request for review (XS), 6458402: 3 jvmti tests fail with CMS and +ExplicitGCInvokesConcurrent

[David Holmes]

Keith McGuigan said the following on 12/03/10 23:19:
> On Dec 3, 2010, at 3:30 AM, Igor Veresov wrote:
> 
>> You're calling notify_gc_end() while holding the FullGCCount_lock. Is 
>> that ok? Would it be more prudent to divert control to the user 
>> without holding it?
> 
> The notify_gc_end() call does not divert control to the user -- it 
> contains only the code that will trigger a dtrace event (which is a 
> no-op as far as the VM is concerned; the OS may notice it though).
> 
> That said, I think it would be a good idea to release the lock before 
> calling it and I'll change the code to do that.  That way if someone 
> adds code to the notify_gc_end() method in the future there won't be any 
> surprises.

But if you release the lock before firing the probe the two events can 
become distant in time and someone else can see a second "start" probe 
fire before they've seen the previous "end" probe fire. That makes it 
harder to use the probes to analyse what is happening.

David