Use ReentrantLock instead of synchronized to avoid deadlock on pinning

Author: oddbjornkvalsund

src/main/java/com/fasterxml/jackson/databind/deser/DeserializerCache.java

@@ -1,6 +1,7 @@
 package com.fasterxml.jackson.databind.deser;
 
 import java.util.HashMap;
+import java.util.concurrent.locks.ReentrantLock;
 
 import com.fasterxml.jackson.annotation.JsonFormat;
 import com.fasterxml.jackson.databind.*;
@@ -52,6 +53,12 @@ public final class DeserializerCache
     protected final HashMap<JavaType, JsonDeserializer<Object>> _incompleteDeserializers
         = new HashMap<JavaType, JsonDeserializer<Object>>(8);
 
+
+    /**
+     * We hold an explicit lock while creating deserializers to avoid creating duplicates.
+     */
+    private final ReentrantLock _incompleteDeserializersLock = new ReentrantLock();
+
     /*
     /**********************************************************
     /* Life-cycle
@@ -246,7 +253,9 @@ protected JsonDeserializer<Object> _createAndCacheValueDeserializer(Deserializat
          * limitations necessary to ensure that only completely initialized ones
          * are visible and used.
          */
-        synchronized (_incompleteDeserializers) {
+        try {
+            _incompleteDeserializersLock.lock();
+
             // Ok, then: could it be that due to a race condition, deserializer can now be found?
             JsonDeserializer<Object> deser = _findCachedDeserializer(type);
             if (deser != null) {
@@ -269,6 +278,8 @@ protected JsonDeserializer<Object> _createAndCacheValueDeserializer(Deserializat
                     _incompleteDeserializers.clear();
                 }
             }
+        } finally {
+            _incompleteDeserializersLock.unlock();
         }
     }