Release AggregationContext more eagerly

No need to drag a reference to this thing around until the query result
is fully release. Track it via a future (so it's unlinked on release)
and release it as soon as we set the aggregations.
Only release on aggs release and ref-counting to zero as a backup.

Author: original-brownbear

server/src/main/java/org/elasticsearch/search/DefaultSearchContext.java

@@ -26,7 +26,6 @@
 import org.elasticsearch.common.breaker.CircuitBreaker;
 import org.elasticsearch.common.lucene.search.Queries;
 import org.elasticsearch.core.Nullable;
-import org.elasticsearch.core.Releasable;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.IndexMode;
 import org.elasticsearch.index.IndexService;
@@ -51,6 +50,7 @@
 import org.elasticsearch.index.search.NestedHelper;
 import org.elasticsearch.index.shard.IndexShard;
 import org.elasticsearch.search.aggregations.SearchContextAggregations;
+import org.elasticsearch.search.aggregations.support.AggregationContext;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.collapse.CollapseContext;
 import org.elasticsearch.search.dfs.DfsSearchResult;
@@ -861,8 +861,8 @@ public QuerySearchResult queryResult() {
         return queryResult;
     }
 
-    public void addQuerySearchResultReleasable(Releasable releasable) {
-        queryResult.addReleasable(releasable);
+    public void addAggregationContext(AggregationContext aggregationContext) {
+        queryResult.addAggregationContext(aggregationContext);
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/SearchService.java

@@ -1613,7 +1613,7 @@ private void parseSource(DefaultSearchContext context, SearchSourceBuilder sourc
                 enableRewriteAggsToFilterByFilter,
                 source.aggregations().isInSortOrderExecutionRequired()
             );
-            context.addQuerySearchResultReleasable(aggContext);
+            context.addAggregationContext(aggContext);
             try {
                 final AggregatorFactories factories = source.aggregations().build(aggContext, null);
                 context.aggregations(

server/src/main/java/org/elasticsearch/search/query/QuerySearchResult.java

@@ -13,13 +13,14 @@
 import org.apache.lucene.search.TotalHits;
 import org.elasticsearch.TransportVersion;
 import org.elasticsearch.TransportVersions;
+import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.support.SubscribableListener;
 import org.elasticsearch.common.io.stream.DelayableWriteable;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.lucene.search.TopDocsAndMaxScore;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.RefCounted;
-import org.elasticsearch.core.Releasable;
 import org.elasticsearch.core.Releasables;
 import org.elasticsearch.core.SimpleRefCounted;
 import org.elasticsearch.search.DocValueFormat;
@@ -28,6 +29,7 @@
 import org.elasticsearch.search.SearchShardTarget;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
+import org.elasticsearch.search.aggregations.support.AggregationContext;
 import org.elasticsearch.search.internal.ShardSearchContextId;
 import org.elasticsearch.search.internal.ShardSearchRequest;
 import org.elasticsearch.search.profile.SearchProfileDfsPhaseResult;
@@ -37,8 +39,6 @@
 import org.elasticsearch.transport.LeakTracker;
 
 import java.io.IOException;
-import java.util.ArrayList;
-import java.util.List;
 
 import static org.elasticsearch.common.lucene.Lucene.readTopDocs;
 import static org.elasticsearch.common.lucene.Lucene.writeTopDocs;
@@ -75,7 +75,7 @@ public final class QuerySearchResult extends SearchPhaseResult {
 
     private final RefCounted refCounted;
 
-    private final List<Releasable> toRelease;
+    private final SubscribableListener<Void> aggsContextReleased;
 
     public QuerySearchResult() {
         this(false);
@@ -99,22 +99,22 @@ public QuerySearchResult(StreamInput in, boolean delayedAggregations) throws IOE
             readFromWithId(id, in, delayedAggregations);
         }
         refCounted = null;
-        toRelease = null;
+        aggsContextReleased = null;
     }
 
     public QuerySearchResult(ShardSearchContextId contextId, SearchShardTarget shardTarget, ShardSearchRequest shardSearchRequest) {
         this.contextId = contextId;
         setSearchShardTarget(shardTarget);
         isNull = false;
         setShardSearchRequest(shardSearchRequest);
-        this.toRelease = new ArrayList<>();
         this.refCounted = LeakTracker.wrap(new SimpleRefCounted());
+        this.aggsContextReleased = new SubscribableListener<>();
     }
 
     private QuerySearchResult(boolean isNull) {
         this.isNull = isNull;
         this.refCounted = null;
-        toRelease = null;
+        aggsContextReleased = null;
     }
 
     /**
@@ -275,16 +275,24 @@ public void releaseAggs() {
             aggregations.close();
             aggregations = null;
         }
+        releaseAggsContext();
     }
 
-    public void addReleasable(Releasable releasable) {
-        toRelease.add(releasable);
+    public void addAggregationContext(AggregationContext aggsContext) {
+        aggsContextReleased.addListener(ActionListener.releasing(aggsContext));
     }
 
     public void aggregations(InternalAggregations aggregations) {
         assert this.aggregations == null : "aggregations already set to [" + this.aggregations + "]";
         this.aggregations = aggregations == null ? null : DelayableWriteable.referencing(aggregations);
         hasAggs = aggregations != null;
+        releaseAggsContext();
+    }
+
+    private void releaseAggsContext() {
+        if (aggsContextReleased != null) {
+            aggsContextReleased.onResponse(null);
+        }
     }
 
     @Nullable
@@ -547,7 +555,7 @@ public boolean tryIncRef() {
     public boolean decRef() {
         if (refCounted != null) {
             if (refCounted.decRef()) {
-                Releasables.close(toRelease);
+                aggsContextReleased.onResponse(null);
                 return true;
             }
             return false;