Request for review (S): 8006242: G1: WorkerDataArray<T>::verify() too strict for double calculations

John Cuthbertson john.cuthbertson at oracle.com
Tue Jan 15 17:59:44 UTC 2013


Hi Bengt,

Changes look good to me. Minor nits:

Copyrights need updating.
Use UINT32_FORMAT instead of %d in the error message.
Check the indentation of the for loop in G1GCPhaseTimes::note_gc_end().

JohnC

On 1/14/2013 1:06 PM, Bengt Rutisson wrote:
>
> Hi all,
>
> Could I have a couple of reviews for this small change?
> http://cr.openjdk.java.net/~brutisso/8006242/webrev.00/
>
> Thanks to John Cuthbertson for finding this bug and providing 
> excellent data to track down the issue.
>
> From the bug report:
>
> In non-product builds the WorkerDataArrays in G1 are initialized to -1 
> in WorkerDataArray<T>::reset() when a GC starts. At the end of a GC 
> WorkerDataArray<T>::verify() verifies that all entries in a 
> WorkerDataArray has been set. Currently it does this by asserting that 
> the entries are >= 0. This is fine in theory since the entries should 
> contain counts or times that are all positive.
>
> The problem is that some WorkerDataArrays are of type double. And some 
> of those are set up through calculations using doubles. If those 
> calculations result in a value close to 0 we could end up with a value 
> slightly less than 0 since double calculations don't have full precision.
>
> All we really want to verify is that all the entries were set. So, it 
> should be enough to verify that entries do not contain the value set 
> by the reset() method.
>
> Bengt

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