Review request: 8009174: add class load event tracing

[David Holmes]

On 1/03/2013 5:37 PM, Staffan Larsen wrote:
>
> On 1 mar 2013, at 07:57, David Holmes <David.Holmes at oracle.com> wrote:
>
>> Hi Calvin,
>>
>> So this adds the code that would allow for the event tracing but it doesn't actually add the code that will do the event tracing ???
>
> It does add the code that creates the event and pushes it into the event tracing framework. This is all that is required to add a new event to the event tracing.

Now that was weird. When I loaded the webrev the systemDictionary.cpp 
change stopped just after the post_class_load_event method. I didn't see 
the changes that used the post_class_load_event method.

So now that I can see them ... the event is being recorded prematurely:

  816       // If everything was OK (no exceptions, no null return value),
  817       // post a class load event.
  818       if (!HAS_PENDING_EXCEPTION && !k.is_null()) {
  819         // post class load event
  820         post_class_load_event(starttime, k, class_loader);
  821
  822         // class_loader is NOT the defining loader, do a little 
more bookkeeping.
  823         if (k->class_loader() != class_loader()) {

  824
  825           check_constraints(d_index, d_hash, k, class_loader, 
false, THREAD);
  826
  827           // Need to check for a PENDING_EXCEPTION again; 
check_constraints
  828           // can throw and doesn't use the CHECK macro.

The class isn't really loaded until it has passed the loader constraint 
check. And later the protection domain validation check could fail.

>> Second problem: you can't store raw oops into the event. Even if classloader oops were somehow non-moving, the loader may not exist at the time the event is examined.
>
> You can store raw oops into the event. We take care to make sure they are never referenced after the commit() is called.

Sorry I misread the code. You don't store the loader oop you store the 
klass() - so this just records the type of the Loader rather than 
identifying the actual instance. What do you do with these values - just 
treat them as addresses that you print? (Same question if you store oops 
- what can you do with an oop you can't reference?)

David

> /Staffan
>
>>
>> David
>>
>> On 1/03/2013 9:24 AM, Calvin Cheung wrote:
>>> This change is for adding the class load event tracing.
>>> The event will include the following fields:
>>> loaded class
>>> defining class loader
>>> initiating class loader
>>>
>>> webrev: http://cr.openjdk.java.net/~ccheung/8009174/webrev/
>>>
>>> thanks,
>>> Calvin
>