From 179e8d8801a84d317372c3d952e4787f704a57bd Mon Sep 17 00:00:00 2001
From: Craig Perkins <cwperx@amazon.com>
Date: Wed, 3 Jul 2024 17:06:09 -0400
Subject: [PATCH] Remove singleton limitation

Signed-off-by: Craig Perkins <cwperx@amazon.com>
---
 .../indices/SystemIndexRegistry.java          | 26 ++++++-------------
 .../org/opensearch/indices/SystemIndices.java |  3 +--
 .../indices/SystemIndicesTests.java           |  6 -----
 3 files changed, 9 insertions(+), 26 deletions(-)

diff --git a/server/src/main/java/org/opensearch/indices/SystemIndexRegistry.java b/server/src/main/java/org/opensearch/indices/SystemIndexRegistry.java
index a784adb6e82b5..27973839c6167 100644
--- a/server/src/main/java/org/opensearch/indices/SystemIndexRegistry.java
+++ b/server/src/main/java/org/opensearch/indices/SystemIndexRegistry.java
@@ -16,6 +16,7 @@
 
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.List;
@@ -27,17 +28,17 @@
 import static java.util.Collections.unmodifiableMap;
 import static org.opensearch.tasks.TaskResultsService.TASK_INDEX;
 
-class SystemIndexRegistry {
-    private static SystemIndexRegistry INSTANCE = null;
+public class SystemIndexRegistry {
     private static final SystemIndexDescriptor TASK_INDEX_DESCRIPTOR = new SystemIndexDescriptor(TASK_INDEX + "*", "Task Result Index");
-    static final Map<String, Collection<SystemIndexDescriptor>> SERVER_SYSTEM_INDEX_DESCRIPTORS = singletonMap(
+    private static final Map<String, Collection<SystemIndexDescriptor>> SERVER_SYSTEM_INDEX_DESCRIPTORS = singletonMap(
         TaskResultsService.class.getName(),
         singletonList(TASK_INDEX_DESCRIPTOR)
     );
-    private static String[] SYSTEM_INDEX_PATTERNS = new String[0];
-    static Collection<SystemIndexDescriptor> SYSTEM_INDEX_DESCRIPTORS;
 
-    private SystemIndexRegistry(Map<String, Collection<SystemIndexDescriptor>> pluginAndModulesDescriptors) {
+    private volatile static String[] SYSTEM_INDEX_PATTERNS = new String[0];
+    volatile static Collection<SystemIndexDescriptor> SYSTEM_INDEX_DESCRIPTORS = Collections.emptyList();
+
+    static void register(Map<String, Collection<SystemIndexDescriptor>> pluginAndModulesDescriptors) {
         final Map<String, Collection<SystemIndexDescriptor>> descriptorsMap = buildSystemIndexDescriptorMap(pluginAndModulesDescriptors);
         checkForOverlappingPatterns(descriptorsMap);
         List<SystemIndexDescriptor> descriptors = pluginAndModulesDescriptors.values()
@@ -45,17 +46,11 @@ private SystemIndexRegistry(Map<String, Collection<SystemIndexDescriptor>> plugi
             .flatMap(Collection::stream)
             .collect(Collectors.toList());
         descriptors.add(TASK_INDEX_DESCRIPTOR);
+
         SYSTEM_INDEX_DESCRIPTORS = descriptors.stream().collect(Collectors.toUnmodifiableList());
         SYSTEM_INDEX_PATTERNS = descriptors.stream().map(SystemIndexDescriptor::getIndexPattern).toArray(String[]::new);
     }
 
-    public static synchronized SystemIndexRegistry initialize(Map<String, Collection<SystemIndexDescriptor>> pluginAndModulesDescriptors) {
-        if (INSTANCE == null) {
-            INSTANCE = new SystemIndexRegistry(pluginAndModulesDescriptors);
-        }
-        return INSTANCE;
-    }
-
     public static List<String> matchesSystemIndexPattern(String... indexExpressions) {
         return Arrays.stream(indexExpressions)
             .filter(pattern -> Regex.simpleMatch(SYSTEM_INDEX_PATTERNS, pattern))
@@ -123,9 +118,4 @@ private static Map<String, Collection<SystemIndexDescriptor>> buildSystemIndexDe
         });
         return unmodifiableMap(map);
     }
-
-    // visible for testing
-    static void clear() {
-        INSTANCE = null;
-    }
 }
diff --git a/server/src/main/java/org/opensearch/indices/SystemIndices.java b/server/src/main/java/org/opensearch/indices/SystemIndices.java
index 28e3f50b444a3..bbf58fe91512f 100644
--- a/server/src/main/java/org/opensearch/indices/SystemIndices.java
+++ b/server/src/main/java/org/opensearch/indices/SystemIndices.java
@@ -62,8 +62,7 @@ public class SystemIndices {
     private final CharacterRunAutomaton runAutomaton;
 
     public SystemIndices(Map<String, Collection<SystemIndexDescriptor>> pluginAndModulesDescriptors) {
-        SystemIndexRegistry.initialize(pluginAndModulesDescriptors);
-        SystemIndexRegistry.initialize(pluginAndModulesDescriptors);
+        SystemIndexRegistry.register(pluginAndModulesDescriptors);
         this.runAutomaton = buildCharacterRunAutomaton(SystemIndexRegistry.SYSTEM_INDEX_DESCRIPTORS);
     }
 
diff --git a/server/src/test/java/org/opensearch/indices/SystemIndicesTests.java b/server/src/test/java/org/opensearch/indices/SystemIndicesTests.java
index 12836ae7892ea..8ac457c32d53a 100644
--- a/server/src/test/java/org/opensearch/indices/SystemIndicesTests.java
+++ b/server/src/test/java/org/opensearch/indices/SystemIndicesTests.java
@@ -37,7 +37,6 @@
 import org.opensearch.plugins.SystemIndexPlugin;
 import org.opensearch.tasks.TaskResultsService;
 import org.opensearch.test.OpenSearchTestCase;
-import org.junit.Before;
 
 import java.util.Arrays;
 import java.util.Collection;
@@ -56,11 +55,6 @@
 
 public class SystemIndicesTests extends OpenSearchTestCase {
 
-    @Before
-    public void setup() {
-        SystemIndexRegistry.clear();
-    }
-
     public void testBasicOverlappingPatterns() {
         SystemIndexDescriptor broadPattern = new SystemIndexDescriptor(".a*c*", "test");
         SystemIndexDescriptor notOverlapping = new SystemIndexDescriptor(".bbbddd*", "test");