Is it possible to mark java objects non-collectable from gc perspective to save on gc-sweep time?

Question

Is it possible to mark java objects non-collectable from gc perspective to save on gc-sweep time?

Something along the lines of http://wwwasd.web.cern.ch/wwwasd/lhc++

Answer 1

Quite simply, for you to be able to do this, the garbage collection algorithm would need to be aware of such a flag, and take it into account when doing its work.

I'm not aware of any of the standard GC algorithms having such a flag, so for this to work you would need to write your own GC algorithm (after deciding on some feasible way to communicate this information to it).

In principle, in fact, you've already started down this track - you're deciding how garbage collection should be done rather than being happy to leaving it to the JVM's GC algo. Is the situation you describe a measurable problem for you; something for which the existing garbage collection is insufficient, but your plan would work? Garbage collectors are extremely well-tuned, so I wouldn't be surprised if the "inefficient" default strategy is actually faster than your naively-optimal one.

(Doing manual memory management is tricky and error-prone at the best of times; managing some memory yourself while using a stock garbage collector to handle the rest seems even worse. I expect you'd run into a lot of edge cases where the GC assumes it "knows" what's happening with the whole heap, which would no longer be true. Steer clear if you can...)