sohami commented on code in PR #12374:
URL: https://github.com/apache/lucene/pull/12374#discussion_r1237934932
##########
lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java:
##########
@@ -1014,4 +1021,48 @@ private static SliceExecutor
getSliceExecutionControlPlane(Executor executor) {
return new SliceExecutor(executor);
}
+
+ /**
+ * Supplier for {@link LeafSlice} slices when passed in executor is
non-null. This supplier
+ * computes and caches the value on first invocation and returns cached
value on subsequent
+ * invocation. If the passed in provider for slice computation throws
exception then same will be
+ * passed to the caller of this supplier on each invocation. If the provider
returns null then
+ * {@link NullPointerException} will be thrown to the caller.
+ */
+ private static class CachingLeafSlicesSupplier implements
Supplier<LeafSlice[]> {
+ private volatile LeafSlice[] leafSlices;
+
+ private final Executor executor;
+
+ private final Function<List<LeafReaderContext>, LeafSlice[]> sliceProvider;
+
+ private final List<LeafReaderContext> leaves;
+
+ private CachingLeafSlicesSupplier(
+ Executor executor,
+ Function<List<LeafReaderContext>, LeafSlice[]> provider,
+ List<LeafReaderContext> leaves) {
+ this.executor = executor;
+ this.sliceProvider = Objects.requireNonNull(provider, "leaf slice
provider cannot be null");
+ this.leaves = Objects.requireNonNull(leaves, "list of LeafReaderContext
cannot be null");
+ }
+
+ @Override
+ public LeafSlice[] get() {
+ if (executor == null) {
+ return null;
+ }
Review Comment:
I did it this way because `IndexSearcher` can access `leafSlicesSupplier`
without using `getSlices`. So everywhere it will need to perform explicit check
for executor being `non-null` too for such usages. With current mechanism non
null check for executor will not be needed for any future usages as well. This
is also keeping the current behavior to return `null` slices when `executor` is
`null`
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