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From "Venkatesh Prasad Ranganath (JIRA)" <j...@apache.org>
Subject [jira] Created: (LANG-345) Optimize HashCodeBuilder.append(Object)
Date Wed, 04 Jul 2007 19:23:04 GMT
Optimize HashCodeBuilder.append(Object)
---------------------------------------

                 Key: LANG-345
                 URL: https://issues.apache.org/jira/browse/LANG-345
             Project: Commons Lang
          Issue Type: Improvement
    Affects Versions: 2.3
            Reporter: Venkatesh Prasad Ranganath
            Priority: Minor
             Fix For: 2.3.1


In HashCodeBuilder.append(Object), java.lang.Class.isArray() is used to check if the input
argument is an array.  This check is expensive in comparison with an "instanceof" check. 
While a single instanceof check will not suffice, even the required 9 instance of checks prove
to be faster than this single check.  This is illustrated by the data from a profiling session.

CPU SAMPLES BEGIN (total = 71) Sat Jun 30 16:51:43 2007
rank   self  accum   count trace method
   1 45.07% 45.07%      32 300138 java.lang.Class.isArray
   2 14.08% 59.15%      10 300141 java.util.AbstractList.hashCode
   3 12.68% 71.83%       9 300142 java.util.AbstractList.hashCode
   4  4.23% 76.06%       3 300030 sun.nio.cs.UTF_8$Decoder.decodeArrayLoop   
   5  4.23% 80.28%       3 300144 java.util.AbstractList.hashCode
   6  2.82% 83.10%       2 300143 Test.run2
   7  2.82% 85.92%       2 300139 java.util.ArrayList.get
   8  1.41% 87.32%       1 300140 java.util.AbstractList.hashCode
   9  1.41% 88.73%       1 300145 java.util.AbstractList.hashCode
  10  1.41% 90.14%       1 300027 sun.nio.cs.UTF_8$Decoder.<init>
  11  1.41% 91.55%       1 300012 java.nio.DirectByteBuffer.<init>
  12  1.41% 92.96%       1 300089 sun.security.provider.Sun.<clinit>
  13  1.41% 94.37%       1 300132 sun.security.provider.Sun.<init>
  14  1.41% 95.77%       1 300071 java.lang.StringCoding.decode
  15  1.41% 97.18%       1 300031 sun.reflect.NativeConstructorAccessorImpl.newInstance  
  16  1.41% 98.59%       1 300048 java.net.URLClassLoader.defineClass
  17  1.41% 100.00%       1 300137
sun.net.www.ParseUtil.canonizeStringCPU SAMPLES END

The profiled program is given below.  While run1() uses HashCodeBuilder.append(Object), run2()
uses an optimized version of the same code.  While 45% of the time is spent in Class.isArray()
(hence, in run1()), only ~3% of the time is spent in run2().  So,  we can replace the body
of HashCodeBuilder.append(Object) with that from OptimizedHashCodeBuilder.append(Object) and
improve the performance by 15x.

import org.apache.commons.lang.builder.HashCodeBuilder;

public class Test {

  public static void main(String[] s) {
    java.util.ArrayList o = new java.util.ArrayList();
    o.add("Hello");
    o.add("World");
    run1(o);
    run2(o);
  }

  static void run1(Object o) {
    for (int i = 0; i < 10000; i++) {
      HashCodeBuilder h = new HashCodeBuilder();
      for (int k = 0; k < 100; k++) {
        h = h.append(o);
      }
    }
  }

  static void run2(Object o) {
    for (int i = 0; i < 10000; i++) {
      HashCodeBuilder h = new OptimizedHashCodeBuilder();
      for (int k = 0; k < 100; k++) {
        h = h.append(o);
      }
    }
  }
}

class OptimizedHashCodeBuilder extends HashCodeBuilder {
        public HashCodeBuilder append(final Object object) {
                if (object == null) {
                        super.append(object);

                } else {
                        // 'Switch' on type of array, to dispatch to the correct handler
                        // This handles multi dimensional arrays
                        if (object instanceof long[]) {
                                append((long[]) object);
                        } else if (object instanceof int[]) {
                                append((int[]) object);
                        } else if (object instanceof short[]) {
                                append((short[]) object);
                        } else if (object instanceof char[]) {
                                append((char[]) object);
                        } else if (object instanceof byte[]) {
                                append((byte[]) object);
                        } else if (object instanceof double[]) {
                                append((double[]) object);
                        } else if (object instanceof float[]) {
                                append((float[]) object);
                        } else if (object instanceof boolean[]) {
                                append((boolean[]) object);
                        } else if (object instanceof Object[]) {
                                // Not an array of primitives
                                append((Object[]) object);
                        } else {
                                // the simple case, not an array, just the element
                                append(object.hashCode());
                        }
                }
                return this;
        }
}


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