On Mon, 14 Dec 2020 12:13:23 GMT, Сергей Цыпанов <github.com+10835776+stsypa...@openjdk.org> wrote:
> Hello, I feel like this was previously discussed in > https://mail.openjdk.java.net/pipermail/core-libs-dev/ but since I cannot > find original mail I post this here. > > Currently `Collections.addAll()` is implemented and documented as: > /** > * ... > * The behavior of this convenience method is identical to that of > * {@code c.addAll(Arrays.asList(elements))}, but this method is likely > * to run significantly faster under most implementations. > */ > @SafeVarargs > public static <T> boolean addAll(Collection<? super T> c, T... elements) { > boolean result = false; > for (T element : elements) > result |= c.add(element); > return result; > } > > But it practice the notation `this method is likely to run significantly > faster under most implementations` is completely wrong. When I take this > [benchmark](https://github.com/stsypanov/benchmarks/blob/master/benchmark-runners/src/main/java/com/luxoft/logeek/benchmark/collection/CollectionsAddAllVsAddAllBenchmark.java) > and run it on JDK 14 I get the following results: > (collection) (size) > Score Error Units > addAll ArrayList 10 > 37.9 ± 1.9 ns/op > addAll ArrayList 100 > 83.8 ± 3.4 ns/op > addAll ArrayList 1000 > 678.2 ± 23.0 ns/op > collectionsAddAll ArrayList 10 > 50.9 ± 1.1 ns/op > collectionsAddAll ArrayList 100 > 751.4 ± 47.4 ns/op > collectionsAddAll ArrayList 1000 > 8839.8 ± 710.7 ns/op > > addAll HashSet 10 > 128.4 ± 5.9 ns/op > addAll HashSet 100 > 1864.2 ± 102.4 ns/op > addAll HashSet 1000 > 16615.5 ± 1202.6 ns/op > collectionsAddAll HashSet 10 > 172.8 ± 6.0 ns/op > collectionsAddAll HashSet 100 > 2355.8 ± 195.4 ns/op > collectionsAddAll HashSet 1000 > 20364.7 ± 1164.0 ns/op > > addAll ArrayDeque 10 > 54.0 ± 0.4 ns/op > addAll ArrayDeque 100 > 319.7 ± 2.5 ns/op > addAll ArrayDeque 1000 > 3176.9 ± 22.2 ns/op > collectionsAddAll ArrayDeque 10 > 66.5 ± 1.4 ns/op > collectionsAddAll ArrayDeque 100 > 808.1 ± 55.9 ns/op > collectionsAddAll ArrayDeque 1000 > 5639.6 ± 240.9 ns/op > > addAll CopyOnWriteArrayList 10 > 18.0 ± 0.7 ns/op > addAll CopyOnWriteArrayList 100 > 39.4 ± 1.7 ns/op > addAll CopyOnWriteArrayList 1000 > 371.1 ± 17.0 ns/op > collectionsAddAll CopyOnWriteArrayList 10 > 251.9 ± 18.4 ns/op > collectionsAddAll CopyOnWriteArrayList 100 > 3405.9 ± 304.8 ns/op > collectionsAddAll CopyOnWriteArrayList 1000 > 247496.8 ± 23502.3 ns/op > > addAll ConcurrentLinkedDeque 10 > 81.4 ± 2.8 ns/op > addAll ConcurrentLinkedDeque 100 > 609.1 ± 26.4 ns/op > addAll ConcurrentLinkedDeque 1000 > 4494.5 ± 219.3 ns/op > collectionsAddAll ConcurrentLinkedDeque 10 > 189.8 ± 2.5 ns/op > collectionsAddAll ConcurrentLinkedDeque 100 > 1660.0 ± 62.0 ns/op > collectionsAddAll ConcurrentLinkedDeque 1000 > 17649.2 ± 300.9 ns/op > > addAll:·gc.alloc.rate.norm ArrayList 10 > 160.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm ArrayList 100 > 880.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm ArrayList 1000 > 8080.3 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ArrayList 10 > 80.0 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ArrayList 100 > 1400.2 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ArrayList 1000 > 15025.6 ± 0.1 B/op > > addAll:·gc.alloc.rate.norm HashSet 10 > 464.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm HashSet 100 > 5328.5 ± 0.0 B/op > addAll:·gc.alloc.rate.norm HashSet 1000 > 48516.7 ± 0.1 B/op > collectionsAddAll:·gc.alloc.rate.norm HashSet 10 > 464.0 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm HashSet 100 > 5328.5 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm HashSet 1000 > 48516.6 ± 0.1 B/op > > addAll:·gc.alloc.rate.norm ArrayDeque 10 > 112.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm ArrayDeque 100 > 560.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm ArrayDeque 1000 > 4160.5 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ArrayDeque 10 > 112.0 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ArrayDeque 100 > 1048.1 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ArrayDeque 1000 > 14929.4 ± 0.0 B/op > > addAll:·gc.alloc.rate.norm CopyOnWriteArrayList 10 > 88.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm CopyOnWriteArrayList 100 > 448.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm CopyOnWriteArrayList 1000 > 4048.1 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm CopyOnWriteArrayList 10 > 456.0 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm CopyOnWriteArrayList 100 > 22057.2 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm CopyOnWriteArrayList 1000 > 2020150.3 ± 7.3 B/op > > addAll:·gc.alloc.rate.norm ConcurrentLinkedDeque 10 > 312.0 ± 0.0 B/op > addAll:·gc.alloc.rate.norm ConcurrentLinkedDeque 100 > 2472.1 ± 0.0 B/op > addAll:·gc.alloc.rate.norm ConcurrentLinkedDeque 1000 > 24073.7 ± 0.1 B/op > collectionsAddAll:·gc.alloc.rate.norm ConcurrentLinkedDeque 10 > 288.0 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ConcurrentLinkedDeque 100 > 2448.3 ± 0.0 B/op > collectionsAddAll:·gc.alloc.rate.norm ConcurrentLinkedDeque 1000 > 24051.4 ± 0.3 B/op > There's never a case when `Collections.addAll` is fater - on the contrary > `c.addAll(Arrays.asList())` always wins. Pay attention especially to dramatic > difference for array-based collection. > > So I propose to reimplement the method by simply delegating to > `Arrays.asList` because the spec declares identical behaviour and to remove > perfomance notation from JavaDoc. Looks like I've found the original ticket: https://bugs.openjdk.java.net/browse/JDK-8193031 ------------- PR: https://git.openjdk.java.net/jdk/pull/1764
