CopyOnWriteArrayList implements an efficient List::replaceAll so you could do
something like:
====
public static void main(String[] args) {
List<String> cowl = new CopyOnWriteArrayList<>(new
String[]{"1","2","3"});
List<String> copy = Arrays.asList(cowl.toArray(new String[0]));
Collections.shuffle(copy);
Iterator<String> it = copy.iterator();
try {
cowl.replaceAll(e -> it.next());
} catch (NoSuchElementException nsee) {
throw new ConcurrentModificationException();
}
if (it.hasNext()) {
throw new ConcurrentModificationException();
}
System.out.println(cowl);
}
====
Some of the non-random access branches in Collections.java could be updated to
use List::replaceAll over ListIterator next/set. Once Collections.java was
using List::replaceAll you could then just wrap CopyOnWriteArrayList in a
non-random access list.
Jason
________________________________________
From: core-libs-dev <core-libs-dev-r...@openjdk.org> on behalf of Zelva Lia
<jolyj...@gmail.com>
Sent: Friday, August 19, 2022 5:49 AM
To: core-libs-dev@openjdk.org
Subject: CopyOnWriteArrayList Collection.shuffle
Hello, when shuffling the CopyOnWrite list with the standard
Collections.shuffle method, performance anomalies occur, due to the fact that
it calls the set method, which copies the array each time, a possible solution
(crutch) is a random comparator for sorting, so sorting in COW is redefined to
its own sub - blocking implementation
Another problem with Collections.shuffle is that it's not exactly thread safe
because it calls the size() method; and then iterates from it, also COW does
not support modification inside the iterator (works on snapshots)
COWCollectionsShuffle 0,008 ops/ms
COWListRandomSort 1,089 ops/ms
syncListCollectionsShuffle 0,950 ops/ms
