hg: jdk8/tl/jdk: 8008167: IdentityHashMap.[keySet|values|entrySet].toArray speed-up

Mike Duigou mike.duigou at oracle.com
Sun Feb 24 18:53:10 UTC 2013

Ouch, this would have been introduced by me.

I will check to see how this could have passed the pre-commit regression testing. I suspect that a regression test needs to be improved.


On Feb 24 2013, at 10:48 , Alan Bateman wrote:

> On 24/02/2013 15:49, Peter Levart wrote:
>> Hi Alan,
>> I checked and it seems all 3 IHM views [keySet|values|entrySet] have a fail-fast iterator implementation (IdentityHashMap.IdentityHashMapIterator) and all 3 are (were) using the iterator for .toArray implementations. So this patch tries to preserve the behavior when there is a concurrent modification (which is only possible from other thread and is illegal usage anyway since IHM is not thread-safe) while executing the toArray methods on the views...
>> Do you see something I don't see?
> My apologies, I see it does check the modification count in IdentityHashMapIterator.nextIndex.
> However, as this forced me to looks at the changes-set again then the copy loop in Values.toArray has caught by eye:
>             for (int si = 0; si < tab.length; si += 2) {
>                 if (tab[si++] != null) { // key present ?
>                     // more elements than expected -> concurrent modification from other thread
>                     if (ti >= size) {
>                         throw new ConcurrentModificationException();
>                     }
>                     a[ti++] = (T) tab[si]; // copy value
>                 }
>             }
> Looks like si is incrementing by 3 rather than 2 (which ironically will cause a CME later because there will be fewer elements copied than expected). 
> Do you concur? If so then we can create a bug to change this to test tab[si] and copy in tab[si+1].
> -Alan

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