RFR(xs): 8145192: 'count' variable can overflow in PSMarkSweep::invoke on 64 bit JVM

[sangheon]

Hi Tom,

Thank you for reviewing this.

On 01/22/2016 12:52 PM, Tom Benson wrote:
> Hi,
> I think it would be *slightly* more logical to instead reduce 
> MarkSweepAlwaysCompactCount to a uint, since there should be no need 
> for it to be anywhere near even that large. 
Okay, I will fix.
I considered change the flag to 'uint' as well but I selected this 
approach as this is simpler. :)

> But I don't feel too strongly, and that would require changing the test.
I ran TestGCOld.java to trigger enough GCs and it was fine.

Let me post a new webrev after testing JPRT on Monday.

* I have one thing to note: JDK-8144578 is on review and its patch 
contains to exclude testing this flag from TestOptionsWithRanges.java. 
So if 8144578 is pushed earlier than this, I should revise this patch.

Thanks,
Sangheon


>
> So, the change looks OK to me.
> Tom
>
> On 1/22/2016 2:56 PM, sangheon wrote:
>> Hi all,
>>
>> Could I have reviews for this tiny change to avoid zero division?
>>
>> 'uintx' type flag 'MarkSweepAlwaysCompactCount' is used to set 'uint' 
>> type local variable and this would result in an overflow for big 
>> numbers(>max_juint).
>> As a solution, this local variable should be changed to 'uintx'.
>>
>> I didn't add a new test as JDK-8144578 enables to check this problem.
>>
>> CR: https://bugs.openjdk.java.net/browse/JDK-8145192
>> Webrev: http://cr.openjdk.java.net/~sangheki/8145192/webrev.00
>> Testing: JPRT, manual test[1]
>>
>> [1]: Call System.gc() with VM option of '-XX:+UseParallelGC 
>> -XX:-UseParallelOldGC -XX:MarkSweepAlwaysCompactCount=4294967296' 
>> (=max_juint + 1).
>>
>> Thanks,
>> Sangheon
>