Disable heap iteration for Shenandoah in SA

[Aleksey Shipilev]

On 11/28/18 6:59 PM, Aleksey Shipilev wrote:
> On 11/28/18 6:38 PM, Roman Kennke wrote:
>> As Per pointed out in reviews, we cannot safely iterate objects in SA,
>> because current implementation is size-based. This might just crash.
>> Let's do the same as ZGC for now and disable it, and revert the other
>> pieces.
>>
>> http://cr.openjdk.java.net/~rkennke/disable-sa-heapdump/webrev.00/
> 
> Comment is incorrect, should be "Shenandoah":
> 
>  372        // Operation (currently) not supported with ZGC. Print
> 
> Then what Zhengyu said, we can remove cell_header_size completely?

Also, wait. This screws up jstack and Java monitor detection, right? I vaguely remember we added
this to satisfy adopter's request for this feature. I wonder if we can somehow check that class
unloading is not enabled before traversing.

-Aleksey