RFR (M) 8046246: the constantPoolCacheOopDesc::adjust_method_entries() used in RedefineClasses does not scale

[serguei.spitsyn at oracle.com]

Please, review the fix for:
   https://bugs.openjdk.java.net/browse/JDK-8046246


Open hotspot webrevs:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/hotspot/8046246-JVMTI-redefscale.1/

Open jdk (new unit test) webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/jdk/8046246-JVMTI-manymethods.1/


Summary:

    This performance/scalability issue in class redefinition was 
reported by HP and the Enterprise Manager team.
    The following variants of the adjust_method_entries() functions do 
not scale:
      ConstantPoolCache::adjust_method_entries()
      klassVtable::adjust_method_entries()
      klassItable::adjust_method_entries()
      InstanceKlass::adjust_default_methods()

    The ConstantPoolCache::adjust_method_entries() is the most important.

    The approach is to use the holder->method_with_idnum() like this:
      Method* new_method = 
holder->method_with_idnum(old_method->orig_method_idnum());
      if (old_method != new_method) {
          <replace old_method with new_method>
      }

      New algorithm has effectiveness O(M) instead of original O(M^2),
      where M is count of methods in the class.
      The new test (see webrev above) was used to mesure CPU time 
consumed by the
      ConstantPoolCache::adjust_method_entries() in both original and 
new approach.

      The performance numbers are:

---------------------------------------------------------------------------------------
      Methods: ------ 1,000 --------------- 10,000 ----------------- 20,000
---------------------------------------------------------------------------------------
      Orig:         600,000 nsec (1x)   60,500,000 nsec (~100x) 
243,000,000 nsec (~400x)
      New:           16,000 nsec (1x)      178,000 nsec (~10x) 355,000 
nsec  (~20x)
---------------------------------------------------------------------------------------



Testing:
   In progress: VM SQE RedefineClasses tests, JTREG 
java/lang/instrument, com/sun/jdi tests


Thanks,
Serguei