Re: [rvm-research] Immix with a split mature space

Hi,

unfortunately I don't have much experience with writing or modifying garbage collectors. Apologies in advance if nothing of the following is helpful to you.

On 28.10.2016 20:11, Shoaib Akram wrote:
> I am modifying the generational variant of the Immix collector in JikesRVM as part of a research project. [...] Using a verbose level of 5, I observe that after the first full heap collection, objects have been copied from A to B as reported in the "After Collection" statistics. However, when the mutator threads resume after collection, JikesRVM terminates abruptly without printing the stack trace.  The last message reported in the logs is "[STWController: Resuming mutators…].” 
This sounds like you're using the garbage collector in a normal Jikes RVM. If you haven't done so already, you could try using the MMTk test harness to try to reproduce and fix the problem.

If you want to do this with Jikes RVM, I'd advise you to provide more context about the problem. For example, if the hardware trap handler actually gets called, you may be able to print out registers. If the VM hangs, it might still respond to SIGQUIT and dump the thread stack. If you need to figure out the exact point where the VM stops, you could try inserting an instruction that is guaranteed to fail. For example, you could produce a null pointer access or insert a failing instruction with Magic.

> Is it possible that the references being made by the mutator threads - once the full heap collection is finished - can’t be resolved anymore because of the presence of two mature spaces?
I'm not quite sure what you want to say. Updating reference fields when moving objects is the job of the collector and the code in the MMTK-VM interface. The only way that the VM "resolves" object references is by applying barriers as required by the collector.


Kind regards,

Erik Brangs

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