JVM/TI code review request (XS and M) (7182152)

Daniel D. Daugherty daniel.daugherty at oracle.com
Mon Feb 4 08:40:16 PST 2013


Thanks for the reviews!  Replies embedded below.

On 2/4/13 8:19 AM, Karen Kinnear wrote:
> Dan,
> All 3 versions of the code looks good. Thank you for enabling the printing for product since
> this type of problem is so hard to duplicate.

You're welcome.

> A small note, I think it would have been easier for the internal code logic
> for the CPCE::check_no_old_or_obsolete_entries to reverse the true/false,
> but no need to change.

The original code added by Robert on 2006.04.21 used "check_no_old_entries"
so I followed his lead in my rename.

> I would appreciate the comment from
> is_interesting_method_entry copied to check_no_old_or_obsolete_entries
> about virtual and final that f2 contains a method ptr instead of a vtable index.

So this comment here on line 498:

  497   if (is_vfinal()) {
  498     // virtual and final so _f2 contains method ptr instead of 
vtable index
  499     m = (methodOop)_f2;

Copied to this new block here:

  475   if (is_vfinal()) {
  476     methodOop m = (methodOop)_f2;

between line 475 and 476 (for the HSX23.6 version). Between line 580
and 581 in the HSX-24 version and between line 465 and 466 in the
HSX-25 version.

I'll make that change.

> In the jdk8 version in cpCache.cpp you've added the is_valid checks for metadata.

The is_valid() check may go away since the field it is using adds to
memory footprint. Stay tuned.

> For a future cleanup, do we need f2_as_vfinal_method and is_interesting_method_entry
> to do that as well?

This line in the HSX-25 version:

   466     Metadata* f2 = (Metadata*)_f2;

should probably have used f2_as_vfinal_method(). I'll have to check
with Coleen to find out if there is a reason why it doesn't; there
may be a good reason.

I noticed that there is quite a bit of "type cleanup" in the HSX-24
version of is_interesting_method_entry(), e.g.:

In HSX23.6:

  497   if (is_vfinal()) {
  498     // virtual and final so _f2 contains method ptr instead of 
vtable index
  499     m = (methodOop)_f2;
  500   } else if ((oop)_f1 == NULL) {
  501     // NULL _f1 means this is a virtual entry so also not interesting
  502     return false;

In HSX24:

  602   if (is_vfinal()) {
  603     // virtual and final so _f2 contains method ptr instead of 
vtable index
  604     m = f2_as_vfinal_method();
  605   } else if (is_f1_null()) {
  606     // NULL _f1 means this is a virtual entry so also not interesting
  607     return false;

check_no_old_or_obsolete_entries() could definitely benefit from
the better code in is_interesting_method_entry(). In particular,
this block in is_interesting_method_entry():

  491   if (!is_method_entry()) {
  492     // not a method entry so not interesting by default
  493     return false;
  494   }

is present in the HSX-23.6, HSX-24, and HSX-25 versions of
is_interesting_method_entry(), but is not used by the original
check_no_old_entries() or any of the new check_no_old_or_obsolete_entries().
I'll put that info in the new bug to track the future work.

> Is redefineclasses supported in the MinimalVM?

I don't know the answer to that. I have not been tracking the
MinimalVM work. I'll investigate and get back to you.

Again, thanks for the reviews.


> thanks,
> Karen
> On Feb 1, 2013, at 2:55 PM, Daniel D. Daugherty wrote:
>> Greetings,
>> I have a fix for the following JVM/TI bug:
>>     7182152 Instrumentation hot swap test incorrect monitor count
>>     http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7182152
>>     https://jbs.oracle.com/bugs/browse/JDK-7182152
>> The fix for the bug in the product code is one line:
>> src/share/vm/oops/klassVtable.cpp:
>> @@ -992,18 +1020,50 @@
>>            // RC_TRACE macro has an embedded ResourceMark
>>            RC_TRACE(0x00200000, ("itable method update: %s(%s)",
>>              new_method->name()->as_C_string(),
>>              new_method->signature()->as_C_string()));
>>          }
>> -        break;
>> +        // cannot 'break' here; see for-loop comment above.
>>        }
>>        ime++;
>>      }
>>    }
>> }
>> and is applicable to JDK7u10/HSX-23.6 and JDK7u14/HSX-24. Coleen
>> already fixed the bug as part of the Perm Gen Removal (PGR) project
>> in HSX-25. Yes, we found a 1-line bug fix buried in the monster PGR
>> changeset. Many thanks to Coleen for her help in this bug hunt!
>> The rest of the code in the webrevs are:
>> - additional JVM/TI tracing code backported from Coleen's PGR changeset
>> - additional JVM/TI tracing code added by me and forward ported to HSX-25
>> - a new -XX:TraceRedefineClasses=16384 flag value for finding these
>>   elusive old or obsolete methods
>> - exposure of some printing code to the PRODUCT build so that the new
>>   tracing is available in a PRODUCT build
>> You might be wondering why the new tracing code is exposed in a PRODUCT
>> build. Well, it appears that more and more PRODUCT bits deployments are
>> using JVM/TI RedefineClasses() and/or RetransformClasses() at run-time
>> to instrument their systems. This bug (7182152) was only intermittently
>> reproducible in the WLS environment in which it occurred so I made the
>> tracing available in a PRODUCT build to assist in the hunt.
>> Raj from the WLS team has also verified that the HSX-23.6 version of
>> fix resolves the issue in his environment. Thanks Raj!
>> Here are the URLs for the three webrevs:
>> http://cr.openjdk.java.net/~dcubed/7182152-webrev/0-hsx23.6/
>> http://cr.openjdk.java.net/~dcubed/7182152-webrev/0-hsx24/
>> http://cr.openjdk.java.net/~dcubed/7182152-webrev/0-hsx25/
>> I have run the following test suites from the JPDA stack on the
>> JDK7u10/HSX-23.6 version of the fix with -XX:TraceRedefineClasses=16384
>> specified:
>>     sdk-jdi
>>     sdk-jdi_closed
>>     sdk-jli
>>     vm-heapdump
>>     vm-hprof
>>     vm-jdb
>>     vm-jdi
>>     vm-jdwp
>>     vm-jvmti
>>     vm-sajdi
>> The tested configs are:
>>     {Solaris-X86, WinXP}
>>       X {Client VM, Server VM}
>>       X {-Xmixed, -Xcomp}
>>       X {product, fastdebug}
>> With the 1-liner fix in place, the new tracing code does not find any
>> instances of this failure mode in any of the above test suites. Without
>> the the 1-liner fix in place, the new tracing code finds one instance
>> of this failure mode in the above test suites:
>>     test/java/lang/instrument/IsModifiableClassAgent.java
>> There are two new tests that will be pushed to the JDK repos using
>> a different bug ID (not yet filed):
>>     test/com/sun/jdi/RedefineAbstractClass.sh
>> test/java/lang/instrument/RedefineSubclassWithTwoInterfaces.sh
>> There will be a separate review request for the new tests.
>> I'm currently running the JPDA stack of tests on the JDK7u14/HSX-24
>> and JDK8-B75/HSX-25 versions of the fix. That testing will likely
>> take all weekend to complete.
>> Thanks, in advance, for any comments and/or suggestions.
>> Dan

More information about the hotspot-runtime-dev mailing list