Re:Garbage Collection
by nostrademons on Saturday November 30, 2019 @07:50PM
(#21673065)
There's a classic paper that shows that refcounting and GC are in fact duals of each other, where GC is effectively tracing live objects and refcounting is tracing dead objects:
This had a number of important corollaries to this. One is that they have opposite performance characteristics: GCs make creating new references fast but then create a large pause when RAM is exhausted and a collection happens, while refcounts make creating new references slow and create a large pause when large object graphs are freed all at once. Another is that nearly all high-performance memory management systems are hybrids of the two: lazy refcounting is basically like implementing a local garbage collector and then feeding the live set of that into the refcounts, while generational garbage collection is like implementing a local refcount (the write barrier) and feeding the results of that into the root set.
https://dl.acm.org/citation.cfm?id=1028982
This had a number of important corollaries to this. One is that they have opposite performance characteristics: GCs make creating new references fast but then create a large pause when RAM is exhausted and a collection happens, while refcounts make creating new references slow and create a large pause when large object graphs are freed all at once. Another is that nearly all high-performance memory management systems are hybrids of the two: lazy refcounting is basically like implementing a local garbage collector and then feeding the live set of that into the refcounts, while generational garbage collection is like implementing a local refcount (the write barrier) and feeding the results of that into the root set.