From 5784d7c07870ab43bd09f1d8c4141c730528a652 Mon Sep 17 00:00:00 2001
From: JarrodCTaylor <jarrod@fastmail.com>
Date: Mon, 2 Feb 2026 10:08:19 -0600
Subject: [PATCH] Fix lock contention in handler cache (Issue #38)

Replace synchronized Cache with ConcurrentHashMap
---
 .../com/cognitect/transit/impl/Cache.java     | 19 -------------------
 .../cognitect/transit/impl/ReaderFactory.java | 15 ++++++---------
 .../cognitect/transit/impl/WriterFactory.java | 17 +++++++----------
 3 files changed, 13 insertions(+), 38 deletions(-)
 delete mode 100644 src/main/java/com/cognitect/transit/impl/Cache.java

diff --git a/src/main/java/com/cognitect/transit/impl/Cache.java b/src/main/java/com/cognitect/transit/impl/Cache.java
deleted file mode 100644
index e9736f7..0000000
--- a/src/main/java/com/cognitect/transit/impl/Cache.java
+++ /dev/null
@@ -1,19 +0,0 @@
-// Copyright (c) Cognitect, Inc.
-// All rights reserved.
-
-package com.cognitect.transit.impl;
-
-import java.util.LinkedHashMap;
-import java.util.Map;
-
-public class Cache<K, V> extends LinkedHashMap<K, V> {
-
-    public Cache() {
-        super(10);
-    }
-
-    @Override
-    protected boolean removeEldestEntry(Map.Entry eldest) {
-        return size() > 10;
-    }
-}
diff --git a/src/main/java/com/cognitect/transit/impl/ReaderFactory.java b/src/main/java/com/cognitect/transit/impl/ReaderFactory.java
index 3d8f828..f3bca35 100644
--- a/src/main/java/com/cognitect/transit/impl/ReaderFactory.java
+++ b/src/main/java/com/cognitect/transit/impl/ReaderFactory.java
@@ -12,10 +12,11 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 public class ReaderFactory {
 
-    private static Map<Map<String, ReadHandler<?,?>>, ReadHandlerMap> handlerCache = new Cache<Map<String, ReadHandler<?,?>>, ReadHandlerMap>();
+    private static final ConcurrentHashMap<Map<String, ReadHandler<?,?>>, ReadHandlerMap> handlerCache = new ConcurrentHashMap<>();
 
     public static Map<String, ReadHandler<?,?>> defaultHandlers() {
 
@@ -59,14 +60,10 @@ private static Map<String, ReadHandler<?,?>> handlerMap(Map<String, ReadHandler<
             return customHandlers;
         }
 
-        synchronized (ReaderFactory.class) {
-            ReadHandlerMap readHandlerMap = handlerCache.get(customHandlers);
-            if (readHandlerMap == null) {
-                readHandlerMap = new ReadHandlerMap(customHandlers);
-                handlerCache.put(customHandlers, readHandlerMap);
-            }
-            return readHandlerMap;
-        }
+        if (customHandlers == null)
+            return new ReadHandlerMap(null);
+
+        return handlerCache.computeIfAbsent(customHandlers, ReadHandlerMap::new);
     }
 
     private static DefaultReadHandler defaultHandler(DefaultReadHandler customDefaultHandler) {
diff --git a/src/main/java/com/cognitect/transit/impl/WriterFactory.java b/src/main/java/com/cognitect/transit/impl/WriterFactory.java
index 1384b80..fabad77 100644
--- a/src/main/java/com/cognitect/transit/impl/WriterFactory.java
+++ b/src/main/java/com/cognitect/transit/impl/WriterFactory.java
@@ -13,25 +13,22 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
 
 public class WriterFactory {
 
-    private static final Map<Map<Class, WriteHandler<?,?>>, WriteHandlerMap> handlerCache = new Cache<Map<Class, WriteHandler<?,?>>, WriteHandlerMap>();
+    private static final ConcurrentHashMap<Map<Class, WriteHandler<?,?>>, WriteHandlerMap> handlerCache = new ConcurrentHashMap<>();
 
     private static WriteHandlerMap buildWriteHandlerMap(Map<Class, WriteHandler<?, ?>> customHandlers) {
         if (customHandlers instanceof WriteHandlerMap)
             return new WriteHandlerMap(customHandlers);
 
-        WriteHandlerMap writeHandlerMap;
-        synchronized (handlerCache) {
-            writeHandlerMap = handlerCache.get(customHandlers);
-            if (writeHandlerMap == null) {
-                writeHandlerMap = new WriteHandlerMap(customHandlers);
-                handlerCache.put(customHandlers, writeHandlerMap);
-            }
-        }
-        return new WriteHandlerMap(writeHandlerMap);
+        if (customHandlers == null)
+            return new WriteHandlerMap();
+
+        WriteHandlerMap cached = handlerCache.computeIfAbsent(customHandlers, WriteHandlerMap::new);
+        return new WriteHandlerMap(cached);
     }
 
     private static WriteHandlerMap verboseHandlerMap(Map<Class, WriteHandler<?, ?>> customHandlers) {