[9] RFR(S): 8048721: -XX:+PrintCompilation prints negative bci for non entrant OSR methods

[Vladimir Ivanov]

(widening audience to Runtime folks)

I don't think it's good to lose bci for OSR methods after nmethod 
invalidation.

Regarding current invalidation logic, I don't see that "_entry_bci = 
InvalidOSREntryBci" is required to invalidate OSR nmethods. Yes, 
interpreter does "_entry_bci != InvalidOSREntryBci" check before calling 
OSR nmethod, but _entry_bci update isn't properly synchronized between 
invalidating and querying threads (no locks or memory barriers involved).

So I have a question is it safe to remove "_entry_bci = InvalidOSREntryBci".

Both OSR nmethod lookup (InstanceKlass::lookup_osr_nmethod) and removal 
(InstanceKlass::remove_osr_nmethod) synchronize on OsrList_lock, so 
after removal OSR nmethod can't be looked up.

What bothers me is the following null check before removal:
void nmethod::invalidate_osr_method() {
   if (method() != NULL)
     method()->method_holder()->remove_osr_nmethod(this);

Under what conditions nmethod with _method == NULL can be invalidated? 
Or is it just defensive coding?

We set _method to NULL only for zombie nmethods (see 
nmethod::make_not_entrant_or_zombie) and they are already invalidated at 
that point.

Best regards,
Vladimir Ivanov

On 7/1/14 2:48 PM, Tobias Hartmann wrote:
> Hi,
>
> please review the following patch for JDK-8048721.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8048721
> Webrev: http://cr.openjdk.java.net/~thartmann/8048721/webrev.00/
>
> *Problem*
> The VM option -XX:+PrintCompilation prints a negative bytecode index for
> not entrant OSR nmethods. The problem is that in
> nmethod::make_not_entrant_or_zombie(..) the _entry_bci is invalidated
> (i.e. set to InvalidOSREntryBci == -2) by invalidate_osr_method(..) and
> log_state_change(..) is called afterwards, printing the invalidated entry.
>
> *Solution
> *Because reordering the methods in
> nmethod::make_not_entrant_or_zombie(..) is not easily possible due to
> thread safety, I changed the implementation log_state_change(..) and
> dependent methods to take the entry bci as parameter. The entry bci is
> saved prior to invalidation and used for printing afterwards.
>
> *Testing*
> JPRT
>
> Thanks,
> Tobias