jpountz commented on code in PR #12374:
URL: https://github.com/apache/lucene/pull/12374#discussion_r1236671035
##########
lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java:
##########
@@ -116,8 +117,11 @@ public class IndexSearcher {
protected final IndexReaderContext readerContext;
protected final List<LeafReaderContext> leafContexts;
- /** used with executor - each slice holds a set of leafs executed within one
thread */
- private final LeafSlice[] leafSlices;
+ /**
+ * used with executor - LeafSlice supplier where each slice holds a set of
leafs executed within
+ * one thread
+ */
+ private final CachingLeafSlicesSupplier leafSlicesSupplier;
Review Comment:
Can you add a comment that we're caching it instead of creating it eagerly
to avoid calling a protected method from a constructor, which is a bad practice?
##########
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[]> {
Review Comment:
Maybe also add a comment that this class is implementing the (subtle)
double-checked locking idiom and link to something like
https://shipilev.net/blog/2014/safe-public-construction/ that describes the
traps of it?
##########
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:
It would make more sense to have to have the `executor == null` check in
`IndexSearcher#getSlices` than here so that this class focuses solely on
caching logic?
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