) in the first place. Attempting this first change
requires that no-one also has the shared lock (or is waiting on the
queue until all the shared locks are released pending the acquisition
of the exclusive lock). Depending on how long it is before you need
the exclusive lock, it might be simpler to just start with it before
downgrading to shared (if this downgrade was allowed by ENQ - which
we know is not currently supported).
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