RFR [9] 8151384: Examine sun.misc.ASCIICaseInsensitiveComparator

[Chris Hegarty]

On 9 Mar 2016, at 14:43, Peter Levart <peter.levart at gmail.com> wrote:

> 
> On 03/09/2016 02:44 PM, Chris Hegarty wrote:
>> On 9 Mar 2016, at 13:03, Claes Redestad <claes.redestad at oracle.com> wrote:
>> 
>>> On 2016-03-09 13:17, Peter Levart wrote:
>>>>> When digging through old history to try to find out why java.util.jar.Attributes
>>>>> was ever using ASCIICaseInsensitiveComparator, it was not clear that
>>>>> performance was the motivation.
>>>> I guess looking-up a manifest attribute is not a performance critical operation, you are right.
>>> Could this be an old startup optimization, since first call to String.toLowerCase/toUpperCase will initialize and pull in java.util.Locale and friends? If so it's probably not effective any more.
>>> 
>>> Coincidentally - due to a recent regression - we're currently spending quite a bit of time parsing manifests of all jar files on the classpath, making ASCIICaseInsensitiveComparator show up prominently in some startup profiles.
>> Not any more ( it is no longer with us )!!
>> 
>> Interesting… let me know if you issues once this change makes its
>> way into a promoted build, or during your performance investigations.
>> 
>> BTW. I am not against doing something “smarter” for Attributes.hashCode.
>> I just didn’t think it was relevant, or performance sensitive, any more.
>> 
>> -Chris
> 
> Hi Chris,
> 
> I have another concern. Let's say Attributes keys are LATIN1. So for comparison, the StringLatin1.compareToCI is used:
> 
>    public static int compareToCI(byte[] value, byte[] other) {
>        int len1 = value.length;
>        int len2 = other.length;
>        int lim = Math.min(len1, len2);
>        for (int k = 0; k < lim; k++) {
>            if (value[k] != other[k]) {
>                char c1 = (char) CharacterDataLatin1.instance.toUpperCase(getChar(value, k));
>                char c2 = (char) CharacterDataLatin1.instance.toUpperCase(getChar(other, k));
>                if (c1 != c2) {
>                    c1 = (char) CharacterDataLatin1.instance.toLowerCase(c1);
>                    c2 = (char) CharacterDataLatin1.instance.toLowerCase(c2);
>                    if (c1 != c2) {
>                        return c1 - c2;
>                    }
>                }
>            }
>        }
>        return len1 - len2;
>    }
> 
> comparing this with Name.hashCode:
> 
>        public int hashCode() {
>            if (hashCode == -1) {
>                hashCode = name.toLowerCase(Locale.ROOT).hashCode();
>            }
>            return hashCode;
>        }
> 
> 
> ...is it possible that for some pair of keys, compareToCI would result in 0, but hashCode(s) would differ? For example, the uppercased keys would be the same, but the .toLowerCase(Locale.ROOT) not? Maybe not for LATIN1 keys, but what if one uses non-latin1 keys (StringUTF16.compareToCI is similar)?

Can this really happen? ASCIICaseInsensitiveComparator was asserting that 
string characters were ASCII, so this situation would have triggered an assert
with the old code, no?

-Chris.