Luca's meaningless thoughts  

Basic algorithms summary

by Leandro Lucarella on 2008- 08- 12 00:42 (updated on 2008- 08- 12 01:26)
tagged copying, d, dgc, en, intro, mark-compact, mark-sweep, moving, non-moving, rc, tracing - with 6 comment(s)

Let's make a little summary about the big categories of garbage collection algorithms:

Basic algorithms summary

The first branch is reference counting vs. tracing garbage collectors. For D, reference counting is a really complicated choice, because to be (seriously) considered, the compilar/language have to change pretty much. However, one can make some manual bookkeeping to evaluate if this method has considerable advantages over the other to see if that extra work worth the effort.

Tracing garbage collectors is the easy way to go in D. Tracing comes in two flavors: moving and non-moving. Again, moving is hard in D, because all sort of nasty stuff can be done, but a lot more doable than reference counting. In the non-moving field, the major option is the good ol' mark & sweep (the algorithm used by the actual D garbage collector).

Going back to the moving ones, there are two big groups: copying and mark-compact. I don't like copying too much because it need at least double the residency of a program (remember, we are trying not to waste memory =). Mark-compact have some of the advantages of copying without this requirement.

Note

This is just one arbitrary categorization. There are a lot of other categories based on different topis, like: pauses (stop-the-world, incremental, concurrent, real-time), partitioning (generational, connectivity-based), pointer-awareness (precise, conservative) and probably a lot more that I don't even know.