java - Concurrent Mark and Sweep algorithm details

Question

I am struggling to understand and get more details on the steps involved in CMS tenured collection cycles.

1. Initial Mark
2. Concurrent Mark
3. Concurrent pre-clean
4. Re-mark
5. Concurrent Sweep
6. Concurrent Reset

These steps are explained in lot of places in very short. But if I have to describe them in a class with diagrams and psuedo-examples where can I get that information from?

PS - I have searched extensively on Google, it throws up with a lot of textual stuff and jargon which I understand. But I am looking for a more animated explanation so that I can teach my audience.

These are some of the links which are popular, the 3rd one was very promising but it failed to explain the CMS in particular

1. http://www.infoq.com/articles/Java_Garbage_Collection_Distilled
2. http://www.oracle.com/technetwork/java/javase/gc-tuning-6-140523.html
3. http://www.cubrid.org/blog/dev-platform/understanding-java-garbage-collection/

---

Dear all, thanks for commenting and pointing me to some resources. I have tried to create a visual representation of the CMS steps, can you please let me know if this matches your understanding ?

Also I seem to be missing the Compacting step, which step does it belong to ?

Answer : Ok so compacting is not handled by CMS, instead it is delegated to full GC.

Answer 1

Starting java 1.5, there is another phase that is missed out is the "concurrent abortable preclean". It aims to delay the remark until there is a desired occupancy is achieved in the Eden space.

Other than that you are pretty much on track.

I suggest you look at this old oracle gc whitepaper and this step by step description of the CMS gc logs . It confirms the steps you have put in the images.

This blog post summarizes things well.