virajjasani commented on a change in pull request #3148:
URL: https://github.com/apache/hadoop/pull/3148#discussion_r659601136



##########
File path: 
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java
##########
@@ -2272,19 +2274,11 @@ public int getActiveTransferThreadCount() {
   void incrDatanodeNetworkErrors(String host) {
     metrics.incrDatanodeNetworkErrors();
 
-    /*
-     * Synchronizing on the whole cache is a big hammer, but since it's only
-     * accumulating errors, it should be ok. If this is ever expanded to 
include
-     * non-error stats, then finer-grained concurrency should be applied.
-     */
-    synchronized (datanodeNetworkCounts) {
-      try {
-        final Map<String, Long> curCount = datanodeNetworkCounts.get(host);
-        curCount.put("networkErrors", curCount.get("networkErrors") + 1L);
-        datanodeNetworkCounts.put(host, curCount);
-      } catch (ExecutionException e) {
-        LOG.warn("failed to increment network error counts for host: {}", 
host);
-      }
+    try {
+      datanodeNetworkCounts.get(host).compute(NETWORK_ERRORS,
+          (key, errors) -> errors == null ? null : errors + 1L);

Review comment:
       > i mean, shouldn't it be made 1 when errors is null (meaning the key 
didn't exist before)?
   
   I see. Based on the LoadingCache creation, we will always find value `0L` at 
the beginning and the only reason why I handled `errors == null` case is 
because findbugs don't complain about missing this. But I think your suggestion 
is better, we should return error `1L` when it is null. Let me change this.




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