Re: Injection point locking

On Tue, Jul 09, 2024 at 12:12:04PM +0300, Heikki Linnakangas wrote:
> I thought about it, but no. If the generation number doesn't match, there
> are a few possibilities:
> 
> 1. The entry was what we were looking for, but it was concurrently detached.
> Return NULL is correct in that case.
> 
> 2. The entry was what we were looking for, but it was concurrently detached,
> and was then immediately reattached. NULL is a fine return value in that
> case too. When Run runs concurrently with Detach+Attach, you don't get any
> guarantee whether the actual apparent order is "Detach, Attach, Run",
> "Detach, Run, Attach", or "Run, Detach, Attach". NULL result corresponds to
> the "Detach, Run, Attach" ordering.
>
> 3. The entry was not actually what we were looking for. The name comparison
> falsely matched just because the slot was concurrently detached and recycled
> for a different injection point. We must continue the search in that case.
> 
> I added a comment to the top of the loop to explain scenario 2. And a
> comment to the "continue" to explain scnario 3, because that's a bit subtle.

Okay.  I am fine with your arguments here.  There is still an argument
imo about looping back at the beginning of ActiveInjectionPoints
entries if we find an entry with a matching name but the generation
does not match with the local copy for the detach-attach concurrent
case, but just moving on with the follow-up entries is also OK by me,
as well.

The new comments in InjectionPointCacheRefresh() are nice
improvements.  Thanks for that.
--
Michael