[9, 8u40] RFR (M): 8057020: LambdaForm caches should support eviction

[Vladimir Ivanov]

Thanks, Paul!
Updated webrev in place.

> On Dec 1, 2014, at 5:58 PM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
>
>> http://cr.openjdk.java.net/~vlivanov/8057020/webrev.00/
>> https://bugs.openjdk.java.net/browse/JDK-8057020
>>
>
> That LambdaFormEditor.putInCache method just got more gnarly :-)
>
> Generally looks good.
>
> In src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java
>
>   366                     lambdaForm.transformCache = c = ta;
>
> Do you need to set "c"? It's a local variable and by this point the method should return rather than loop.
I did it mostly as a cleanup. Now I think that it doesn't help much. 
Removed (+ similar change in another place).

> In test/java/lang/invoke/LFCaching/LambdaFormTestCase.java
>
>    55     private static final List<GarbageCollectorMXBean> gcInfo;
>    56
>    57     private static long gcCount() {
>    58         return gcInfo.stream()
>    59                 .map(GarbageCollectorMXBean::getCollectionCount)
>    60                 .reduce(0L, Long::sum);
>    61     }
>
> You can do:
>
>    gcInfo.stream().mapToLong(GarbageCollectorMXBean::getCollectionCount).sum();
Good point. Updated.

Best regards,
Vladimir Ivanov

>
> Paul.
>
>> There are 2 major LambdaForm caches: LambdaFormEditor-based and MethodTypeForm. The former is per-LambdaForm and the latter is per method type erased to basic types. The problem is that these caches don't support eviction, so they can hold LambdaForms forever.
>>
>> Usually, it's not a problem since an application has very limited number of unique erased method types (e.g. on Octane/Nashorn it varies 1,5-3k shapes).
>>
>> The fix is to use SoftReferences to keep LambdaForms alive as long as possible, but avoid throwing OOME until the caches are evicted. I experimented with WeakReferences, but it doesn't hold LambdaForms for long enough: LambdaForm cache hit rate degrades significantly and it negatively affects application startup and warmup, since every instantiated LambdaForm is precompiled to bytecode before usage.
>>
>> Testing: jdk/java/lang/invoke/LFCache in stress mode + jck (api/java_lang/invoke), jdk/java/lang/invoke, jdk/java/util/streams, octane
>>
>> Thanks!
>>
>> Best regards,
>> Vladimir Ivanov
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