[GitHub] [lucene-solr] shalinmangar commented on a change in pull request #1470: SOLR-14354: Async or using threads in better way for HttpShardHandler

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shalinmangar commented on a change in pull request #1470:
URL: https://github.com/apache/lucene-solr/pull/1470#discussion_r445295319



##########
File path: solr/solrj/src/java/org/apache/solr/client/solrj/util/OnComplete.java
##########
@@ -0,0 +1,33 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.solr.client.solrj.util;
+
+/**
+ * Listener for async requests
+ */
+public interface OnComplete<T> {

Review comment:
       Perhaps rename to `RequestLifecycleListener`?

##########
File path: solr/core/src/java/org/apache/solr/handler/component/HttpShardHandler.java
##########
@@ -66,16 +66,20 @@
   public static String ONLY_NRT_REPLICAS = "distribOnlyRealtime";
 
   private HttpShardHandlerFactory httpShardHandlerFactory;
-  private CompletionService<ShardResponse> completionService;
-  private Set<Future<ShardResponse>> pending;
+  private Map<ShardResponse, Cancellable> responseCancellableMap;
+  private BlockingQueue<ShardResponse> responses;
+  private AtomicInteger pending;
   private Map<String, List<String>> shardToURLs;
   private Http2SolrClient httpClient;

Review comment:
       It seems that this `Http2SolrClient` instance can be removed. It is being used in the request method but that method is not used anywhere anymore.

##########
File path: solr/core/src/java/org/apache/solr/handler/component/HttpShardHandler.java
##########
@@ -130,77 +134,64 @@ public void submit(final ShardRequest sreq, final String shard, final Modifiable
     final Tracer tracer = GlobalTracer.getTracer();
     final Span span = tracer != null ? tracer.activeSpan() : null;
 
-    Callable<ShardResponse> task = () -> {
+    params.remove(CommonParams.WT); // use default (currently javabin)
+    params.remove(CommonParams.VERSION);
+    QueryRequest req = makeQueryRequest(sreq, params, shard);
+    req.setMethod(SolrRequest.METHOD.POST);
 
-      ShardResponse srsp = new ShardResponse();
-      if (sreq.nodeName != null) {
-        srsp.setNodeName(sreq.nodeName);
-      }
-      srsp.setShardRequest(sreq);
-      srsp.setShard(shard);
-      SimpleSolrResponse ssr = new SimpleSolrResponse();
-      srsp.setSolrResponse(ssr);
-      long startTime = System.nanoTime();
+    LBSolrClient.Req lbReq = httpShardHandlerFactory.newLBHttpSolrClientReq(req, urls);
+
+    ShardResponse srsp = new ShardResponse();
+    if (sreq.nodeName != null) {
+      srsp.setNodeName(sreq.nodeName);
+    }
+    srsp.setShardRequest(sreq);
+    srsp.setShard(shard);
+    SimpleSolrResponse ssr = new SimpleSolrResponse();
+    srsp.setSolrResponse(ssr);
+
+    pending.incrementAndGet();
+    // if there are no shards available for a slice, urls.size()==0
+    if (urls.size() == 0) {
+      // TODO: what's the right error code here? We should use the same thing when
+      // all of the servers for a shard are down.
+      SolrException exception = new SolrException(SolrException.ErrorCode.SERVICE_UNAVAILABLE, "no servers hosting shard: " + shard);
+      srsp.setException(exception);
+      srsp.setResponseCode(exception.code());
+      responses.add(srsp);
+      return;
+    }
 
-      try {
-        params.remove(CommonParams.WT); // use default (currently javabin)
-        params.remove(CommonParams.VERSION);
+    // all variables that set inside this listener must be at least volatile
+    responseCancellableMap.put(srsp, this.lbClient.asyncReq(lbReq, new OnComplete<>() {
+      long startTime = System.nanoTime();

Review comment:
       This needs to be volatile or AtomicLong because it is accessed from other threads that call onSuccess and onFailure




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