From a6c058a26094bf169320d09e9fa1eff7faa5f432 Mon Sep 17 00:00:00 2001
From: Chris Hostetter <hossman@apache.org>
Date: Mon, 3 Aug 2020 09:58:16 -0700
Subject: [PATCH] SOLR-14657: Improve error handling in IndexReader realted
 metrics that were causing scary ERROR logging if metrics were requested while
 Solr was in the process of closing/re-opening a new IndexReader

---
 solr/CHANGES.txt                              |  3 ++
 .../apache/solr/search/SolrIndexSearcher.java | 29 +++++++++++++++----
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index b46ccfea886..1fc5a5f7200 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -156,6 +156,9 @@ Bug Fixes
 * SOLR-14516: Fix NPE in JSON response writer(wt=json) with /get when writing non-stored, non-indexed docvalue field
   from an uncommitted document (noble, Ishan Chattopadhyaya, Munendra S N)
 
+* SOLR-14657: Improve error handling in IndexReader realted metrics that were causing scary ERROR logging
+  if metrics were requested while Solr was in the process of closing/re-opening a new IndexReader. (hossman)
+
 Other Changes
 ---------------------
 
diff --git a/solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java b/solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java
index 4cc97586118..3ebd43c845e 100644
--- a/solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java
+++ b/solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java
@@ -35,7 +35,9 @@ import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
 
+import com.codahale.metrics.Gauge;
 import com.google.common.collect.Iterables;
+
 import org.apache.lucene.document.Document;
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.index.ExitableDirectoryReader;
@@ -51,6 +53,7 @@ import org.apache.lucene.index.Terms;
 import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.search.*;
 import org.apache.lucene.search.TotalHits.Relation;
+import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
@@ -2274,12 +2277,12 @@ public class SolrIndexSearcher extends IndexSearcher implements Closeable, SolrI
     parentContext.gauge(() -> warmupTime, true, "warmupTime", Category.SEARCHER.toString(), scope);
     parentContext.gauge(() -> registerTime, true, "registeredAt", Category.SEARCHER.toString(), scope);
     // reader stats
-    parentContext.gauge(() -> reader.numDocs(), true, "numDocs", Category.SEARCHER.toString(), scope);
-    parentContext.gauge(() -> reader.maxDoc(), true, "maxDoc", Category.SEARCHER.toString(), scope);
-    parentContext.gauge(() -> reader.maxDoc() - reader.numDocs(), true, "deletedDocs", Category.SEARCHER.toString(), scope);
-    parentContext.gauge(() -> reader.toString(), true, "reader", Category.SEARCHER.toString(), scope);
-    parentContext.gauge(() -> reader.directory().toString(), true, "readerDir", Category.SEARCHER.toString(), scope);
-    parentContext.gauge(() -> reader.getVersion(), true, "indexVersion", Category.SEARCHER.toString(), scope);
+    parentContext.gauge(rgauge(-1, () -> reader.numDocs()), true, "numDocs", Category.SEARCHER.toString(), scope);
+    parentContext.gauge(rgauge(-1, () -> reader.maxDoc()), true, "maxDoc", Category.SEARCHER.toString(), scope);
+    parentContext.gauge(rgauge(-1, () -> reader.maxDoc() - reader.numDocs()), true, "deletedDocs", Category.SEARCHER.toString(), scope);
+    parentContext.gauge(rgauge(-1, () -> reader.toString()), true, "reader", Category.SEARCHER.toString(), scope);
+    parentContext.gauge(rgauge("", () -> reader.directory().toString()), true, "readerDir", Category.SEARCHER.toString(), scope);
+    parentContext.gauge(rgauge(-1, () -> reader.getVersion()), true, "indexVersion", Category.SEARCHER.toString(), scope);
     // size of the currently opened commit
     parentContext.gauge(() -> {
       try {
@@ -2301,6 +2304,20 @@ public class SolrIndexSearcher extends IndexSearcher implements Closeable, SolrI
         }), true, "statsCache", Category.CACHE.toString(), scope);
   }
 
+  /** 
+   * wraps a gauge (related to an IndexReader) and swallows any {@link AlreadyClosedException} that 
+   * might be thrown, returning the specified default in it's place. 
+   */
+  private <T> Gauge<T> rgauge(T closedDefault, Gauge<T> g) {
+    return () -> {
+      try {
+        return g.getValue();
+      } catch (AlreadyClosedException ignore) {
+        return closedDefault;
+      }
+    };
+  }
+  
   private static class FilterImpl extends Filter {
     private final Filter topFilter;
     private final List<Weight> weights;