Design #787
Remove refcounts from RingElem?
Description
Ref counts tend to work badly in multithreaded environments (since the incr/decr operations have to be atomic, and/or lock out other threads).
Having a refcount in each RingElem implies very many incr/decr operations; this is probably undesirable in a multithreaded setting.
On the other hand, the refcounts do let us know when a ring is no longer needed, so it can be automatically destroyed.
How feasible is it to remove the refcounts from RingElem?
Related issues
History
#1
Updated by Anna Maria Bigatti over 8 years ago
Updated by So far we've been creating rings for temporary computations without worrying too much (indeed: starting every time with a clean block of memory seems to improve locality, encouraging to create new rings!)
Not clearing the memory could have a bad effect on memory consumption. :-(
#2
Updated by John Abbott over 8 years ago
Updated by The comment about memory consumption is partly related to issue #786; if the "waste" per ring is small enough, it may not matter too much. For instance, if you have 1000 "idle" rings, and each ring has acquired just 4Kbytes then that's a total of about 4Mbytes lying idle... not ideal, but not too bad either.
A more worrying aspect is that the current implementation of MemPool never releases memory; if you do a big computation (in some) at the start, and then throw it all away, the MemPool for that ring will continue to hold onto the memory acquired for the big computation even though it is no longer needed.