RFR: 8196340: (coll) Examine overriding inherited methods in ArrayList and ArrayList.SubList

[Martin Buchholz]

Yet another way to iterate over a collection.  Coming in via jsr166 soon.

Seeing CopyOnWriteArrayList beat ArrayList decisively suggests that
optimizing it is defintely worth doing.

And of course the numbers below contain more low-hanging fruit if anyone
still cares about the performance of LinkedList or Vector.

Have you considered adding public ranged methods on Arrays?  We currently
only have the "deranged" Arrays.hashCode(Object[])

--- IteratorMicroBenchmark.java 9 May 2018 17:43:01 -0000 1.44
+++ IteratorMicroBenchmark.java 11 May 2018 18:18:37 -0000
@@ -34,6 +34,7 @@
 import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
 import java.util.ArrayDeque;
+import java.util.Arrays;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -562,6 +563,12 @@
                     for (int i = 0; i < iterations; i++) {
                         sum[0] = 0;
                         x.replaceAll(sneakyAdder);
-                        check.sum(sum[0]);}}});
+                        check.sum(sum[0]);}}},
+            new Job(klazz + " hashCode") {
+                public void work() throws Throwable {
+                    int hashCode = Arrays.hashCode(x.toArray());
+                    for (int i = 0; i < iterations; i++) {
+                        if (x.hashCode() != hashCode)
+                            throw new AssertionError();}}});
     }
 }


C2:
Method                                Millis Ratio
ArrayList hashCode                        94 1.000
ArrayList$SubList hashCode                97 1.031
LinkedList hashCode                       92 0.974
AbstractList$SubList hashCode            111 1.172
Vector hashCode                           82 0.866
SynchronizedRandomAccessList hashCode     97 1.022
CopyOnWriteArrayList hashCode              8 0.091
COWSubList hashCode                        8 0.090

C1:
Method                                Millis Ratio
ArrayList hashCode                       112 1.000
ArrayList$SubList hashCode               118 1.060
LinkedList hashCode                      118 1.054
AbstractList$SubList hashCode            276 2.472
Vector hashCode                          126 1.132
SynchronizedRandomAccessList hashCode    293 2.620
CopyOnWriteArrayList hashCode             37 0.330
COWSubList hashCode                       36 0.325