From 1568ada5215b1b2e9ee7ffca28fcd6cbcef73944 Mon Sep 17 00:00:00 2001
From: MKaramavrov <makcumkaka@gmail.com>
Date: Tue, 14 May 2024 16:31:14 +0300
Subject: [PATCH] dev.morphia.Datastore Thread Safety #2802  - fix for Mapper
 thread safety issue when mapped using the same discriminator value

---
 .../main/java/dev/morphia/mapping/Mapper.java | 36 +++++++++++--------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/core/src/main/java/dev/morphia/mapping/Mapper.java b/core/src/main/java/dev/morphia/mapping/Mapper.java
index 0d1a6e32cdb..0661611a9f9 100644
--- a/core/src/main/java/dev/morphia/mapping/Mapper.java
+++ b/core/src/main/java/dev/morphia/mapping/Mapper.java
@@ -77,6 +77,7 @@ public class Mapper {
     private final List<EntityListener<?>> listeners = new ArrayList<>();
     private final MorphiaConfig config;
     private final DiscriminatorLookup discriminatorLookup;
+    private final Object entityRegistrationMonitor = new Object();
 
     /**
      * Creates a Mapper with the given options.
@@ -567,22 +568,27 @@ private EntityModel register(EntityModel model, boolean validate) {
         var existing = mappedEntities.get(model.getType().getName());
         if (existing != null) {
             return existing;
+        } else {
+            synchronized (entityRegistrationMonitor) {
+                existing = mappedEntities.get(model.getType().getName());
+                if (existing != null) {
+                    return existing;
+                } else {
+                    mappedEntities.put(model.getType().getName(), model);
+                    if (validate && !model.isInterface()) {
+                        new MappingValidator().validate(this, model);
+                    }
+                    discriminatorLookup.addModel(model);
+                    mappedEntitiesByCollection.computeIfAbsent(model.getCollectionName(), s -> new CopyOnWriteArraySet<>()).add(model);
+
+                    EntityModel superClass = model.getSuperClass();
+                    if (superClass != null) {
+                        superClass.addSubtype(model);
+                    }
+                    return model;
+                }
+            }
         }
-        mappedEntities.put(model.getType().getName(), model);
-
-        if (validate && !model.isInterface()) {
-            new MappingValidator()
-                    .validate(this, model);
-        }
-        discriminatorLookup.addModel(model);
-        mappedEntitiesByCollection.computeIfAbsent(model.getCollectionName(), s -> new CopyOnWriteArraySet<>())
-                .add(model);
-        EntityModel superClass = model.getSuperClass();
-        if (superClass != null) {
-            superClass.addSubtype(model);
-        }
-
-        return model;
     }
 
     private List<Class> getClasses(String packageName)