RFR: 8196340: (coll) Examine overriding inherited methods in ArrayList and ArrayList.SubList

[Ivan Gerasimov]

Thank you Claes!

The mutator methods normally first update the modCount and then change 
the size of ArrayList.

Then, in other methods the modCount is copied to a local variable first, 
and after that the size is copied.

This is not true for equalsRange(List<?> other, int from, int to) when 
it is called from ArrayList.equals: the size is first copied to the 
argument and then the modCount is checked inside of equalsRange().  If 
the size and modCount are changed in between, then equals may produce a 
wrong results.

It seems to be more accurate to store this.modCount prior calling to 
equalsRange((List<?>) o, 0, size); and do 
checkForComodification(expectedModCount); after it is done.

Checking for modCount inside equalsRange() can probably be safely removed.

There's another call to equalsRange() from SubList.equals().  In this 
case checkForComodification(); is already called after calling to 
equalsRange(), so everything seems to be fine here.

With kind regards,

Ivan


On 5/14/18 6:37 AM, Claes Redestad wrote:
> Hi Ivan,
>
> right, checkForComodification() alone should be sufficient here.
>
> Updated in-place: http://cr.openjdk.java.net/~redestad/8196340/open.01/
>
> Thanks!
>
> /Claes
>
> On 2018-05-12 03:38, Ivan Gerasimov wrote:
>> Hi Claes!
>>
>> One thing I can't figure out is why both these two checks are necessary:
>>
>> 1303             checkForComodification();
>> 1304             root.checkForComodification(expectedModCount);
>>
>> The former compares the current root.modCount with the one at the 
>> time this subList was created.
>>
>> The later one compares the current root.modCount with the one at the 
>> time the method was called.
>>
>> If the later fails, wouldn't it imply the former should also have 
>> failed?
>>
>>
>> With kind regards,
>>
>> Ivan
>

-- 
With kind regards,
Ivan Gerasimov