madrob commented on a change in pull request #1358: SOLR-14256: replaced EMPTY
with empty() to fix deadlock
URL: https://github.com/apache/lucene-solr/pull/1358#discussion_r394057677
##########
File path: solr/core/src/java/org/apache/solr/search/DocSet.java
##########
@@ -36,6 +36,21 @@
assert this instanceof BitDocSet || this instanceof SortedIntDocSet;
}
+ // we can't simply use a trivial static initializer "= new SortedIntDocSet"
because it can lead to classloader deadlock
+ private static DocSet EMPTY;
+
+ /** An empty instance. */
+ public static DocSet empty() {
Review comment:
If you do the singleton holder idiom then you don't need to have a null
check (at the cost of an extra class, but the VM takes care of this quickly)
[Effective Java 3rd Ed, Item 83]
```
private static class LazyHolder {
static final DocSet INSTANCE = new SortedIntDocSet(new int[0]);
}
public static DocSet empty() {
return LazyHolder.INSTANCE;
}
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