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.
-------------
Commit messages:
- Collections:addAll: instead of one-by-one add elements in bulk
Changes: https://git.openjdk.java.net/jdk/pull/1764/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1764&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8193031
Stats: 7 lines in 1 file changed: 1 ins; 4 del; 2 mod
Patch: https://git.openjdk.java.net/jdk/pull/1764.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/1764/head:pull/1764
PR: https://git.openjdk.java.net/jdk/pull/1764
