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From Abe White <awh...@bea.com>
Subject Re: svn commit: r506230 - in /incubator/openjpa/trunk: openjpa-kernel/src/main/java/org/apache/openjpa/ee/ openjpa-kernel/src/main/java/org/apache/openjpa/kernel/ openjpa-kernel/src/main/java/org/apache/openjpa/util/ openjpa-kernel/src/main/resources/org/a...
Date Mon, 12 Feb 2007 17:23:19 GMT

> ====================================================================== 
> ========
> --- incubator/openjpa/trunk/openjpa-kernel/src/main/java/org/apache/ 
> openjpa/ee/JNDIManagedRuntime.java (original)
> +++ incubator/openjpa/trunk/openjpa-kernel/src/main/java/org/apache/ 
> openjpa/ee/JNDIManagedRuntime.java Sun Feb 11 18:33:05 2007
> @@ -29,6 +29,7 @@
>      implements ManagedRuntime {
>
>      private String _tmLoc = "java:/TransactionManager";
> +    private static TransactionManager _tm;

Whoa, I didn't think you meant caching the TM statically.  That has  
to be backed out.  You can cache it in an instance variable, but not  
statically.  Nothing should prevent someone having two different  
BrokerFactories accessing two different TMs at two different JNDI  
locations.

BrokerImpl:
> +     * Cache from/to assignments to avoid Class.isAssignableFrom  
> overhead
> +     * @param from the target Class
> +     * @param to the Class to test
> +     * @return true if the "to" class could be assigned to "from"  
> class
> +     */
> +    private boolean isAssignable(Class from, Class to) {
> +      boolean isAssignable;
> +      ConcurrentReferenceHashMap assignableTo =
> +          (ConcurrentReferenceHashMap) _assignableTypes.get(from);
> +
> +      if (assignableTo != null) { // "to" cache exists...
> +          isAssignable = (assignableTo.get(to) != null);
> +          if (!isAssignable) { // not in the map yet...
> +              isAssignable = from.isAssignableFrom(to);
> +              if (isAssignable) {
> +                  assignableTo.put(to, new Object());
> +              }
> +          }
> +      } else { // no "to" cache yet...
> +          isAssignable = from.isAssignableFrom(to);
> +          if (isAssignable) {
> +              assignableTo = new ConcurrentReferenceHashMap(
> +                      ReferenceMap.HARD, ReferenceMap.WEAK);
> +              _assignableTypes.put(from, assignableTo);
> +              assignableTo.put(to, new Object());
> +          }
> +      }
> +      return isAssignable;
> +    }

This code could be simplified a lot.  Also, I don't understand what  
you're trying to do from a memory management perspective.  For the  
_assignableTypes member you've got the Class keys using hard refs and  
the Map values using weak refs.  No outside code references the Map  
values, so all entries should be eligible for GC pretty much  
immediately.  The way reference hash maps work prevents them from  
expunging stale entries except on mutators, but still... every time a  
new entry is added, all the old entries should be getting GC'd and  
removed.  Same for the individual Map values, which again map a hard  
class ref to an unreferenced object value with a weak ref.  Basically  
the whole map-of-maps system should never contain more than one entry  
total after a GC run and a mutation.

I'd really like to see you run your tests under a different JVM,  
because it seems to me like (a) this shouldn't be necessary in the  
first place, and (b) if this is working, it's again only because of  
some JVM particulars or GC timing particulars or testing particulars  
(I've seen profilers skew results in random ways like this) or even a  
bug in ConcurrentReferenceHashMap.

The same goes for all the repeat logic in FetchConfigurationImpl.   
And if we keep this code or some variant of it, I strongly suggest  
moving it to a common place like ImplHelper.

> +    /**
> +     * Generate the hashcode for this Id.  Cache the type's  
> generated hashcode
> +     * so that it doesn't have to be generated each time.
> +     */
>      public int hashCode() {
>          if (_typeHash == 0) {
> -            Class base = type;
> -            while (base.getSuperclass() != null
> -                && base.getSuperclass() != Object.class)
> -                base = base.getSuperclass();
> -            _typeHash = base.hashCode();
> +            Integer typeHashInt = (Integer) _typeCache.get(type);
> +            if (typeHashInt == null) {
> +                Class base = type;
> +                Class superclass = base.getSuperclass();
> +                while (superclass != null && superclass !=  
> Object.class) {
> +                    base = base.getSuperclass();
> +                    superclass = base.getSuperclass();
> +                }
> +                _typeHash = base.hashCode();
> +                _typeCache.put(type, new Integer(_typeHash));
> +            } else {
> +                _typeHash = typeHashInt.intValue();
> +            }
>          }
>          return _typeHash ^ idHash();
>      }

Once again, you're mapping a hard Class ref to a value with no  
outside references held in a weak ref.  Once again that means the  
entry should be immediately eligible for GC, and therefore should be  
removed on the next mutation of the cache, subject to GC timing.  And  
again I'd like to know what your JVM is doing to make Class.hashCode  
take an appreciable amount of time.  Aren't Class instances supposed  
to be singletons?  What if we just used System.identityHashCode(cls)?

> Modified: incubator/openjpa/trunk/openjpa-lib/src/main/java/org/ 
> apache/openjpa/lib/conf/ObjectValue.java
> URL: http://svn.apache.org/viewvc/incubator/openjpa/trunk/openjpa- 
> lib/src/main/java/org/apache/openjpa/lib/conf/ObjectValue.java? 
> view=diff&rev=506230&r1=506229&r2=506230
> ====================================================================== 
> ========
> --- incubator/openjpa/trunk/openjpa-lib/src/main/java/org/apache/ 
> openjpa/lib/conf/ObjectValue.java (original)
> +++ incubator/openjpa/trunk/openjpa-lib/src/main/java/org/apache/ 
> openjpa/lib/conf/ObjectValue.java Sun Feb 11 18:33:05 2007
> @@ -17,6 +17,8 @@
>
>  import org.apache.commons.lang.ObjectUtils;
>  import org.apache.openjpa.lib.util.Localizer;
> +import org.apache.openjpa.lib.util.ReferenceMap;
> +import  
> org.apache.openjpa.lib.util.concurrent.ConcurrentReferenceHashMap;
>
>  /**
>   * An object {@link Value}.
> @@ -28,6 +30,10 @@
>      private static final Localizer _loc = Localizer.forPackage
>          (ObjectValue.class);
>
> +    // cache the types' classloader
> +    private static ConcurrentReferenceHashMap _classloaderCache =
> +        new ConcurrentReferenceHashMap(ReferenceMap.HARD,  
> ReferenceMap.WEAK);

This maps a hard Class ref to a weak ClassLoader ref.  Given that a  
Class references its ClassLoader (or is supposed to -- again I wonder  
what the hell the JVM you're using is doing where  
Class.getClassLoader is taking a long time), no entries will ever  
expire from this map.

Have you tried running your benchmarks without all the caching of  
assignables and classloaders and hashcodes (all Class methods, btw)  
and just the other improvements?  Or with any other JVM? 
  
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