RFR (S) 8148936: Adapt UUID.toString() to Compact Strings

[Ivan Gerasimov]

Looks even better, thanks!

Sincerely yours,
Ivan

On 04.02.2016 14:54, Aleksey Shipilev wrote:
> Sure, here's a new webrev:
>    http://cr.openjdk.java.net/~shade/8148936/webrev.02/
>
> Cheers,
> -Aleksey
>
> On 02/04/2016 02:34 PM, Ivan Gerasimov wrote:
>> Hi Aleksey!
>>
>> Looks good to me!
>>
>> Two minorish comments
>>
>> 1)
>> 431             formatUnsignedLong0(lsb >> 48, 4, buf, 19, 4);
>> I would suggest using unsigned shift >>> here just to avoid thinking
>> about whether the sign matters or not.
>> Not a big deal, of course.
>>
>> 2)
>> Do you want to add the bug id 8148936 to the @bug list in the regression
>> test?
>>
>> Sincerely yours,
>> Ivan
>>
>>
>> On 03.02.2016 21:25, Aleksey Shipilev wrote:
>>> Hi,
>>>
>>> JDK-8006627 did the JavaLangAccess hack to improve UUID.toString()
>>> performance:
>>>
>>>       public String toString() {
>>>           char[] chars = new char[36];
>>>           jla.formatUnsignedLong(mostSigBits >> 32, 4, chars, 0, 8);
>>>           chars[8] = '-';
>>>           jla.formatUnsignedLong(mostSigBits >> 16, 4, chars, 9, 4);
>>>           chars[13] = '-';
>>>           jla.formatUnsignedLong(mostSigBits, 4, chars, 14, 4);
>>>           chars[18] = '-';
>>>           jla.formatUnsignedLong(leastSigBits >> 48, 4, chars, 19, 4);
>>>           chars[23] = '-';
>>>           jla.formatUnsignedLong(leastSigBits, 4, chars, 24, 12);
>>>           return jla.newStringUnsafe(chars);
>>>       }
>>>
>>> This is a good performance improvement, but it clashes with Compact
>>> Strings which now have to re-compress the resulting char[] array into
>>> byte[]. And we know that UUID would always produce Latin1 String.
>>>
>>> In fact, the entire JavaLangAccess.newStringUnsafe is now not doing what
>>> power users would expect: it *does* allocate now! So, we need to phase
>>> out that internal gateway to avoid confusion. UUID is one of these users
>>> (StringJoiner is another).
>>>
>>> This is the proposed fix:
>>>     http://cr.openjdk.java.net/~shade/8148936/webrev.01/
>>>
>>> My attempts in exposing the entire String coder business to UUID proved
>>> to be rather ugly, so I opted to just all into a single method, and let
>>> java/lang internals to sort this out.
>>>
>>> The patch does restore the post-Compact Strings performance, and even
>>> improves it further. See:
>>>     http://cr.openjdk.java.net/~shade/8148936/notes.txt
>>>
>>> Cheers,
>>> -Aleksey
>>>
>>>
>