RFR JDK-8022442: Fix unchecked warnings in HashMap

Remi Forax forax at univ-mlv.fr
Tue Aug 6 22:42:42 UTC 2013

On 08/07/2013 12:23 AM, Dan Smith wrote:
> On Aug 6, 2013, at 2:43 PM, Remi Forax <forax at univ-mlv.fr> wrote:
>> On 08/06/2013 11:11 PM, Dan Smith wrote:
>>> Please review this warnings cleanup.
>>> Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8022442 (not yet visible)
>>> Webrev: http://cr.openjdk.java.net/~dlsmith/8022442/webrev.00/
>>> —Dan
>> Hi Dan,
>> I've seen that you have introduce a common super interface for entry and tree node,
>> I suppose that  you check that there is no performance regression.
>> I wonder if an abstract class is not better than an interface because as far as I know
>> CHA implemented in hotspot doesn't work on interface
>> (but I may be wrong, there is perhaps a special optimization for arrays).
> To make sure I understand: your concern is that an aastore will be more expensive when assigning to a KeyValueData[] than to an Object[] (or even to SomeOtherClass[])?
> For what it's worth, all assignments to table[i] are statically known to be safe.  E.g.:
> Entry<K,V> next = (Entry<K,V>) e.next;
> ...
> table[i] = next;
> So surely a smart VM only does the check once?

I was thinking (dreaming) that the VM can do no check at all because 
most of the time, TreeNode is not loaded.

> Here are some other things that might be concerns, but don't apply here:
> - interface method invocations: there are no methods in the interface to invoke
> - checkcast to an interface: all the casts are to concrete classes (Entry, TreeBin, TreeNode)
> (There are some unchecked casts from KeyValueData to KeyValueData with different type parameters, but I assume these don't cause any checkcasts.)
> —Dan


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