Proxy.isProxyClass scalability

Mandy Chung mandy.chung at
Thu Apr 25 21:53:57 UTC 2013

Hi Peter,

This looks great.  I have imported your patch with slight modification 
in WeakCache:

I believe WeakCache.get(K, P) should throw NPE if key is null and I 
fixed that.  I changed refQueue to be of type ReferenceQueue<K> rather 
than ReferenceQueue<Object> since CacheValue no longer added to the ref 
queue.  In the expungeStaleEntries method, change CacheKey<?> to 
CacheKey<K>.  WeakCache.get(K, P) takes instance of K and P but 
subKeyFactory and valueFactory take superclasses of K and P - is that 
what you really want?  I have changed them to BiFunction<K,P,...>. I 
also fixed a few typos and that's all.

The performance improvement is significant and I want to push this 
version to jdk8/tl.  We can tune the memory usage in the future if that 
turns out to be an issue.  I don't have plan to backport to jdk7u-dev 
unless there are customers escalating this :)  This should be easy to 
convert without using BiFunction and Supplier and I will leave it as it 
is until there is a request to backport.

I keep Key2 class since jdk also creates a proxy of 2 interfaces and you 
have already implemented it.  If we think of a better way to replace the 
generation of the subkey in an optimized way, we could improve that in 
the future.  The first and second level maps maintained in the WeakCache 
have Object as the type for the key which I think we should look for a 
specific type (CacheKey and SubKey type).  To make the key of the 
first-level map to CacheKey would need to keep a separate cache for null 
key.  For the second-level map, the subkey type would need to be 
declared as a parameter type to WeakCache.  They are something that we 
should look at and clean up in the future if appropriate.  I think what 
you have is good work that shouldn't be delayed any further.

I'm running more tests.  If the above webrev looks fine with you, I'll 
push the changeset tomorrow.


On 4/25/13 8:40 AM, Peter Levart wrote:
> Hi Mandy,
> Here's another update that changes the sub-key back to 
> WeakReference<Class> based:
> On 04/25/2013 03:38 AM, Mandy Chung wrote:
>> I like this one too.  The mapping is straight forward and clean that 
>> avoids the fallback and post validation path. Let's proceed with this 
>> one.  It's good to optimize for the common case (1-interface). For 2 
>> or more interfaces, we can improve the memory usage in the future 
>> when it turns out to be an issue.  I'm fine with the zero-interface 
>> proxy which is the current implementation too.
> I made 3 straight-forward implementations of sub-keys:
> - Key1 - single interface
> - Key2 - two interfaces
> - KeyX - any number of interfaces
> The cache-structure size increment for each new cached proxy-class is 
> (32 bit OOPS):
> #of intfcs  original  patched
> ----------  --------  ------------
>          1       152  128(Key1)
>          2       152  168(Key2), 208(KeyX)
>          3       160  248(KeyX)
>          4       160  280(KeyX)
> you can decide if Key2 is worth having or not.
>>    The javadoc for the get(K,P) method - @throws RuntimeException and 
>> @throws Error are not needed here since any method being called in 
>> the implementation may throw unchecked exceptions.  There are a 
>> couple places that checks if (reverseMap != null) .... that check is 
>> not needed since it's always non-null.  But I'm fine if you keep it 
>> as it is - just wanted to mention it in case it was just leftover 
>> from the previous version.
> Removed the unneeded @throws and reverseMap != null checks (the later 
> was already removed in latest string-based webrev and I used that 
> version here).
>> I think we're very close of getting this pushed.
> Do you think this could also get backported to JDK7? The WeakCache 
> uses two interfaces from java.util.function. Should we make private 
> equivalents in this patch or do we leave that for the possible 
> back-porting effort. I should note that JDK7's ConcurrentHashMap is 
> not that space-efficient as proposed JDK8's, so space-usage would be 
> different on JDK7...
> Regards, Peter
>> thanks
>> Mandy

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