Hello! Please review and sponsor the following patch: https://bugs.openjdk.java.net/browse/JDK-8155600 http://cr.openjdk.java.net/~tvaleev/webrev/8155600/r1/
It appears that custom implementation of Arrays.asList().iterator() is noticeably more performant than the AbstractList implementation used currently. Here's JMH test which illustrates this: http://cr.openjdk.java.net/~tvaleev/webrev/8155600/jmh/ @Benchmark public int sumList() { return sum(list); } @Benchmark public int sumArray() { return sum(Arrays.asList(arr)); } public static int sum(Iterable<Integer> data) { int sum = 0; for (int item : data) sum+=item; return sum; } Here's summary result on my Intel x64 machine: JDK 9ea+115: Benchmark (limit) Mode Cnt Score Error Units ArrayTest.sumArray 0 avgt 50 6,371 ± 0,009 ns/op ArrayTest.sumArray 1 avgt 50 8,020 ± 0,100 ns/op ArrayTest.sumArray 10 avgt 50 14,424 ± 0,060 ns/op ArrayTest.sumArray 100 avgt 50 88,684 ± 3,261 ns/op ArrayTest.sumArray 1000 avgt 50 677,048 ± 1,050 ns/op ArrayTest.sumArray 10000 avgt 50 8038,224 ± 59,678 ns/op ArrayTest.sumList 0 avgt 50 3,395 ± 0,003 ns/op ArrayTest.sumList 1 avgt 50 5,613 ± 0,061 ns/op ArrayTest.sumList 10 avgt 50 13,448 ± 0,076 ns/op ArrayTest.sumList 100 avgt 50 97,242 ± 0,105 ns/op ArrayTest.sumList 1000 avgt 50 664,342 ± 0,704 ns/op ArrayTest.sumList 10000 avgt 50 7971,230 ± 61,344 ns/op JDK 9ea+115 patched: Benchmark (limit) Mode Cnt Score Error Units ArrayTest.sumArray 0 avgt 50 2,932 ± 0,011 ns/op ArrayTest.sumArray 1 avgt 50 5,000 ± 0,062 ns/op ArrayTest.sumArray 10 avgt 50 9,421 ± 0,219 ns/op ArrayTest.sumArray 100 avgt 50 43,848 ± 0,187 ns/op ArrayTest.sumArray 1000 avgt 50 383,619 ± 1,019 ns/op ArrayTest.sumArray 10000 avgt 50 6860,087 ± 13,022 ns/op ArrayTest.sumList 0 avgt 50 3,400 ± 0,008 ns/op ArrayTest.sumList 1 avgt 50 6,142 ± 0,047 ns/op ArrayTest.sumList 10 avgt 50 12,488 ± 0,084 ns/op ArrayTest.sumList 100 avgt 50 83,029 ± 0,078 ns/op ArrayTest.sumList 1000 avgt 50 605,651 ± 0,992 ns/op ArrayTest.sumList 10000 avgt 50 7649,681 ± 16,355 ns/op AbstractList.iterator() makes unnecessary bookkeeping like modCount tracking which reduces the performance. Also it seems that having implicit this$0 field in AbstractList.iterator() makes impossible to avoid allocation of short-lived Arrays.ArrayList object in sumArray() test. Launching JMH -prof gc confirms that non-patched sumArray() test allocates 24 bytes per invocation while patched sumArray() does not allocate anything. What do you think? Is it reasonable change? Should I check some tests or add new ones for this optimization? With best regards, Tagir Valeev.
