RFR: 8196869: Optimize Locale creation

[Peter Levart]

Hi Claes,

I studied the code briefly and understand why BaseLocale.Key now has to 
hold a SoftReference to a BaseLocale object when the same object is also 
part of CacheEntry which is also a SoftReference. But I don't see a 
reason why pre-patch BaseLocale.Key had to hold SoftReference(s) to 
individual String attributes. Couldn't it simply hold strong references 
to individual String attributes instead? The 
LocaleObjectCache.cleanStaleEntryies() would remove cleared 
CacheEntry(s) together with corresponding Key(s) in that case too. So 
one SoftReference less, do you agree?

I don't know if it is important for LocaleObjectCache.get() to always 
return a canonicalized instance per key so that this always holds:

     (cache.get(k1) == cache.get(k2)) == k1.equals(k2)

If it is important, then I noticed a pre-existing race that violates 
above invariant:

   67             CacheEntry<K, V> newEntry = new CacheEntry<>(key, 
newVal, queue);
   68
   69             entry = map.putIfAbsent(key, newEntry);
   70             if (entry == null) {
   71                 value = newVal;
   72             } else {
   73                 value = entry.get();
   74                 if (value == null) {
   75                     map.put(key, newEntry);
   76                     value = newVal;
   77                 }
   78             }

...which can simply be fixed:

             CacheEntry<K, V> newEntry = new CacheEntry<>(key, newVal, 
queue);

             while (true) {
                 entry = map.putIfAbsent(key, newEntry);
                 if (entry == null) {
                     value = newVal;
                     break;
                 } else {
                     value = entry.get();
                     if (value == null) {
                         if (map.replace(key, entry, newEntry)) {
                             value = newVal;
                             break;
                         }
                     }
                 }
             }


Regards, Peter


On 02/07/2018 11:26 AM, Claes Redestad wrote:
> Hi Paul,
>
>
> On 2018-02-06 20:55, Paul Sandoz wrote:
>> Quick observation:
>>
>>   261         private BaseLocale getBaseLocale() {
>>   262             return (holder == null) ? holderRef.get() : holder;
>>   263         }
>>
>> This method can return null if the soft ref has been cleared.
>>
>>
>> But you don’t check in equals:
>>
>>   270             if (obj instanceof Key && this.hash == 
>> ((Key)obj).hash) {
>>   271                 BaseLocale other = ((Key) obj).getBaseLocale();
>>   272                 BaseLocale locale = this.getBaseLocale();
>>   273                 if 
>> (LocaleUtils.caseIgnoreMatch(other.getLanguage(), locale.getLanguage())
>
> good eye!
>
> It seems this wasn't caught by the existing regression tests since 
> none of them
> recreate Locales in that are likely to have been reclaimed, but still 
> likely to still
> be in the CHM (it's a race of sorts since they'll be removed when the 
> ReferenceQueue
> processing happen).
>
> I added a regression test with the smallest and quickest reproducer I 
> could come up
> with that provokes a NPE if we don't check null along with the fix to 
> Key#equals:
>
> http://cr.openjdk.java.net/~redestad/8196869/jdk.01/
>
> For the normalize(Key) case we can deduce that a !normalized Key will 
> always have
> a strongly referenced BaseLocale and thus not need to deal with 
> getBaseLocale()
> returning null. I clarified this in the code and added an assert (that 
> would be triggered
> by the added test if it wasn't true).
>
> Thanks!
>
> /Claes