[GitHub] [iceberg] amogh-jahagirdar commented on a diff in pull request #6857: Core,AWS: Init ObjectMapper with AtomicReference

["amogh-jahagirdar (via GitHub)" <gi...@apache.org>]

amogh-jahagirdar commented on code in PR #6857:
URL: https://github.com/apache/iceberg/pull/6857#discussion_r1111060602


##########
aws/src/main/java/org/apache/iceberg/aws/s3/signer/S3ObjectMapper.java:
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@@ -42,26 +43,24 @@
 
 public class S3ObjectMapper {
 
-  private static final JsonFactory FACTORY = new JsonFactory();
-  private static final ObjectMapper MAPPER = new ObjectMapper(FACTORY);
-  private static volatile boolean isInitialized = false;
+  private static final AtomicReference<ObjectMapper> REFERENCE = new AtomicReference<>();
 
   private S3ObjectMapper() {}
 
   static ObjectMapper mapper() {
-    if (!isInitialized) {
-      synchronized (S3ObjectMapper.class) {
-        if (!isInitialized) {
-          MAPPER.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
-          MAPPER.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
-          MAPPER.setPropertyNamingStrategy(PropertyNamingStrategies.KebabCaseStrategy.INSTANCE);
-          MAPPER.registerModule(initModule());
-          isInitialized = true;
-        }
-      }
+    if (null == REFERENCE.get()) {

Review Comment:
   Yeah it's a good question. It really is more of a cleanliness thing imo, it just felt a bit unnecessary to have double check locking when atomic reference already encapsulates a few of the aspects we care about. 
   
   For avoiding the unnecessary work being done by one thread in the situation you described, could we make the mapper() method itself synchronized? That way two threads cannot init at the same time anyways, and the second thread will see the atomic reference is set and not do any work.



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