Array ring buffer wastes capacity

[franz1981]

After eons I wanted to reuse this structure for http 2 stream handling in Netty and..

jgroups-raft/src/org/jgroups/raft/util/ArrayRingBuffer.java

Line 269 in a31940e

headSequence++;

Doesn't seem to account for gaps 😕

i.e.

1. Add 3 elements
2. Remove with index the first 2 inserted: head sequence is still there but we have null out two slots
3. Remove the last and observe that we won't get back anymore the full capacity although all 4 elements are gone

Remove should keep on checking bubbles of nulls to move the head as much as it can, till the tail, if necessary (or stopping at the first non null).

[jabolina]

Hello, @franz1981. We've also included it on ISPN recently (infinispan/infinispan#13016). I think Will has also added a few modifications.

[franz1981]

Nice one, but the issue is valid? I have read it on the phone since today I couldn't use the computer, so I could be very wrong

[wburns]

Yeah, I implemented this in our version of the ArrayRingBuffer as I didn't want to deal with the empty space. Check the catchUpHeadPointer method on the PR above.

Maybe there is a more efficient way of doing it, instead of having the while loop, but it seems to work as it is.

[franz1981]

@wburns
I have this version I implemented for Netty, simplified: https://gist.github.com/franz1981/6277af990ccfe0a5da8542a75d66ce5e

let me know if it can be of any help

and thanks for infinispan/infinispan#13016: has made my day, seeing this little one been used elsewhere ❤️