I spent some time looking at this patch today and found that a good deal of cleanup work seemed to be needed. Attached is a cleaned-up version which makes a number of changes:
I'm not entirely happy with the name "nextClearXidElem" but apart from that I'm fairly happy with this version.
Can we just call it "nextAtomicListElem" and the one in PROC_HDR "headAtomicList" or something like that? Basically we can use the same list later at other places requiring similar treatment. I don't see them anything specific to clearXid stuff. Rather it is just some sort of atomic list of PGPROC
I actually even thought if we can define some macros or functions to work on atomic list of PGPROCs. What we need is:
- Atomic operation to add a PGPROC to list list and return the head of the list at the time of addition
- Atomic operation to delink a list from the head and return the head of the list at that time
- Atomic operation to remove a PGPROC from the list and return next element in the list
- An iterator to work on the list.
This will avoid code duplication when this infrastructure is used at other places. Any mistake in the sequence of read/write/cas can lead to a hard to find bug.
Having said that, it might be ok if we go with the current approach and then revisit this if and when other parts require similar logic.
