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

Alan Bateman Alan.Bateman at oracle.com
Sun Feb 24 18:48:58 UTC 2013

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 

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 

Do you concur? If so then we can create a bug to change this to test 
tab[si] and copy in tab[si+1].


More information about the core-libs-dev mailing list