RFR: 5043030 (reflect) unnecessary object creation in reflection (original) (raw)

David Holmes david.holmes at oracle.com
Mon Jun 2 03:07:23 UTC 2014

Hi Andrej,

Sorry for the delay getting back to you.

On 29/05/2014 10:24 PM, Andrej Golovnin wrote:

Hi David,

The valueOf calls may also allocate a new object so you can't just delete the JvmtiExport::postvmobjectalloc call. Unfortunately you can't tell whether a new object was allocated or not. It is only for the smaller primitive types that any kind of Object caching is mandated. It is only for the smaller values (-128 to +127) of the integer primitives types (plus boolean) that caching is mandated. Float.valueOf and Double.valueOf always create objects. You are right, that #valueOf call may allocate an object. But as far as I understand currently the JvmtiExport::postvmobjectalloc call is only needed, because today the native code itself allocates an object by calling javalangboxingobject::create(type, value, CHECKNULL);.

Right, sorry - I was misunderstanding the purpose of the post_vm_object_alloc call:

http://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#VMObjectAlloc

So from the perspective that you are diverting this back to Java code the hotspot changes look okay to me.

The more general question, for the core-libs folk, is whether changing everything to use valueOf is overkill (given the limits of the required caching mechanisms) or good to do from a consistency perspective. I'm slightly on the overkill side of things but not enough to reject things.

On the performance/benefit side, if I read things correctly you only see the 9GB of Boolean objects because you disable reflection-inflation - is that right? In that case, as Joel states, the gains are not really general, but on the other hand I don't see anything wrong with trying to improve the general efficiency here even if the greatest benefit comes from a "non-mainstream" usecase.

David

My code changes this behavior and delegates object allocation back to Java by calling

JavaCalls::callstatic(&boxedvalue, klasshandle, vmSymbols::valueOfname(), valueOfsignature, &args, THREAD); But maybe I misunderstood the implementation of JavaCalls. Best regards, Andrej Golovnin

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