CRR: 7034139: G1: assert(Thread::current()->is_ConcurrentGC_thread()) failed: only a conc GC thread can call this (S)

[Tony Printezis]

Thanks to John Cuthbertson for looking at this. I took his advice and 
I'm going to disable the forced overflow by default (by setting the 
default parameter to 0), but leave the code in as it's helpful. Latest 
version here:

http://cr.openjdk.java.net/~tonyp/7034139/webrev.2/

Tony

Tony Printezis wrote:
> Hi all,
>
> I'd still like a couple of code reviews for this. Here's the latest 
> version (I only rephrased a couple of comments, so if you're looking 
> at the earlier version already you can ignore this one):
>
> http://cr.openjdk.java.net/~tonyp/7034139/webrev.1/
>
> Tony
>
> Tony Printezis wrote:
>> Hi,
>>
>> Could I get a couple of people to look at this? (I'd like to push 
>> this this week if possible)
>>
>> http://cr.openjdk.java.net/~tonyp/7034139/webrev.0/
>>
>> The actual fix is reasonably small (leave / join the 
>> SuspendibleThreadSet only if we are in concurrent mode). Most of the 
>> changes are new infrastructure to cause a fixed number of overflows 
>> during marking (in non-product builds of course) to stress the 
>> overflow code. This was the only way I could reliably reproduce the 
>> failure. This did uncover a couple of extra issues which I also fixed:
>>
>> - If we overflow during remark we should not actually deal with it 
>> during remark but we should abort the remark pause and restart a 
>> concurrent mark phase. For some reason we were not doing that. I 
>> fixed that (for this I had to ensure that the overflow flag is not 
>> cleared when we exit the do_marking_step() method).
>> - Because we were clearing the overflow, it was also possible that 
>> the workers would deadlock (for that to happen a worker had to finish 
>> handling one overflow and immediately raise another one, so it was 
>> highly unlikely to occur in prcatice; good to find it and eliminate 
>> it though).
>>
>> I've already tested it, I'll run more tests overnight.
>>
>> Tony
>