From 4dd4e7979d96c16f6bf023a27ae6a5a1d2f21509 Mon Sep 17 00:00:00 2001
From: Gregorius Soedharmo <arkatufus@yahoo.com>
Date: Sat, 29 Jul 2023 03:53:26 +0700
Subject: [PATCH] Fix PersistenceQuery ReadJournalFor thread safety issue

---
 .../Akka.Persistence.Query/PersistenceQuery.cs    | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/core/Akka.Persistence.Query/PersistenceQuery.cs b/src/core/Akka.Persistence.Query/PersistenceQuery.cs
index d8fe409a692..a4914001226 100644
--- a/src/core/Akka.Persistence.Query/PersistenceQuery.cs
+++ b/src/core/Akka.Persistence.Query/PersistenceQuery.cs
@@ -19,6 +19,7 @@ public sealed class PersistenceQuery : IExtension
         private readonly ExtendedActorSystem _system;
         private readonly ConcurrentDictionary<string, IReadJournal> _readJournalPluginExtensionIds = new();
         private ILoggingAdapter _log;
+        private readonly object _lock = new ();
 
         public static PersistenceQuery Get(ActorSystem system)
         {
@@ -34,8 +35,18 @@ public PersistenceQuery(ExtendedActorSystem system)
 
         public TJournal ReadJournalFor<TJournal>(string readJournalPluginId) where TJournal : IReadJournal
         {
-            var plugin = _readJournalPluginExtensionIds.GetOrAdd(readJournalPluginId, path => CreatePlugin(path, GetDefaultConfig<TJournal>()).GetReadJournal());
-            return (TJournal)plugin;
+            if(_readJournalPluginExtensionIds.TryGetValue(readJournalPluginId, out var plugin))
+                return (TJournal)plugin;
+            
+            lock (_lock)
+            {
+                if (_readJournalPluginExtensionIds.TryGetValue(readJournalPluginId, out plugin))
+                    return (TJournal)plugin;
+                
+                plugin = CreatePlugin(readJournalPluginId, GetDefaultConfig<TJournal>()).GetReadJournal();
+                _readJournalPluginExtensionIds[readJournalPluginId] = plugin;
+                return (TJournal)plugin;
+            }
         }
 
         private IReadJournalProvider CreatePlugin(string configPath, Config config)