From 0db73761b98b664334602a595464dbe93e077b73 Mon Sep 17 00:00:00 2001
From: John Montgomery <johnm@brandwatch.com>
Date: Mon, 21 Nov 2022 17:00:39 +0000
Subject: [PATCH] Cache IndexSchema on SchemaSimilarityFactory to avoid NPE
 with shared schemas

Using <bool name="shareSchema">true</bool> means that a single
SchemaSimilarityFactory would be shared between multiple cores.
Therefore inform(SolrCore) would be called multiple times.  This leads
to a race condition when the Similarity object is being used for query
at the same time as a new core is being loaded.  This results in a
NullPointerException as the new SolrCore is not yet fully initialised.
---
 .../similarities/SchemaSimilarityFactory.java    | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/solr/core/src/java/org/apache/solr/search/similarities/SchemaSimilarityFactory.java b/solr/core/src/java/org/apache/solr/search/similarities/SchemaSimilarityFactory.java
index e682b9ee5bd8..71d1d29dc174 100644
--- a/solr/core/src/java/org/apache/solr/search/similarities/SchemaSimilarityFactory.java
+++ b/solr/core/src/java/org/apache/solr/search/similarities/SchemaSimilarityFactory.java
@@ -26,6 +26,7 @@
 import org.apache.solr.common.params.SolrParams;
 import org.apache.solr.core.SolrCore;
 import org.apache.solr.schema.FieldType;
+import org.apache.solr.schema.IndexSchema;
 import org.apache.solr.schema.SimilarityFactory;
 import org.apache.solr.util.plugin.SolrCoreAware;
 
@@ -137,14 +138,16 @@ public Similarity getSimilarity() {
   
   private class SchemaSimilarity extends PerFieldSimilarityWrapper {
     private Similarity defaultSimilarity;
+    private volatile IndexSchema schema;
 
     public SchemaSimilarity(Similarity defaultSimilarity) {
       this.defaultSimilarity = defaultSimilarity;
+      schema = core.getLatestSchema();
     }
 
     @Override
     public Similarity get(String name) {
-      FieldType fieldType = core.getLatestSchema().getFieldTypeNoEx(name);
+      FieldType fieldType = getSchema().getFieldTypeNoEx(name);
       if (fieldType == null) {
         return defaultSimilarity;
       } else {
@@ -153,6 +156,17 @@ public Similarity get(String name) {
       }
     }
 
+    private IndexSchema getSchema() {
+      // if we're using shareSchema in our config we might actually have an uninitialised
+      // SolrCore, so we cache the old schema to bridge the gap, but otherwise
+      // defer to the core itself (in case the schema changes)
+      IndexSchema latestSchema = core.getLatestSchema();
+      if (latestSchema != null && schema != latestSchema) {
+        schema = latestSchema;
+      }
+      return schema;
+    }
+
     @Override
     public String toString() {
       return "SchemaSimilarity. Default: " + ((get("") == null) ? "null" : get("").toString());