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

[Paul Sandoz]

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.


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();

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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