Make ReactiveDefaultBookmarkManager return a copy of bookmarks

[injectives]

This update makes sure that the ReactiveDefaultBookmarkManager returns an unmodifiable copy of its current bookmarks instead of returning a view of the bookmarks.

[injectives]

fixes neo4j/neo4j-java-driver#1464

[michael-simons]

OOps.

Thank you.

[seabamirum]

At some point the code that @injectives suggested for getBookmarks()

Collections.synchronizedSet(Collections.unmodifiableSet(new HashSet<>(this.bookmarks)));

got replaced with

Set.copyOf(this.bookmarks);

which although looks a lot prettier it still doesn't prevent ConcurrentModificationException, as can be seen in the below stack trace. However, I think we only need synchronization while making the copy. I would suggest using

synchronized(this.bookmarks) { return Set.copyOf(this.bookmarks); } 

Stack trace:

java.util.ConcurrentModificationException: null	at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1605) ~[na:na] Original Stack Trace:	at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1605) ~[na:na]	at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1628) ~[na:na]	at java.base/java.util.AbstractCollection.addAll(AbstractCollection.java:337) ~[na:na]	at java.base/java.util.HashSet.<init>(HashSet.java:121) ~[na:na]	at java.base/java.util.Set.copyOf(Set.java:732) ~[na:na]	at org.springframework.data.neo4j.core.transaction.ReactiveDefaultBookmarkManager.getBookmarks(ReactiveDefaultBookmarkManager.java:53) ~[spring-data-neo4j-7.1.3.jar:7.1.3] 

[michael-simons]

That's indeed true. Excellent catch.