using JVMTI to get a collection with all instances of a class?

[SainTiss]

Hi,

basically, I'm trying to find a way to fetch all instances of a certain
class in Java, i.e. something like an allInstances() operator on
java.lang.Class, but obviously that doesn't exist.
I stumbled upon JVMTI, which seems to be able to access instances of a class
on the heap, using this function:
IterateOverInstancesOfClass(jvmtiEnv* env,
jclass klass,
jvmtiHeapObjectFilter object_filter,
jvmtiHeapObjectCallback heap_object_callback,
void* user_data)

Now a few things are unclear:
- is it possible to actually "call" this function from within a java
program? Because it seems jvmti is typically used in programs which run
outside the VM and just "monitor" it, so actually the java program is
unaware.
So maybe the only thing possible is generate an event and make sure the
monitor reacts?
- Supposing the function can be invoked somehow, will it be able to return a
value, and more specifically a collection of these instances? Or will it
only be able to collect information of these instances?
- Is there a better way to accomplish what I want?

Thanks,

Hans

[robert.field]

Hi Hans,

JVM TI can be called from JNI code. So simply create a native method
which calls the JVM TI function.

Since the heap walking functions operate on tags not objects, if you
want the return objects you will need to tag the objects with the
callbacks (they could all get the same tag). Then retrieve the
objects with GetObjectsWithTags.

As to if this is the best approach, that depends on what you are
trying to do. What are you trying to do?
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